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Java API for RESTful Web Services 2.1 Released

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JAX-RS 2.1 Java API for RESTful Web Services  was released this week. According to Santiago Pericas-Geertsen, principal member of technical staff at Oracle and specifications lead for the JSR, JAX-RS 2.1 will include support for server-sent events, JSON-B and improved support for JSON-P. The API will also have a reactive extension to the client API, with built-in support for Java 8 CompletionStage and an extension point for other reactive APIs like RxJava.

According to the JAX-RS 2.1 specs, the goals for the release include annotations for POJOs, flexible API with high-level support for common HTTP usage patterns and applications including WebDAV and the Atom Publishing Protocol. The API will support various HTTP entity body content types, servlet containers and JAX-WS Providers. The API will support Java EE features and components within a web resource class.

InfoQ spoke to Pericas-Geertsen, who elaborated on server-sent events:

Server-sent-event (SSE) resources inject a special type called SseEventSink and produce text/event-stream. SSE clients use a SseEventSource to read events from a connection.

This mechanism uses long-lived connections and broadcasting, which provides improved performance over polling and resource-intensive, short-lived connections.

The following block illustrates the usage of SSE.

Server:

@GET
@Produces(MediaType.SERVER_SENT_EVENTS)
public void getMessageQueue(@Context Sse sse, @Context SseEventSink eventSink) {
    // Resource method is invoked when a client subscribes to an event stream.
    // That implies that sending events will most likely happen from different
    // context - thread / event handler / etc, so common implementation of the
    // resource method will store the eventSink instance and the application 
    // logic will retrieve it when an event should be emitted to the client.
    
    // sending events:
    eventSink.send(sse.newEvent("event1"));
}

Client:

WebTarget target = ClientBuilder.newClient().target("server-sent-events");

SseEventSource eventSource = SseEventSource.target(target).build();

// EventSource#register(Consumer<InboundSseEvent>)
// Registered event handler will print the received message.
eventSource.register(System.out::println);

// Subscribe to the event stream.
eventSource.open();

Pericas-Geertsen added:

  • JAX-RS 2.1 is fully backward compatible with previous releases.

  • The new features integrate very well with the existing JAX-RS concepts. For example, simply injecting a method call in a client invocation can switch processing from synchronous to reactive.

  • SSE relies on streaming HTTP-based connections so it is a natural extension to the existing APIs.

Since the API will use annotations and lambda expressions extensively, it will support applications developed in Java SE 8 or later.

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