# Getting started: LiveObjects in Java

<Aside data-type='note'>
**Building with LiveObjects?** Help shape its future by [sharing your use case](https://44qpp.share.hsforms.com/2fZobHQA1ToyRfB9xqZYQmQ).
</Aside>

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.
* Use the [PathObject API](https://ably.com/docs/liveobjects/concepts/path-object.md) to access objects on a channel.
* Create, update and subscribe to changes on LiveObjects data structures: [LiveMap](https://ably.com/docs/liveobjects/map.md) and [LiveCounter](https://ably.com/docs/liveobjects/counter.md).

## Authentication 

An [API key](https://ably.com/docs/auth.md#api-keys) is required to authenticate with Ably. API keys are used either to authenticate directly with Ably using [basic authentication](https://ably.com/docs/auth/basic.md), or to generate tokens for untrusted clients using [token authentication](https://ably.com/docs/auth/token.md).

<Aside data-type='important'>
The examples use [basic authentication](https://ably.com/docs/auth/basic.md) to demonstrate features for convenience. In your own applications, basic authentication should never be used on the client-side as it exposes your Ably API key. Instead use [token authentication](https://ably.com/docs/auth/token.md).
</Aside>

[Sign up](https://ably.com/sign-up) for a free account and create your own API key in the [dashboard](https://ably.com/dashboard) or use the [Control API](https://ably.com/docs/platform/account/control-api.md) to create an API key programmatically.

API keys and tokens have a set of [capabilities](https://ably.com/docs/auth/capabilities.md) 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 channel 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](https://ably.com/docs/auth/capabilities.md) to allow full read and write access.

## Install Ably Pub/Sub SDK 

LiveObjects is available as part of the Ably Pub/Sub SDK via the dedicated Objects plugin. The plugin is discovered from the classpath at runtime. No code registration is needed; adding the dependency is enough.

### Install for Maven 

```xml
<dependency>
    <groupId>io.ably</groupId>
    <artifactId>ably-java</artifactId>
    <version>1.8.1</version>
</dependency>
<dependency>
    <groupId>io.ably</groupId>
    <artifactId>liveobjects</artifactId>
    <version>1.8.1</version>
    <scope>runtime</scope>
</dependency>
```

### Install for Gradle 

```java
implementation 'io.ably:ably-java:1.8.1'
runtimeOnly 'io.ably:liveobjects:1.8.1'
```

For `Android` platform, use `ably-android` instead of `ably-java`

```java
implementation 'io.ably:ably-android:1.8.1'
runtimeOnly 'io.ably:liveobjects:1.8.1'
```

## Instantiate a client 

Instantiate an Ably Realtime client from the Pub/Sub SDK:

<Code>

### Java

```
AblyRealtime realtime = new AblyRealtime(new ClientOptions("your-api-key"));
```
</Code>

A [`ClientOptions`](https://ably.com/docs/api/realtime-sdk.md#client-options) 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. The LiveObjects plugin is picked up automatically when `io.ably:liveobjects` is on the runtime classpath. If the plugin is missing, reading the `channel.object` field is still safe, but calling any method on it (for example `channel.object.get()`) fails with error code `40019` and a message telling you which dependency to add.

## Create a channel 

LiveObjects is managed and persisted on [channels](https://ably.com/docs/channels.md). To use LiveObjects, you must first create a channel with the correct [channel mode flags](https://ably.com/docs/channels/options.md#modes):

* `OBJECT_SUBSCRIBE` - required to access objects on a channel.
* `OBJECT_PUBLISH` - required to create and modify objects on a channel.

<Aside data-type='note'>
When you provide an explicit `modes` field for a channel, you override the set of [default modes](https://ably.com/docs/channels/options.md#modes) used for that channel. So, if you're using the channel for anything in addition to LiveObjects, you need to ensure that you also include the other modes required by the features you are using.
</Aside>

<Code>

### Java

```
ChannelOptions opts = new ChannelOptions();
opts.modes = new ChannelMode[] {
    ChannelMode.object_publish,
    ChannelMode.object_subscribe
};
Channel channel = realtime.channels.get("test-channel", opts);
```
</Code>

## Get the channel object 

The [`channel.object`](https://ably.com/docs/api/realtime-sdk/channels.md#object) field gives access to the LiveObjects API for a channel.

Use `channel.object.get()` to obtain the channel object. The channel object is a [`LiveMap`](https://ably.com/docs/liveobjects/map.md) that always exists on a channel and acts as the top-level entry point for accessing and persisting objects. It is returned as a [`LiveMapPathObject`](https://ably.com/docs/liveobjects/concepts/path-object.md#get), which provides a path-based API for accessing and manipulating the object hierarchy.

Every LiveObjects mutation is asynchronous: `channel.object.get()` returns a `CompletableFuture<LiveMapPathObject>` that completes once the LiveObjects state is synchronized with the Ably system; reads are synchronous and local. The **recommended** pattern is to compose these futures rather than block on them: hold the future returned by `get()` and chain each step onto it:

<Code>

### Java

```
// Recommended: keep the future reference explicit and compose it
CompletableFuture<LiveMapPathObject> objectFuture = channel.object.get();

// Get the object, then create your first object - without blocking.
// thenCompose sequences dependent operations (each returns its own future);
// finish with thenRun/exceptionally.
objectFuture
    .thenCompose(rootObject -> rootObject.set("visits", LiveMapValue.of(LiveCounter.create(0))))
    .thenRun(() -> System.out.println("Channel object ready and counter created"))
    .exceptionally(err -> { System.err.println("Failed to set up objects: " + err); return null; });
```
</Code>

<Aside data-type='important'>
`.join()` blocks the calling thread until the future completes. It is fine for scripts, tests, and learning. But, in production code, it's recommended to compose the future with `thenApply`/`thenCompose`/`thenAccept`/`exceptionally` as shown above. Also, running blocking code inside an ably event listener callback causes deadlock.
</Aside>

The remaining steps in this guide call `.join()` to keep each example short and focused on the LiveObjects API. It blocks until the operation completes and returns the result directly:

<Code>

### Java

```
// For brevity, the rest of this guide blocks with join()
LiveMapPathObject rootObject = channel.object.get().join();
```
</Code>

<Aside data-type='note'>
Calling `channel.object.get()` implicitly attaches to the channel if it's not already attached. You don't need to manually call `channel.attach()` before getting the object.
</Aside>

## Create and assign objects 

You can create and assign objects using the `LiveMap.create()` and `LiveCounter.create()` static methods. These methods return a description of the object to create; the actual object is created when you assign it to a key with `set()`. Every value passed to `set()` is wrapped in `LiveMapValue.of(...)`:

<Code>

### Java

```
// Create a LiveCounter with initial value 0
LiveCounter visits = LiveCounter.create(0);

// Assign it to the 'visits' key on the channel object
rootObject.set("visits", LiveMapValue.of(visits)).join();

// Create a LiveMap with initial entries
LiveMap reactions = LiveMap.create(Map.of(
    "likes", LiveMapValue.of(0),
    "hearts", LiveMapValue.of(0)));

// Assign it to the 'reactions' key on the channel object
rootObject.set("reactions", LiveMapValue.of(reactions)).join();

// Infer types for the assigned objects
LiveCounterPathObject visitsCounter = rootObject.get("visits").asLiveCounter();
LiveMapPathObject reactionsMap = rootObject.get("reactions").asLiveMap();
```
</Code>

`rootObject.get(key)` returns a general [`PathObject`](https://ably.com/docs/liveobjects/concepts/path-object.md) that doesn't yet know the type of the value it points to. Call one of the `as*` methods, such as `asLiveCounter()` or `asLiveMap()`, to work with the value as a specific type. These casts are always safe to call: they never throw an exception, even if the value at the path has a different type. Learn more about [Type inference](https://ably.com/docs/liveobjects/typing.md#type-inference).

<Aside data-type='note'>
You can create deeply nested structures in a single operation by nesting `LiveMap.create()` and `LiveCounter.create()` calls.
</Aside>

## Subscribe to updates 

Subscribe to realtime updates using the `subscribe()` method on a `PathObject`. You will be notified when the object at that path is updated by other clients or by you:

<Code>

### Java

```
// Subscribe to counter updates
visitsCounter.subscribe(event ->
    System.out.println("Visits counter updated: " + event.getObject().asLiveCounter().value()));

// Subscribe to map updates
reactionsMap.subscribe(event ->
    System.out.println("Reactions updated: " + event.getObject().compactJson()));
```
</Code>

The subscription callback receives an event that exposes:
- `getObject()`: A `PathObject` pointing to the path where the change occurred
- `getMessage()`: The `ObjectMessage` that carried the operation that led to the change (nullable)

The `subscribe()` method also returns a `Subscription` object. When you no longer want to receive updates, call `subscription.unsubscribe()` on it:

<Code>

### Java

```
// Keep the Subscription returned by subscribe()
Subscription subscription = visitsCounter.subscribe(event ->
    System.out.println("Visits counter updated: " + event.getObject().asLiveCounter().value()));

// Later, stop receiving updates
subscription.unsubscribe();
```
</Code>

## Update objects 

Update objects using mutation methods on `PathObject`. All subscribers (including you) will be notified of the changes:

<Code>

### Java

```
// Update counter
visitsCounter.increment(5).join();
// console: Visits counter updated: 5.0

visitsCounter.decrement(2).join();
// console: Visits counter updated: 3.0

// Update map
reactionsMap.set("likes", LiveMapValue.of(10)).join();
// console: Reactions updated: {"likes":10.0,"hearts":0.0}

reactionsMap.set("hearts", LiveMapValue.of(5)).join();
// console: Reactions updated: {"likes":10.0,"hearts":5.0}

reactionsMap.remove("likes").join();
// console: Reactions updated: {"hearts":5.0}
```
</Code>

<Aside data-type='note'>
Mutation methods send operations to the Ably system and apply changes locally as soon as the operations are acknowledged. Once the returned `CompletableFuture` completes, the operation has been applied locally and you can read the updated state immediately. You will also be notified via subscription when the object is updated.
</Aside>

## Next steps 

This quickstart introduced the basic concepts of LiveObjects and demonstrated how the path-based API works. The next steps are to:

* Learn about the [PathObject](https://ably.com/docs/liveobjects/concepts/path-object.md) and [Instance](https://ably.com/docs/liveobjects/concepts/instance.md) APIs.
* Read more about [LiveCounter](https://ably.com/docs/liveobjects/counter.md) and [LiveMap](https://ably.com/docs/liveobjects/map.md).
* Learn about [Objects Lifecycle Events](https://ably.com/docs/liveobjects/lifecycle.md).
* Learn about [Type inference](https://ably.com/docs/liveobjects/typing.md) for your LiveObjects.

## Related Topics

- [JavaScript](https://ably.com/docs/liveobjects/quickstart/javascript.md): A getting started guide to learn the basics of integrating the Ably LiveObjects product into your JavaScript application.
- [Swift](https://ably.com/docs/liveobjects/quickstart/swift.md): A quickstart guide to learn the basics of integrating the Ably LiveObjects product into your Swift application.

## Documentation Index

To discover additional Ably documentation:

1. Fetch [llms.txt](https://ably.com/llms.txt) for the canonical list of available pages.
2. Identify relevant URLs from that index.
3. Fetch target pages as needed.

Avoid using assumed or outdated documentation paths.