Pusher client library for Java targeting general Java and Android | owner=@zmarkan
Java
Latest commit a51b9dc Feb 24, 2017 @zmarkan zmarkan committed on GitHub Merge pull request #138 from pusher/emitchel-feature/trigger-fix
Removing the requirement to trigger with JSON objects as data (same as the Swift library)

README.md

Pusher Java Client

Build Status

Pusher client library for Java targeting Android and general Java.

TOC

This README covers the following topics:

Installation

The compiled library is available in two ways:

Maven

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

<dependencies>
    <dependency>
      <groupId>com.pusher</groupId>
      <artifactId>pusher-java-client</artifactId>
      <version>1.4.0</version>
    </dependency>
</dependencies>

Gradle

dependencies {
  compile 'com.pusher:pusher-java-client:1.4.0'
}

Download

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

Source

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

API Overview

Here's the API in a nutshell.

// Create a new Pusher instance
Pusher pusher = new Pusher(YOUR_APP_KEY);

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(String channel, String event, String data) {
        System.out.println("Received event with data: " + data);
    }
});

// Disconnect from the service (or become disconnected my network conditions)
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 Pusher constructor

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

Pusher pusher = new Pusher(YOUR_APP_KEY);

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

See the documentation on Authenticating Users for more information.

You can also specify the Pusher cluster you wish to connect to on the PusherOptions, e.g.

options.setCluster("eu");

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

Connecting

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

Pusher pusher = new Pusher(YOUR_APP_KEY);
pusher.connect();

Reconnecting

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.

Disconnecting

pusher.disconnect();

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

Listening to connection events

Implement the ConnectionEventListener interface to receive connection state change events:

Pusher pusher = new Pusher(YOUR_APP_KEY);
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.

Subscribing to channels

Pusher 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.

Public channels

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
});

Private channels

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

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 onUserInformationReceived(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
    });

The User object

Note: In the Pusher 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.

Binding and handling events

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

ChannelEventListener

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(String channelName, String eventName, String data) {
        // Called for incoming events names "foo", "bar" or "baz"
    }
}, "foo", "bar", "baz");

The ChannelEventListener interface extends the SubscriptionEventListener interface.

SubscriptionEventListener

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(String channelName, String eventName, String data) {
        // Called for incoming events named "my-event"
    }
});

The event data will be passed as the third parameter to the onEvent method. 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(String channelName, String eventName, String data) {
        Gson gson = new Gson();
        EventExample exampleEvent = gson.fromJson(data, EventExample.class);
    }
}

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

    EventExample() { }
}

Unbinding event listeners

You can unbind from an event:

channel.unbind("my_event", listener);

Example

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);
    }
}

Triggering events

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
    });

Accessing the connection socket ID

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.

Helper Methods

Getting a channel from string

Basic channels

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

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

Private channels

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

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

Presence channels

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

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

Check if a channel has subscribed

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

JavaDocs

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

Library Development Environment

Prerequisites

  • 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.

Cloning the project

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

Eclipse Project

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.

Build

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.

Build Properties

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

Run the Example Application

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]