JarCastingEventflit Java Client
Eventflit client library for Java targeting Android and general Java.
TOC
This README covers the following topics:
- Installation
- API Overview
- The Eventflit constructor
- Connecting
- Reconnecting
- Disconnecting
- Listening to connection events
- Subscribing to channels
- Binding and handling events
- Triggering events
- Accessing the connection socket ID
- Helper Methods
- JavaDocs
- Library Development Environment
Installation
The compiled library is available in two ways:
Maven
The eventflit-java-client is available in Maven Central.
<dependencies>
<dependency>
<groupId>com.eventflit</groupId>
<artifactId>eventflit-java-client</artifactId>
<version>0.1.0</version>
</dependency>
</dependencies>
Gradle
dependencies {
compile 'com.eventflit:eventflit-java-client:0.1.0'
}
Download
You can download a version of the .jar directly from http://repo1.maven.org/maven2/com/eventflit/eventflit-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 Eventflit instance
EventflitOptions options = new EventflitOptions().setCluster(YOUR_APP_CLUSTER);
Eventflit eventflit = new Eventflit(YOUR_APP_KEY, options);
eventflit.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 = eventflit.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)
eventflit.disconnect();
// Reconnect, with all channel subscriptions and event bindings automatically recreated
eventflit.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 Eventflit constructor
The standard constructor take an application key which you can get from the app's API Access section in the Eventflit dashboard.
EventflitOptions options = new EventflitOptions().setCluster(YOUR_APP_CLUSTER);
Eventflit eventflit = new Eventflit(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 EventflitOptions object which has had an Authorizer set.
HttpAuthorizer authorizer = new HttpAuthorizer("http://example.com/some_auth_endpoint");
EventflitOptions options = new EventflitOptions().setCluster(YOUR_APP_CLUSTER).setAuthorizer(authorizer);
Eventflit eventflit = new Eventflit(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.
Connecting
In order to send and receive messages you need to connect to Eventflit.
EventflitOptions options = new EventflitOptions().setCluster(YOUR_APP_CLUSTER);
Eventflit eventflit = new Eventflit(YOUR_APP_KEY, options);
eventflit.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
eventflit.disconnect();
After disconnection the Eventflit 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:
EventflitOptions options = new EventflitOptions().setCluster(YOUR_APP_CLUSTER);
Eventflit eventflit = new Eventflit(YOUR_APP_KEY, options);
eventflit.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
eventflit.connect(new MyConnectionEventListener(), ConnectionState.DISCONNECTED);
For more information see connection states.
Subscribing to channels
Eventflit 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 Eventflit 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 Eventflit 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 = eventflit.subscribe("my-channel");
If you wish to be informed when the subscription succeeds, pass an implementation of the ChannelEventListener interface:
Channel channel = eventflit.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 Eventflit instance (see The Eventflit 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 = eventflit.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 = eventflit.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 = eventflit.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 = eventflit.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 Eventflit 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.
- Protocol related events such as those triggered when a subscription succeeds
- 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 = eventflit.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 = eventflit.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() {
Eventflit eventflit = new Eventflit(YOUR_APP_KEY);
eventflit.subscribe("my-channel", this);
eventflit.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 Eventflit eventflit;
private final Channel channel;
public Example() {
eventflit = new Eventflit(YOUR_APP_KEY);
channel = eventflit.subscribe("my-channel", this, "my_event");
eventflit.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 = eventflit.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 = eventflit.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 = eventflit.getChannel("my-channel");
The library will raise an exception if the parameter to Eventflit#getPrivateChannel is prefixed with "private-" or "presence-".
Private channels
PrivateChannel channel = eventflit.getPrivateChannel("private-channel");
The library will raise an exception if the parameter to Eventflit#getPrivateChannel is not prefixed with "private-".
Presence channels
PresenceChannel channel = eventflit.getPresenceChannel("presence-channel");
The library will raise an exception if the parameter to Eventflit#getPresenceChannel is not prefixed with "presence-".
Check if a channel has subscribed
Channel channel = eventflit.getChannel("my-channel");
channel.isSubscribed(); // => `true`/`false`
JavaDocs
The JavaDocs can be found here: http://eventflit.github.com/eventflit-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.batshould be used, on Linux./gradle.
- On Windows
Cloning the project
- Clone the project:
git clone https://github.com/eventflit/eventflit-java-client - Change to the top level directory for the project:
cd eventflit-java-client
Eclipse Project
Assuming you are using Eclipse, follow these steps:
- Run
gradlew eclipse. This will generate the.classpathand.projectfiles - You can now load the project in Eclipse by navigating to
Import projectand pointing it to the root directory of the existing project.
Build
From the top level directory execute:
gradlew testto execute the tests.gradlew javadocto generate the JavaDoc. The docs will be output to thebuild/docs/javadoc/directory.gradlew assembleassemble all artifacts but does not run any tests.gradlew buildto build all jars and execute all tests & verification. The jars will be output to thebuild/libsdirectory.gradlew createPublishTarget uploadArchivesto upload all artifacts. This task requires some properties to be set, see below.gradlew publishGhPagesto upload JavaDocs togh-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 authenticationmaven.password- the password used for Maven deployment authenticationgithub.username- the username used for GitHub authenticationgithub.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 eventflit-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 eventflit-java-client-<version>-jar-with-dependencies.jar [appKey] [channelName] [eventName]
