# Chat with Java and Servlets

> \[!WARNING]
>
> As the Programmable Chat API is set to [sunset in 2022](https://www.twilio.com/en-us/changelog/programmable-chat-end-of-life-notice), we will no longer maintain these chat tutorials.
>
> Please see our [Conversations API QuickStart](/docs/conversations/quickstart) to start building robust virtual spaces for conversation.

> \[!CAUTION]
>
> Programmable Chat has been deprecated and is no longer supported. Instead, we'll be focusing on the next generation of chat: Twilio Conversations. Find out more about the [EOL process here](https://www.twilio.com/en-us/changelog/programmable-chat-end-of-life-notice).
>
> If you're starting a new project, please visit the [Conversations Docs](/docs/conversations) to begin. If you've already built on Programmable Chat, please visit our [Migration Guide](/docs/conversations/migrating-chat-conversations) to learn about how to switch.

Ready to implement a chat application using Twilio Programmable Chat Client?

This application allows users to exchange messages through different channels, using the Twilio Programmable Chat API. In this example, we'll show how to use this API capabilities to manage channels and their usages.

*[Properati built a web and mobile messaging app to help real estate buyers and sellers connect in real time. Learn more here.](https://customers.twilio.com/1234/properati/)*

For your convenience, we consolidated the source code for this tutorial in a single [GitHub repository](https://github.com/TwilioDevEd/twiliochat-servlets). Feel free to clone it and tweak it as required.

## Generate the Token

In order to create a Twilio Programmable Chat client, you will need an [access token](/docs/iam/access-tokens). This token holds information about your Twilio Account and Chat API keys.

We generate this token by creating a new `AccessToken` and providing it with a `ChatGrant`. With the `AccessToken` at hand, we can use its method `ToJWT()` to return its string representation.

```java title="Generate an Access Token" description="src/main/java/com/twilio/chat/TwilioTokenCreator.java"
// !mark(20,21,22,23,24,25,26,27,28,29,30,31,32)
package com.twilio.chat;

import javax.inject.Inject;

import com.twilio.jwt.accesstoken.AccessToken;
import com.twilio.jwt.accesstoken.ChatGrant;

public class TwilioTokenCreator {

  private final AppConfig appConfig;

  @Inject
  public TwilioTokenCreator(AppConfig appConfig) {
    this.appConfig = appConfig;
    if (appConfig.isIncomplete()) {
      throw new IncompleteConfigException(appConfig);
    }
  }

  String generateToken(String identity) {
    ChatGrant grant = new ChatGrant();
    grant.setServiceSid(appConfig.getTwilioChatServiceSID());

    AccessToken token = new AccessToken.Builder(
      appConfig.getTwilioAccountSID(),
      appConfig.getTwilioAPIKey(),
      appConfig.getTwilioAPISecret()
    ).identity(identity).grant(grant).build();

    return token.toJwt();
  }
}
```

We can generate a token, now we need a way for the chat app to get it.

## Token Generation Controller

On our controller we expose the endpoint responsible for providing a valid token. Using this parameter:

* `identity`: identifies the user itself.

It uses `tokenGenerator.Generate` method to get hold of a new token and return it in a JSON format to be used for our client.

```java title="Token Generation Controller" description="src/main/java/com/twilio/chat/TokenServlet.java"
// !mark(26,27,28,29,30,31,32,33,34,35,36,37,38,39,40)
package com.twilio.chat;

import java.io.BufferedWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.inject.Inject;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.Gson;
import com.google.inject.Singleton;

@Singleton
public class TokenServlet extends HttpServlet {

  private final TwilioTokenCreator tokenCreator;

  @Inject
  public TokenServlet(TwilioTokenCreator tokenCreator) {
    this.tokenCreator = tokenCreator;
  }

  @Override
  public void doPost(HttpServletRequest request, HttpServletResponse response) {
    String identity = request.getParameter("identity");

    if (identity != null) {

      String generatedToken = tokenCreator.generateToken(identity);

      Map<String, String> json = new HashMap<>();
      json.put("identity", identity);
      json.put("token", generatedToken);
      renderJson(response, json);
    }

  }

  private void renderJson(HttpServletResponse response, Map<String, String> json) {
    Gson gson = new Gson();
    response.setContentType("application/json");
    try (BufferedWriter responseWriter = new BufferedWriter(response.getWriter())) {
      responseWriter.write(gson.toJson(json));
      responseWriter.flush();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

```

Now that we have a route that generates JWT tokens on demand, let's use this route to initialize our Twilio Chat Client.

## Initialize the Programmable Chat Client

On our client, we fetch a new Token using a `POST` request to our endpoint.

With the token, we can create a new `Twilio.AccessManager`, and initialize our `Twilio.Chat.Client`.

```js title="Initialize the Chat Client" description="src/main/webapp/js/twiliochat.js"
// !mark(82,83,84,85,86,87,88,89,94,95)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

Now that we've initialized our Chat Client, let's see how we can get a list of channels.

## Get the Channel List

After initializing the client, we can call its method [`getPublicChannelDescriptors`](/docs/chat/channels) to retrieve all visible channels. The method returns a promise which we use to show the list of channels retrieved on the UI.

```js title="Get the Channel List" description="src/main/webapp/js/twiliochat.js"
// !mark(128,129,130,131,132,133,134,135,136)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

Next, we need a default channel.

## Join the General Channel

This application will try to join a channel called "General Channel" when it starts. If the channel doesn't exist, we'll create one with that name. The scope of this example application will show you how to work only with public channels, but the Programmable Chat client allows you to create private channels and handles invitations.

Notice we set a unique name for the general channel as we don't want to create a new general channel every time we start the application.

```js title="Join the General Channel" description="src/main/webapp/js/twiliochat.js"
// !mark(140,141,142,143,144,145,146,147,148,149,150,151)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

Now let's listen for some channel events.

## Listen to Channel Events

Next we listen for [channel events](/docs/chat/channels). In our case, we're setting listeners to the following events:

* `messageAdded`: When another member sends a message to the channel you are connected to.
* `typingStarted`: When another member is typing a message on the channel that you are connected to.
* `typingEnded`: When another member stops typing a message on the channel that you are connected to.
* `memberJoined`: When another member joins the channel that you are connected to.
* `memberLeft`: When another member leaves the channel that you are connected to.

We register a different function to handle each particular event.

```js title="Listen to Channel Events" description="src/main/webapp/js/twiliochat.js"
// !mark(100,101,102,99)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

The client emits events as well. Let's see how we can listen to those events as well.

## Listen to Client Events

Just like with channels, we can register handlers for [events](/docs/chat) on the Client:

* `channelAdded`: When a channel becomes visible to the Client.
* `channelRemoved`: When a channel is no longer visible to the Client.
* `tokenExpired`: When the supplied token expires.

```js title="Listen to Client Events" description="src/main/webapp/js/twiliochat.js"
// !mark(327,328,329,330,331,332,333,334,335,336,337)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

We've actually got a real chat app going here, but let's make it more interesting with multiple channels.

## Create a Channel

When a user clicks on the "+ Channel" link we'll show an input text field where it's possible to type the name of the new channel. Creating a channel involves calling `createChannel` with an object that has the `friendlyName` key. You can create a channel with more options listed on the [Channels section](/docs/chat/channels) of the Programmable Chat documentation.

```js title="Create a Channel" description="src/main/webapp/js/twiliochat.js"
// !mark(60,61,62,63,64,65,66,67,68)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

Next, we will see how we can switch between channels.

## Join Other Channels

When you tap on the name of a channel from the sidebar, that channel is set as the `selectedChannel`. The `selectChannel` method takes care of joining to the selected channel and setting up the `selectedChannel`.

```js title="Join Other Channels" description="src/main/webapp/js/twiliochat.js"
// !mark(300,301,302,303,304,305,306,307,308,309,310)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

At some point, your users will want to delete a channel. Let's have a look at how that can be done.

## Delete a Channel

The application lets the user delete the channel they are currently joining through the "delete current channel" link. The only thing you need to do to actually delete the channel from Twilio is call the [`delete`](https://media.twiliocdn.com/sdk/js/chat/releases/0.11.1/docs/Channel.html) method on the channel you are trying to delete. Like other methods on the `Channel` object, it'll return a promise where you can set the success handler.

```js title="Delete a Channel" description="src/main/webapp/js/twiliochat.js"
// !mark(313,314,315,316,317,318,319,320,321,322,323,324,325)
var twiliochat = (function() {
  var tc = {};

  var GENERAL_CHANNEL_UNIQUE_NAME = 'general';
  var GENERAL_CHANNEL_NAME = 'General Channel';
  var MESSAGES_HISTORY_LIMIT = 50;

  var $channelList;
  var $inputText;
  var $usernameInput;
  var $statusRow;
  var $connectPanel;
  var $newChannelInputRow;
  var $newChannelInput;
  var $typingRow;
  var $typingPlaceholder;

  $(document).ready(function() {
    tc.$messageList = $('#message-list');
    $channelList = $('#channel-list');
    $inputText = $('#input-text');
    $usernameInput = $('#username-input');
    $statusRow = $('#status-row');
    $connectPanel = $('#connect-panel');
    $newChannelInputRow = $('#new-channel-input-row');
    $newChannelInput = $('#new-channel-input');
    $typingRow = $('#typing-row');
    $typingPlaceholder = $('#typing-placeholder');
    $usernameInput.focus();
    $usernameInput.on('keypress', handleUsernameInputKeypress);
    $inputText.on('keypress', handleInputTextKeypress);
    $newChannelInput.on('keypress', tc.handleNewChannelInputKeypress);
    $('#connect-image').on('click', connectClientWithUsername);
    $('#add-channel-image').on('click', showAddChannelInput);
    $('#leave-span').on('click', disconnectClient);
    $('#delete-channel-span').on('click', deleteCurrentChannel);
  });

  function handleUsernameInputKeypress(event) {
    if (event.keyCode === 13){
      connectClientWithUsername();
    }
  }

  function handleInputTextKeypress(event) {
    if (event.keyCode === 13) {
      tc.currentChannel.sendMessage($(this).val());
      event.preventDefault();
      $(this).val('');
    }
    else {
      notifyTyping();
    }
  }

  var notifyTyping = $.throttle(function() {
    tc.currentChannel.typing();
  }, 1000);

  tc.handleNewChannelInputKeypress = function(event) {
    if (event.keyCode === 13) {
      tc.messagingClient.createChannel({
        friendlyName: $newChannelInput.val()
      }).then(hideAddChannelInput);
      $(this).val('');
      event.preventDefault();
    }
  };

  function connectClientWithUsername() {
    var usernameText = $usernameInput.val();
    $usernameInput.val('');
    if (usernameText == '') {
      alert('Username cannot be empty');
      return;
    }
    tc.username = usernameText;
    fetchAccessToken(tc.username, connectMessagingClient);
  }

  function fetchAccessToken(username, handler) {
    $.post('/twiliochat-servlets/token', {identity: username}, null, 'json')
      .done(function(response) {
        console.log('Successfully finished fetch of the Access Token.');
        handler(response.token);
      })
      .fail(function(error) {
        console.log('Failed to fetch the Access Token with error: ' + error);
      });
  }

  function connectMessagingClient(token) {
    // Initialize the Chat messaging client
    tc.accessManager = new Twilio.AccessManager(token);
    Twilio.Chat.Client.create(token).then(function(client) {
      tc.messagingClient = client;
      updateConnectedUI();
      tc.loadChannelList(tc.joinGeneralChannel);
      tc.messagingClient.on('channelAdded', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('channelRemoved', $.throttle(tc.loadChannelList));
      tc.messagingClient.on('tokenExpired', refreshToken);
    });
  }

  function refreshToken() {
    fetchAccessToken(tc.username, setNewToken);
  }

  function setNewToken(tokenResponse) {
    tc.accessManager.updateToken(tokenResponse.token);
  }

  function updateConnectedUI() {
    $('#username-span').text(tc.username);
    $statusRow.addClass('connected').removeClass('disconnected');
    tc.$messageList.addClass('connected').removeClass('disconnected');
    $connectPanel.addClass('connected').removeClass('disconnected');
    $inputText.addClass('with-shadow');
    $typingRow.addClass('connected').removeClass('disconnected');
  }

  tc.loadChannelList = function(handler) {
    if (tc.messagingClient === undefined) {
      console.log('Client is not initialized');
      return;
    }

    tc.messagingClient.getPublicChannelDescriptors().then(function(channels) {
      tc.channelArray = tc.sortChannelsByName(channels.items);
      $channelList.text('');
      tc.channelArray.forEach(addChannel);
      if (typeof handler === 'function') {
        handler();
      }
    });
  };

  tc.joinGeneralChannel = function() {
    console.log('Attempting to join "general" chat channel...');
    if (!tc.generalChannel) {
      // If it doesn't exist, let's create it
      tc.messagingClient.createChannel({
        uniqueName: GENERAL_CHANNEL_UNIQUE_NAME,
        friendlyName: GENERAL_CHANNEL_NAME
      }).then(function(channel) {
        console.log('Created general channel');
        tc.generalChannel = channel;
        tc.loadChannelList(tc.joinGeneralChannel);
      });
    }
    else {
      console.log('Found general channel:');
      setupChannel(tc.generalChannel);
    }
  };

  function initChannel(channel) {
    console.log('Initialized channel ' + channel.friendlyName);
    return tc.messagingClient.getChannelBySid(channel.sid);
  }

  function joinChannel(_channel) {
    return _channel.join()
      .then(function(joinedChannel) {
        console.log('Joined channel ' + joinedChannel.friendlyName);
        updateChannelUI(_channel);
        tc.currentChannel = _channel;
        tc.loadMessages();
        return joinedChannel;
      });
  }

  function initChannelEvents() {
    console.log(tc.currentChannel.friendlyName + ' ready.');
    tc.currentChannel.on('messageAdded', tc.addMessageToList);
    tc.currentChannel.on('typingStarted', showTypingStarted);
    tc.currentChannel.on('typingEnded', hideTypingStarted);
    tc.currentChannel.on('memberJoined', notifyMemberJoined);
    tc.currentChannel.on('memberLeft', notifyMemberLeft);
    $inputText.prop('disabled', false).focus();
  }

  function setupChannel(channel) {
    return leaveCurrentChannel()
      .then(function() {
        return initChannel(channel);
      })
      .then(function(_channel) {
        return joinChannel(_channel);
      })
      .then(initChannelEvents);
  }

  tc.loadMessages = function() {
    tc.currentChannel.getMessages(MESSAGES_HISTORY_LIMIT)
      .then(function(messages) {
        messages.items.forEach(tc.addMessageToList);
    });
  };

  function leaveCurrentChannel() {
    if (tc.currentChannel) {
      return tc.currentChannel.leave().then(function(leftChannel) {
        console.log('left ' + leftChannel.friendlyName);
        leftChannel.removeListener('messageAdded', tc.addMessageToList);
        leftChannel.removeListener('typingStarted', showTypingStarted);
        leftChannel.removeListener('typingEnded', hideTypingStarted);
        leftChannel.removeListener('memberJoined', notifyMemberJoined);
        leftChannel.removeListener('memberLeft', notifyMemberLeft);
      });
    } else {
      return Promise.resolve();
    }
  }

  tc.addMessageToList = function(message) {
    var rowDiv = $('<div>').addClass('row no-margin');
    rowDiv.loadTemplate($('#message-template'), {
      username: message.author,
      date: dateFormatter.getTodayDate(message.dateCreated),
      body: message.body
    });
    if (message.author === tc.username) {
      rowDiv.addClass('own-message');
    }

    tc.$messageList.append(rowDiv);
    scrollToMessageListBottom();
  };

  function notifyMemberJoined(member) {
    notify(member.identity + ' joined the channel')
  }

  function notifyMemberLeft(member) {
    notify(member.identity + ' left the channel');
  }

  function notify(message) {
    var row = $('<div>').addClass('col-md-12');
    row.loadTemplate('#member-notification-template', {
      status: message
    });
    tc.$messageList.append(row);
    scrollToMessageListBottom();
  }

  function showTypingStarted(member) {
    $typingPlaceholder.text(member.identity + ' is typing...');
  }

  function hideTypingStarted(member) {
    $typingPlaceholder.text('');
  }

  function scrollToMessageListBottom() {
    tc.$messageList.scrollTop(tc.$messageList[0].scrollHeight);
  }

  function updateChannelUI(selectedChannel) {
    var channelElements = $('.channel-element').toArray();
    var channelElement = channelElements.filter(function(element) {
      return $(element).data().sid === selectedChannel.sid;
    });
    channelElement = $(channelElement);
    if (tc.currentChannelContainer === undefined && selectedChannel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.currentChannelContainer = channelElement;
    }
    tc.currentChannelContainer.removeClass('selected-channel').addClass('unselected-channel');
    channelElement.removeClass('unselected-channel').addClass('selected-channel');
    tc.currentChannelContainer = channelElement;
  }

  function showAddChannelInput() {
    if (tc.messagingClient) {
      $newChannelInputRow.addClass('showing').removeClass('not-showing');
      $channelList.addClass('showing').removeClass('not-showing');
      $newChannelInput.focus();
    }
  }

  function hideAddChannelInput() {
    $newChannelInputRow.addClass('not-showing').removeClass('showing');
    $channelList.addClass('not-showing').removeClass('showing');
    $newChannelInput.val('');
  }

  function addChannel(channel) {
    if (channel.uniqueName === GENERAL_CHANNEL_UNIQUE_NAME) {
      tc.generalChannel = channel;
    }
    var rowDiv = $('<div>').addClass('row channel-row');
    rowDiv.loadTemplate('#channel-template', {
      channelName: channel.friendlyName
    });

    var channelP = rowDiv.children().children().first();

    rowDiv.on('click', selectChannel);
    channelP.data('sid', channel.sid);
    if (tc.currentChannel && channel.sid === tc.currentChannel.sid) {
      tc.currentChannelContainer = channelP;
      channelP.addClass('selected-channel');
    }
    else {
      channelP.addClass('unselected-channel')
    }

    $channelList.append(rowDiv);
  }

  function deleteCurrentChannel() {
    if (!tc.currentChannel) {
      return;
    }
    if (tc.currentChannel.sid === tc.generalChannel.sid) {
      alert('You cannot delete the general channel');
      return;
    }
    tc.currentChannel.delete().then(function(channel) {
      console.log('channel: '+ channel.friendlyName + ' deleted');
      setupChannel(tc.generalChannel);
    });
  }

  function selectChannel(event) {
    var target = $(event.target);
    var channelSid = target.data().sid;
    var selectedChannel = tc.channelArray.filter(function(channel) {
      return channel.sid === channelSid;
    })[0];
    if (selectedChannel === tc.currentChannel) {
      return;
    }
    setupChannel(selectedChannel);
  };

  function disconnectClient() {
    leaveCurrentChannel();
    $channelList.text('');
    tc.$messageList.text('');
    channels = undefined;
    $statusRow.addClass('disconnected').removeClass('connected');
    tc.$messageList.addClass('disconnected').removeClass('connected');
    $connectPanel.addClass('disconnected').removeClass('connected');
    $inputText.removeClass('with-shadow');
    $typingRow.addClass('disconnected').removeClass('connected');
  }

  tc.sortChannelsByName = function(channels) {
    return channels.sort(function(a, b) {
      if (a.friendlyName === GENERAL_CHANNEL_NAME) {
        return -1;
      }
      if (b.friendlyName === GENERAL_CHANNEL_NAME) {
        return 1;
      }
      return a.friendlyName.localeCompare(b.friendlyName);
    });
  };

  return tc;
})();

```

That's it! We've just implemented a chat application for Java using the Servlet API.

## Where to Next?

If you are a Java developer working with Twilio, you might want to check out these other tutorials:

**[SMS and MMS Notifications](https://www.twilio.com/blog/server-notifications-java-servlets)**

Never miss another server outage. Learn how to build a server notification system that will alert all administrators via SMS when a server outage occurs.

**[Workflow Automation](/docs/messaging/tutorials/workflow-automation/java)**

Increase your rate of response by automating the workflows that are key to your business. In this tutorial, learn how to build a ready-for-scale automated SMS workflow, for a vacation rental company.

**[Masked Phone Numbers](/docs/messaging/tutorials/masked-numbers/java)**

Protect your users' privacy by anonymously connecting them with Twilio Voice and SMS. Learn how to create disposable phone numbers on-demand, so two users can communicate without exchanging personal information.

### **Did this help?**

Thanks for checking out this tutorial! If you have any feedback to share with us, we'd love to hear it. Tweet [@twilio](http://twitter.com/twilio) to let us know what you think.