java-design-patterns/publish-subscribe/src/main/java/com/iluwatar/publish/subscribe/App.java

package com.iluwatar.publish.subscribe;

import org.apache.camel.CamelContext;
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.impl.DefaultCamelContext;

/**
 * 
 * When applications communicate with each other using a messaging system they first need to
 * establish a communication channel that will carry the data. Message Channel decouples Message
 * producers (publisher) and consumers (subscriber).
 * <p>
 * The sending application doesn't necessarily know what particular applications will end up
 * retrieving it, but it can be assured that the application that retrieves the information is
 * interested in that information. This is because the messaging system has different Message
 * Channels for different types of information the applications want to communicate. When an
 * application sends information, it doesn't randomly add the information to any channel available;
 * it adds it to a channel whose specific purpose is to communicate that sort of information.
 * Likewise, an application that wants to receive particular information doesn't pull info off some
 * random channel; it selects what channel to get information from based on what type of information
 * it wants.
 * <p>
 * In this example we use Apache Camel to establish different Message Channels. The first one reads
 * from standard input and delivers messages to Direct endpoints (Publish; Broadcast). The other
 * Message Channels are established from the Direct component to different Endpoints (Subscriber).
 * No actual messages are sent, only the established routes are printed to standard output.
 * 
 */
public class App {

  /**
   * Program entry point
   * 
   * @param args
   *          command line args
   * @throws Exception
   */
  public static void main(String[] args) throws Exception {
    CamelContext context = new DefaultCamelContext();

    context.addRoutes(new RouteBuilder() {

      @Override
      public void configure() throws Exception {
        from("stream:in").multicast().to("direct:greetings1", "direct:greetings2",
            "direct:greetings3");
      }
    });

    context.start();
    context.getRoutes().stream().forEach((r) -> System.out.println(r));
    context.stop();
  }
}