Pusher Channels client library for Java targeting Android and general Java.

• Java SE - supports versions 8, 9, 10 and 11.
• Oracle JDK
• OpenJDK
• Android, via this wrapper SDK

This README covers the following topics:

• Installation
  • Maven
  • Gradle
  • Download
  • Source
• API Overview
• The Pusher constructor
• Connecting
• Reconnecting
• Disconnecting
• Listening to connection events
• Subscribing to channels
  • Public channels
  • Private channels
  • Presence channels
    • The User object
• Binding and handling events
• Triggering events
• Accessing the connection socket ID
• Helper Methods
  • Getting a channel from string
  • Check if a channel has subscribed
• JavaDocs
• Library Development Environment
  • Prerequisites
  • Cloning the project
  • Eclipse Project
  • Build
  • Run the Example Application

The compiled library is available in two ways:

The pusher-java-client is available in Maven Central.

<dependencies>
    <dependency>
      <groupId>com.pusher</groupId>
      <artifactId>pusher-java-client</artifactId>
      <version>1.8.0</version>
    </dependency>
</dependencies>

dependencies {
  compile 'com.pusher:pusher-java-client:1.8.0'
}

You can download a version of the .jar directly from https://repo1.maven.org/maven2/com/pusher/pusher-java-client/

You can build the project from the source in this repository. See Library development environment for more information on build environment.

Here's the API in a nutshell.

// Create a new Pusher instance
PusherOptions options = new PusherOptions().setCluster(YOUR_APP_CLUSTER);
Pusher pusher = new Pusher(YOUR_APP_KEY, options);

pusher.connect(new ConnectionEventListener() {
    @Override
    public void onConnectionStateChange(ConnectionStateChange change) {
        System.out.println("State changed to " + change.getCurrentState() +
                           " from " + change.getPreviousState());
    }

    @Override
    public void onError(String message, String code, Exception e) {
        System.out.println("There was a problem connecting!");
    }
}, ConnectionState.ALL);

// Subscribe to a channel
Channel channel = pusher.subscribe("my-channel");

// Bind to listen for events called "my-event" sent to "my-channel"
channel.bind("my-event", new SubscriptionEventListener() {
    @Override
    public void onEvent(PusherEvent event) {
        System.out.println("Received event with data: " + event.toString());
    }
});

// Disconnect from the service
pusher.disconnect();

// Reconnect, with all channel subscriptions and event bindings automatically recreated
pusher.connect();
// The state change listener is notified when the connection has been re-established,
// the subscription to "my-channel" and binding on "my-event" still exist.

More information in reference format can be found below.

The standard constructor take an application key which you can get from the app's API Access section in the Pusher Channels dashboard.

PusherOptions options = new PusherOptions().setCluster(YOUR_APP_CLUSTER);
Pusher pusher = new Pusher(YOUR_APP_KEY, options);

If you are going to use private or presence channels then you will need to provide an Authorizer to be used when authenticating subscriptions. In order to do this you need to pass in a PusherOptions object which has had an Authorizer set.

HttpAuthorizer authorizer = new HttpAuthorizer("https://example.com/some_auth_endpoint");
PusherOptions options = new PusherOptions().setCluster(YOUR_APP_CLUSTER).setAuthorizer(authorizer);
Pusher pusher = new Pusher(YOUR_APP_KEY, options);

See the documentation on Authenticating Users for more information.

If you need finer control over the endpoint then the setHost, setWsPort and setWssPort methods can be employed.

In order to send and receive messages you need to connect to Channels.

PusherOptions options = new PusherOptions().setCluster(YOUR_APP_CLUSTER);
Pusher pusher = new Pusher(YOUR_APP_KEY, options);
pusher.connect();

Most of the functionality of this library is configured through the PusherOptions object. You configure it by calling methods with parameters on the object before passing it to the Pusher object. Below is a table containing all of the methods you can call.

The connect method is also used to re-connect in case the connection has been lost, for example if an Android device loses reception. Note that the state of channel subscriptions and event bindings will be preserved while disconnected and re-negotiated with the server once a connection is re-established.

pusher.disconnect();

After disconnection the Pusher instance will release any internally allocated resources (threads and network connections)

Implement the ConnectionEventListener interface to receive connection state change events:

PusherOptions options = new PusherOptions().setCluster(YOUR_APP_CLUSTER);
Pusher pusher = new Pusher(YOUR_APP_KEY, options);
pusher.connect(new ConnectionEventListener() {
    @Override
    public void onConnectionStateChange(ConnectionStateChange change) {
        System.out.println("State changed to " + change.getCurrentState() +
                           " from " + change.getPreviousState());
    }

    @Override
    public void onError(String message, String code, Exception e) {
        System.out.println("There was a problem connecting!");
    }
});

A series of ConnectionState members can be passed after the listener in this call to filter the states which will receive notification, e.g.

// MyConnectionEventListener is notified only of transitions to the disconnected state
pusher.connect(new MyConnectionEventListener(), ConnectionState.DISCONNECTED);

For more information see connection states.

Channels uses the concept of channels as a way of subscribing to data. They are identified and subscribed to by a simple name. Events are bound to on a channels and are also identified by name. To listen to an event you need to implemented the ChannelEventListener interface (see Binding and handling events).

As mentioned above, channel subscriptions need only be registered once per Pusher instance. They are preserved across disconnection and re-established with the server on reconnect. They should NOT be re-registered. They may, however, be registered with a Pusher instance before the first call to connect - they will be completed with the server as soon as a connection becomes available.

Channel channel = pusher.subscribe("my-channel");

If you wish to be informed when the subscription succeeds, pass an implementation of the ChannelEventListener interface:

Channel channel = pusher.subscribe("my-channel", new ChannelEventListener() {
    @Override
    public void onSubscriptionSucceeded(String channelName) {
        System.out.println("Subscribed to channel: " + channelName);
    }

    // Other ChannelEventListener methods
});

It's possible to subscribe to private channels that provide a mechanism for authenticating channel subscriptions. In order to do this you need to provide an Authorizer when creating the Pusher instance (see The Pusher constructor above).

The library provides a HttpAuthorizer implementation of Authorizer which makes an HTTP POST request to an authenticating endpoint. However, you can implement your own authentication mechanism if required.

Private channels are subscribed to as follows:

PrivateChannel privateChannel = pusher.subscribePrivate( "private-channel" );

In addition to the events that are possible on public channels a private channel exposes an onAuthenticationFailure. This is called if the Authorizer does not successfully authenticate the subscription:

PrivateChannel channel = pusher.subscribePrivate("private-channel",
    new PrivateChannelEventListener() {
        @Override
        public void onAuthenticationFailure(String message, Exception e) {
            System.out.println(
                String.format("Authentication failure due to [%s], exception was [%s]", message, e)
            );
        }

        // Other ChannelEventListener methods
    });

Presence channels are private channels which provide additional events exposing who is currently subscribed to the channel. Since they extend private channels they also need to be authenticated (see authenticating channel subscriptions).

Presence channels can be subscribed to as follows:

PresenceChannel presenceChannel = pusher.subscribePresence( "presence-channel" );

Presence channels provide additional events relating to users joining (subscribing) and leaving (unsubscribing) the presence channel. It is possible to listen to these events by implementing the PresenceChannelEventListener.

PresenceChannel channel = pusher.subscribePresence("presence-channel",
    new PresenceChannelEventListener() {
        @Override
        public void onUsersInformationReceived(String channelName, Set<User> users) {
            for (User user : users) {
                userSubscribed(channelName, user);
            }
        }

        @Override
        public void userSubscribed(String channelName, User user) {
            System.out.println(
                String.format("A new user joined channel [%s]: %s, %s",
                              channelName, user.getId(), user.getInfo())
            );

            if (user.equals(channel.getMe())) {
                System.out.println("me");
            }
        }

        @Override
        public void userUnsubscribed(String channelName, User user) {
            System.out.println(
                String.format("A user left channel [%s]: %s %s",
                              channelName, user.getId(), user.getInfo())
            );
        }

        // Other ChannelEventListener methods
    });

Note: In the Pusher Channels documentation a User may be referred to as a Member.

The User object has two main methods.

getId fetches a unique identifier for the user on the presence channel.

getInfo fetches a string representing arbitrary additional information about the user in the form of a JSON hash, e.g.

{"user_name":"Mr. User","user_score":1357}

The following example using the Gson library to handle deserialization:

String jsonInfo = user.getInfo();
Gson gson = new Gson();
UserInfo info = gson.fromJson(jsonInfo, UserInfo.class);

For more information on defining the user id and user info on the server see Implementing the auth endpoint for a presence channel documentation.

Channels now provides a 'user-id' with client events sent from the server. With presence channels, your authentication endpoint provides your user with a user-id. Previously, it was up to you to include this user-id in every client-event triggered by your clients. Now, when a client of yours triggers a client event, Channels will append their user-id to their triggered message, so that the other clients in the channel receive it. This allows you to trust that a given user really did trigger a given payload.

If you’d like to make use of this feature, you’ll need to extract the user-id from the message delivered by Channels. To do this, call getUserId() on the event payload your event handler gets called with, like so:

channel.bind("client-my-event", new SubscriptionEventListener() {
    @Override
    public void onEvent(PusherEvent event) {
        System.out.println("Received event with userId: " + event.getUserId());
    }
});

You can also instead retrieve it in the following way:

event.getProperty(“user_id”)

There are two types of events that occur on channel subscriptions.

1. Protocol related events such as those triggered when a subscription succeeds
2. Application events that have been triggered by code within your application

The ChannelEventListener is an interface that is informed of both protocol related events and application data events. A ChannelEventListener can be used when initially subscribing to a channel.

Channel channel = pusher.subscribe("my-channel", new ChannelEventListener() {
    @Override
    public void onSubscriptionSucceeded(String channelName) {
        System.out.println("Subscribed!");
    }

    @Override
    public void onEvent(PusherEvent event) {
        // Called for incoming events names "foo", "bar" or "baz"
    }
}, "foo", "bar", "baz");

The ChannelEventListener interface extends the SubscriptionEventListener interface.

Events triggered by your application are received by the onEvent method on the SubscriptionEventListener interface implementation. If you are only related to application events you can bind to events on Channel objects.

Channel channel = pusher.subscribe("my-channel");
channel.bind("my-event", new ChannelEventListener() {
    @Override
    public void onEvent(PusherEvent event) {
        // Called for incoming events named "my-event"
    }
});

The event data is accessible by calling the getData() method on the event. From there you can handle the data as you like. Since we encourage data to be in JSON here's an example that uses Gson object deserialization:

public class Example implements ChannelEventListener {
    public Example() {
        Pusher pusher = new Pusher(YOUR_APP_KEY);
        pusher.subscribe("my-channel", this);
        pusher.connect();
    }

    @Override
    public void onEvent(PusherEvent event) {
        Gson gson = new Gson();
        EventExample exampleEvent = gson.fromJson(event.getData(), EventExample.class);
    }
}

class EventExample {
    private int value1 = 1;
    private String value2 = "abc";
    private transient int value3 = 3;

    EventExample() { }
}

You can unbind from an event:

channel.unbind("my_event", listener);

public class Example implements ChannelEventListener {
    private final Pusher pusher;
    private final Channel channel;

    public Example() {
        pusher = new Pusher(YOUR_APP_KEY);
        channel = pusher.subscribe("my-channel", this, "my_event");

        pusher.connect();
    }

    public void listenToOtherEvent() {
        channel.bind("my_other_event", this);
    }

    public void stopListeningToOtherEvent() {
        channel.unbind("my_other_event", this);
    }
}

Once a private or presence subscription has been authorized (see authenticating users) and the subscription has succeeded, it is possible to trigger events on those channels.

channel.trigger("client-myEvent", "{\"myName\":\"Bob\"}");

Events triggered by clients are called client events. Because they are being triggered from a client which may not be trusted there are a number of enforced rules when using them. Some of these rules include:

• Event names must have a client- prefix
• Rate limits
• You can only trigger an event when the subscription has succeeded

For full details see the client events documentation.

PrivateChannel channel = pusher.subscribePrivate("private-channel",
    new PrivateChannelEventListener() {
        @Override
        public void onSubscriptionSucceeded(String channelName) {
            channel.trigger("client-myEvent", "{\"myName\":\"Bob\"}");
        }

        // Other PrivateChannelEventListener methods
    });

Once connected you can access a unique identifier for the current client's connection. This is known as the socket_id.

You can access the value once the connection has been established as follows:

String socketId = pusher.getConnection().getSocketId();

For more information on how and why there is a socket_id see the documentation on authenticating users and excluding recipients.

Channel channel = pusher.getChannel("my-channel");

The library will raise an exception if the parameter to Pusher#getPrivateChannel is prefixed with "private-" or "presence-".

PrivateChannel channel = pusher.getPrivateChannel("private-channel");

The library will raise an exception if the parameter to Pusher#getPrivateChannel is not prefixed with "private-".

PresenceChannel channel = pusher.getPresenceChannel("presence-channel");

The library will raise an exception if the parameter to Pusher#getPresenceChannel is not prefixed with "presence-".

Channel channel = pusher.getChannel("my-channel");
channel.isSubscribed(); // => `true`/`false`

The JavaDocs can be found here: https://pusher.github.com/pusher-websocket-java/

If you'd like to tweak this library there are ways to use your local code rather than the official. This is a rough guide on how to do so.

• A Java Virtual Machine.
• Gradle, the build system used for the project, is downloaded by the Gradle Wrapper (gradlew) which is included in the repo.
• On Windows ./gradlew.bat should be used, on Linux ./gradle.

• Clone the project: git clone https://github.com/pusher/pusher-websocket-java
• Change to the top level directory for the project: cd pusher-websocket-java

• In your app project's settings.gradle add the following lines:

include ':pusher-websocket-java'
project(':pusher-websocket-java').projectDir = new File('<PATH_TO_THIS_PROJECT>/pusher-websocket-java')

• Add the following line to your application's build.gradle where you would normally add the actual pusher-websocket-java SDK:

dependencies {
    compile project(':pusher-websocket-java')
}

Assuming you are using Eclipse, follow these steps:

• Run gradlew eclipse. This will generate the .classpath and .project files
• You can now load the project in Eclipse by navigating to Import project and pointing it to the root directory of the existing project.

From the top level directory execute:

• gradlew test to execute the tests.
• gradlew javadoc to generate the JavaDoc. The docs will be output to the build/docs/javadoc/ directory.
• gradlew assemble assemble all artifacts but does not run any tests.
• gradlew build to build all jars and execute all tests & verification. The jars will be output to the build/libs directory.
• gradlew createPublishTarget uploadArchives to upload all artifacts. This task requires some properties to be set, see below.
• gradlew publishGhPages to upload JavaDocs to gh-pages. This task requires some properties to be set, see below.

There are several build properties used for authentication. These should be set either in ~/.gradle/gradle.properties using the format property=value or can be passed via command line as -Pprop=val.

The properties used for the build are:

• maven.username - the username used for Maven deployment authentication
• maven.password - the password used for Maven deployment authentication
• github.username - the username used for GitHub authentication
• github.password - the password used for GitHub authentication

After running gradlew clean assemble change to the build/libs directory and run java -jar pusher-java-client-<version>-jar-with-dependencies.jar. This will run the example application.

By default the example will connect to a sample application and subscribe to the channel my-channel, listening to events on my-event. If you want to change these defaults, they can be specified on the command line:

java -jar pusher-java-client-<version>-jar-with-dependencies.jar [appKey] [channelName] [eventName]