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This guide shows how to integrate Ably LiveObjects into your Java application. You will learn how to:
  • Create an Ably account and get an API key for authentication.
  • Install the Ably Pub/Sub SDK.
  • Create a channel with LiveObjects functionality enabled.
  • Create, update and subscribe to changes on LiveObjects data structures: LiveMap and LiveCounter.

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Authentication

An API key is required to authenticate with Ably. API keys are used either to authenticate directly with Ably using basic authentication, or to generate tokens for untrusted clients using token authentication. Sign up for a free account and create your own API key in the dashboard or use the Control API to create an API key programmatically. API keys and tokens have a set of capabilities assigned to them that specify which operations can be performed on which resources. The following capabilities are available for LiveObjects:
  • object-subscribe - grants clients read access to LiveObjects, allowing them to get the root object and subscribe to updates.
  • object-publish - grants clients write access to LiveObjects, allowing them to perform mutation operations on objects.
To use LiveObjects, an API key must have at least the object-subscribe capability. With only this capability, clients will have read-only access, preventing them from calling mutation methods on LiveObjects. For the purposes of this guide, make sure your API key includes both object-subscribe and object-publish capabilities to allow full read and write access.

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Install Ably Pub/Sub SDK

LiveObjects is available as part of the Ably Pub/Sub SDK via the dedicated Objects plugin.

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Install for Maven:

<dependency>
    <groupId>io.ably</groupId>
    <artifactId>ably-java</artifactId>
    <version>1.3.0</version>
</dependency>
<dependency>
    <groupId>io.ably</groupId>
    <artifactId>liveobjects</artifactId>
    <version>1.3.0</version>
</dependency>

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Install for Gradle:

implementation 'io.ably:ably-java:1.3.0'
implementation 'io.ably:liveobjects:1.3.0'
For Android platform, use ably-android instead of ably-java 
implementation 'io.ably:ably-android:1.3.0'

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Instantiate a client

Instantiate an Ably Realtime client from the Pub/Sub SDK, providing the Objects plugin: 
AblyRealtime realtime = new AblyRealtime(new ClientOptions("ABLY_KEY"));
A ClientOptions object may be passed to the Pub/Sub SDK instance to further customize the connection, however at a minimum you must set an API key and provide an Objects plugin so that the client can use LiveObjects functionality.

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Create a channel

LiveObjects is managed and persisted on channels. To use LiveObjects, you must first create a channel with the correct channel mode flags:
  • OBJECT_SUBSCRIBE - required to access objects on a channel.
  • OBJECT_PUBLISH - required to create and modify objects on a channel.
ChannelOptions opts = new ChannelOptions();
opts.modes = new ChannelMode[] {
    ChannelMode.object_publish,
    ChannelMode.object_subscribe
};
ChannelBase channel = realtime.channels.get("test-channel", opts);

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Get root object

The channel.getObjects method gives access to the LiveObjects API for a channel. Use it to get the root object, which is the entry point for accessing and persisting objects on a channel. The root object is a LiveMap instance that always exists on a channel and acts as the top-level node in your object tree. You can get the root object using the getRoot() method of LiveObjects: 
// The root is returned once the LiveObjects state is synchronized with the Ably system.
// `getRoot` Implicitly attaches channel if it's in a INITIALIZED state
RealtimeObjects objects = channel.getObjects();
LiveMap root = objects.getRoot(); // blocks current thread till result is returned
The above getRoot() method is blocking in nature so it’s recommended to use getRootAsync() instead 
RealtimeObjects objects = channel.getObjects();
objects.getRootAsync(new ObjectsCallback<LiveMap>() {
    @Override
    public void onSuccess(LiveMap root) {
        // Successfully retrieved the root LiveMap
        System.out.println("Root object retrieved: " + root);
        // You can now use the root object to create and manage other objects
    }

    @Override
    public void onError(AblyException exception) {
        // Handle errors (network issues, authentication failures, etc.)
        System.err.println("Failed to get root object: " + exception.getMessage());
    }
});

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Create objects

You can create new objects using dedicated methods of the LiveObjects API at channel.getObjects(). To persist them on a channel and share them between clients, you must assign objects to a parent LiveMap instance connected to the root object. The root object itself is a LiveMap instance, so you can assign objects to the root and start building your object tree from there. 
LiveCounter visitsCounter = objects.createCounter();
LiveMap reactionsMap = objects.createMap();

root.set("visits", LiveMapValue.of(visitsCounter));
root.set("reactions", LiveMapValue.of(reactionsMap));

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Subscribe to updates

Subscribe to realtime updates to objects on a channel. You will be notified when an object is updated by other clients or by you. 
visitsCounter.subscribe((counterUpdate) ->
    System.out.println("Visits counter updated: " +
        counterUpdate.getUpdate().getAmount());
);

reactionsMap.subscribe((mapUpdate) -> {
    System.out.println("Reactions map updated: " + mapUpdate.getUpdate());
    System.out.println("Reactions map updated: " + reactionsMap.entries());
});

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Update objects

Update objects using mutation methods. All subscribers (including you) will be notified of the changes when you update an object: 
visitsCounter.increment(5); // counter updated: 5
visitsCounter.decrement(2); // counter updated: 3

reactionsMap.set("like", LiveMapValue.of(10)); // {"like": 10}
reactionsMap.set("love", LiveMapValue.of(5)); // {"like": 10}, {"love": 5}
reactionsMap.remove("like"); // {"love": 5}

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Next steps

This quickstart introduced the basic concepts of LiveObjects and demonstrated how it works. The next steps are to:

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