Durable Sessions

When a server restarts, all in-memory state is lost — room memberships, broadcaster subscriptions, metadata. Durable sessions persist this state and restore it automatically when a client reconnects.

How It Works

The durable session lifecycle is driven by the DurableSessionInterceptor:

1. First connect — the interceptor creates a DurableSession, saves it via the SessionStore, and returns a token to the client in the X-Atmosphere-Session-Token response header.
2. During the connection — the interceptor registers a disconnect listener that captures the resource’s current rooms and broadcaster subscriptions into the session store.
3. Reconnect — if the client sends the token back in the X-Atmosphere-Session-Token request header (or as a query parameter), the interceptor restores the session: it re-joins the resource to its previous broadcasters and rooms using BroadcasterFactory.lookup() and RoomManager.room().join().
4. Expiration — a background thread periodically calls store.removeExpired(ttl) to clean up sessions that have not been seen within the configured TTL (default: 24 hours).

The DurableSession Record

DurableSession is a Java record that captures the full state snapshot:

public record DurableSession(
        String token,
        String resourceId,
        Set<String> rooms,
        Set<String> broadcasters,
        Map<String, String> metadata,
        Instant createdAt,
        Instant lastSeen
) { }

It provides factory and copy methods:

• DurableSession.create(token, resourceId) — creates a new session with the current timestamp
• withRooms(Set<String>) — returns a copy with updated rooms
• withBroadcasters(Set<String>) — returns a copy with updated broadcaster IDs
• withMetadata(Map<String, String>) — returns a copy with updated metadata
• withResourceId(String) — returns a copy with a new resource ID and refreshed lastSeen

The SessionStore SPI

The SessionStore interface defines the persistence contract:

public interface SessionStore {
    void save(DurableSession session);
    Optional<DurableSession> restore(String token);
    void remove(String token);
    void touch(String token);
    List<DurableSession> removeExpired(Duration ttl);
    default void close() { }
}

Three implementations are provided:

Implementation	Module	Description
InMemorySessionStore	durable-sessions	ConcurrentHashMap-backed, for testing and development. Sessions are lost on restart.
SqliteSessionStore	durable-sessions-sqlite	Embedded SQLite database, zero-config. Perfect for single-node deployments.
RedisSessionStore	durable-sessions-redis	Lettuce-backed Redis store. Shared across cluster nodes.

InMemorySessionStore

The default store when no other is configured. Uses a ConcurrentHashMap and is only suitable for development and testing since sessions are lost when the JVM exits.

SqliteSessionStore

Zero-configuration embedded storage. Just add the dependency:

<dependency>
    <groupId>org.atmosphere</groupId>
    <artifactId>atmosphere-durable-sessions-sqlite</artifactId>
    <version>LATEST</version> <!-- check Maven Central for latest -->
</dependency>

SqliteSessionStore creates a SQLite database file with a durable_sessions table using WAL journal mode for concurrent read performance. Three constructors are available:

var store = new SqliteSessionStore();                           // default: atmosphere-sessions.db
var store = new SqliteSessionStore(Path.of("/data/sessions")); // custom path
var store = SqliteSessionStore.inMemory();                     // for testing

Parent directories are created automatically if they do not exist.

RedisSessionStore

For clustered deployments where multiple nodes need access to the same session data:

<dependency>
    <groupId>org.atmosphere</groupId>
    <artifactId>atmosphere-durable-sessions-redis</artifactId>
    <version>LATEST</version> <!-- check Maven Central for latest -->
</dependency>

RedisSessionStore uses Lettuce and stores sessions as JSON hashes with a TTL.

Spring Boot Integration

The atmosphere-spring-boot-starter auto-configures durable sessions when a SessionStore bean is present. The sample application at samples/spring-boot-durable-sessions/ demonstrates the full setup.

SessionStoreConfig.java

From samples/spring-boot-durable-sessions/:

@Configuration
public class SessionStoreConfig {

    @Bean
    public SessionStore sessionStore() {
        return new SqliteSessionStore(Path.of("data/sessions.db"));
    }
}

That is the only configuration needed. The auto-configuration picks up the SessionStore bean and registers the DurableSessionInterceptor automatically.

Chat.java

The @ManagedService class does not need any durable-session-specific code. The interceptor handles everything transparently:

@ManagedService(path = "/atmosphere/chat", atmosphereConfig = MAX_INACTIVE + "=120000")
public class Chat {

    private final Logger logger = LoggerFactory.getLogger(Chat.class);

    @Inject
    private AtmosphereResource r;

    @Inject
    private AtmosphereResourceEvent event;

    @Ready
    public void onReady() {
        logger.info("Client {} connected (session will persist across restarts)", r.uuid());
    }

    @Disconnect
    public void onDisconnect() {
        if (event.isCancelled()) {
            logger.info("Client {} unexpectedly disconnected — session saved",
                    event.getResource().uuid());
        } else {
            logger.info("Client {} closed — session saved",
                    event.getResource().uuid());
        }
    }

    @org.atmosphere.config.service.Message(
            encoders = {JacksonEncoder.class},
            decoders = {JacksonDecoder.class})
    public Message onMessage(Message message) {
        logger.info("{} says: {}", message.getAuthor(), message.getMessage());
        return message;
    }
}

DurableSessionsApplication.java

The main class is a standard Spring Boot application:

@SpringBootApplication
public class DurableSessionsApplication {
    public static void main(String[] args) {
        SpringApplication.run(DurableSessionsApplication.class, args);
    }
}

Programmatic Registration

If you are not using Spring Boot auto-configuration, register the interceptor manually:

var store = new SqliteSessionStore(Path.of("data/sessions.db"));
framework.interceptor(new DurableSessionInterceptor(store));

The constructor also accepts optional TTL and save interval parameters:

var interceptor = new DurableSessionInterceptor(
    store,
    Duration.ofHours(24),   // session TTL
    Duration.ofMinutes(1)   // cleanup interval
);
framework.interceptor(interceptor);

The DurableSessionInterceptor in Detail

The interceptor runs at BEFORE_DEFAULT priority, so it executes before application interceptors.

On each inspect() call:

1. It checks for an X-Atmosphere-Session-Token header (or query parameter).
2. If a token is found and the session exists in the store, it restores broadcaster subscriptions via BroadcasterFactory.lookup() and room memberships via RoomManager.room().join(). The session is updated with the new resource ID.
3. If no token is found (or the session expired), a new DurableSession is created with a UUID token and saved to the store. The token is returned in the response header.
4. In both cases, a disconnect listener is registered that captures the resource’s current rooms and broadcasters into the store when the connection closes.

The interceptor guards against double-save when both onDisconnect and onClose fire for the same resource by tracking resource UUIDs in a ConcurrentHashMap.newKeySet().

ConversationPersistence for AI Memory

Separate from session state, the ConversationPersistence SPI (in the atmosphere-ai module) persists AI conversation history so that users can resume conversations across server restarts:

public interface ConversationPersistence {
    Optional<String> load(String conversationId);
    void save(String conversationId, String data);
    void remove(String conversationId);
    default boolean isAvailable() { return true; }
}

Two implementations are provided:

Implementation	Module
SqliteConversationPersistence	durable-sessions-sqlite
RedisConversationPersistence	durable-sessions-redis

These share the same backend connections as the corresponding SessionStore implementations. The PersistentConversationMemory class handles serialization and sliding-window logic on top of the persistence SPI.

Combining with Clustering

Durable sessions and clustering serve different purposes and work well together:

• Clustering (Chapter 16) ensures messages reach all nodes during normal operation
• Durable sessions ensure clients can reconnect after a node failure or restart and resume their previous state

For a fully resilient deployment, combine a clustered broadcaster with RedisSessionStore so that session state is accessible from any node:

@Bean
public SessionStore sessionStore() {
    return new RedisSessionStore("redis://localhost:6379");
}

Summary

• The SessionStore SPI has three implementations: InMemorySessionStore (testing), SqliteSessionStore (single node), and RedisSessionStore (clustered)
• DurableSessionInterceptor transparently saves and restores room memberships and broadcaster subscriptions using the X-Atmosphere-Session-Token header
• DurableSession is a Java record capturing token, resource ID, rooms, broadcasters, metadata, and timestamps
• Spring Boot auto-configures the interceptor when a SessionStore bean is present
• ConversationPersistence provides a parallel SPI for persisting AI conversation history
• No application code changes are needed — the interceptor works transparently with any @ManagedService

Next up: Chapter 18: Observability covers Micrometer metrics, OpenTelemetry tracing, and health checks.