By Josh Long

Spring Integration 4.1 was just released and it includes a lot of great new features! One of my favorites? Smart integration with the Spring 4 WebSocket support. Now you can compose a integration flow whose final destination is a WebSocket client. There is also support for acting as the client to a WebSocket service.

In order to compile it, you will need Java 8 (we make heavy use of lambdas here) and the following Maven dependencies:

• groupId:org.springframework.integration, artifactId:spring-integration-java-dsl, version: 1.0.0.RC1.
• groupId:org.springframework.integration, artifactId:spring-integration-websocket, version: 4.1.0.RELEASE.
• groupId:org.springframework.boot, artifactId:spring-boot-starter-websocket, version: 1.2.0.RC1.

In order to resolve those dependencies you will need the snapshot and milestone Maven repositories.

All clients listening on /names will receive whatever message is sent into the requestChannel channel. A Spring 4 MessageChannel is a named conduit - more or less analogous to a java.util.Queue<T>. This example uses the Spring Integration Java configuration DSL on top of the new Spring Integration 4.1 web socket support. Here’s the example:

package demo ;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.*;
import org.springframework.integration.channel.DirectChannel;
import org.springframework.integration.dsl.IntegrationFlow;
import org.springframework.integration.dsl.support.Function;
import org.springframework.integration.websocket.ServerWebSocketContainer;
import org.springframework.integration.websocket.outbound.WebSocketOutboundMessageHandler;
import org.springframework.messaging.*;
import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
import org.springframework.messaging.support.MessageBuilder;
import org.springframework.web.bind.annotation.*;

import java.util.concurrent.Executors;
import java.util.stream.Collectors;

/**
 * @author Artem Bilan
 * @author Josh Long
 */
@Configuration
@ComponentScan
@EnableAutoConfiguration
@RestController
public class Application {

    public static void main(String args[]) throws Throwable {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    ServerWebSocketContainer serverWebSocketContainer() {
        return new ServerWebSocketContainer("/names").withSockJs();
    }

    @Bean
    MessageHandler webSocketOutboundAdapter() {
        return new WebSocketOutboundMessageHandler(serverWebSocketContainer());
    }

    @Bean(name = "webSocketFlow.input")
    MessageChannel requestChannel() {
        return new DirectChannel();
    }

    @Bean
    IntegrationFlow webSocketFlow() {
        return f -> {
            Function<Message , Object> splitter = m -> serverWebSocketContainer()
                    .getSessions()
                    .keySet()
                    .stream()
                    .map(s -> MessageBuilder.fromMessage(m)
                            .setHeader(SimpMessageHeaderAccessor.SESSION_ID_HEADER, s)
                            .build())
                    .collect(Collectors.toList());
            f.split( Message.class, splitter)
                    .channel(c -> c.executor(Executors.newCachedThreadPool()))
                    .handle(webSocketOutboundAdapter());
        };
    }

    @RequestMapping("/hi/{name}")
    public void send(@PathVariable String name) {
        requestChannel().send(MessageBuilder.withPayload(name).build());
    }
}

The IntegrationFlow is simple. For each message that comes in, copy it and address it to each listening WebSocket session by adding a header having the SimpMessageHeaderAccessor.SESSION_ID_HEADER, then send it the outbound webSocketOutboundAdapter which will deliver it to each listening client. To see it work, open http://localhost:8080/ in one browser window, and then http://localhost:8080/hi/Spring in another. There is a simple client demonstrated in this techtip's code repository.

There is great documentation on how to use the web socket components in Spring Integration 4.1 documentation. There's a more inspiring example in the Spring Integration samples directory, too.