Simple use of directexchange switches.

stay Fanout In the pattern , A message , Will be consumed by all subscribed queues . however , In some cases , We want different messages to be consumed by different queues . This is the time to use Direct Type of Exchange.

stay Direct Model Next ：

• The binding of queues to switches , It can't be arbitrary binding , But to To specify a RoutingKey（ route key）

• The sender of the message is towards Exchange When sending a message , You must also specify the RoutingKey.

• Exchange No longer give messages to each bound queue , It's based on the news Routing Key Judge , There's only a line of Routingkey With the news Routing key Exactly the same , To receive messages

  Specific code implementation

（1）： Among consumers

Declare queues and switches based on annotations

be based on @Bean It is troublesome to declare queues and switches in a way ,Spring Annotation based declarations are also provided .

stay consumer Of SpringRabbitListener Add two consumers , Both queues and switches are declared based on annotations ：

@RabbitListener(bindings = @QueueBinding(
    value = @Queue(name = "direct.queue1"),
    exchange = @Exchange(name = "itcast.direct", type = ExchangeTypes.DIRECT),
    key = {"red", "blue"}
))
public void listenDirectQueue1(String msg){
    System.out.println(" Consumers receive direct.queue1 The news of ：【" + msg + "】");
}

@RabbitListener(bindings = @QueueBinding(
    value = @Queue(name = "direct.queue2"),
    exchange = @Exchange(name = "itcast.direct", type = ExchangeTypes.DIRECT),
    key = {"red", "yellow"}
))
public void listenDirectQueue2(String msg){
    System.out.println(" Consumers receive direct.queue2 The news of ：【" + msg + "】");
}

（2：） Among producers

@Test
public void testSendDirectExchange() {
    //  Switch name 
    String exchangeName = "itcast.direct";
    //  news 
    String message = " Red Alert ！ Japan's indiscriminate discharge of nuclear waste water , Cause marine life to mutate , Surprise Godzilla ！";
    //  Send a message 
    rabbitTemplate.convertAndSend(exchangeName, "red", message);
}

Describe below Direct Switches and Fanout Switch differences ？

• Fanout The switch routes messages to each queue bound to it

• Direct Switch based on RoutingKey Determine which queue to route to

• If multiple queues have the same RoutingKey, Then with Fanout The function is similar to

be based on @RabbitListener Annotations declare what are common annotations for queues and switches ？

• @Queue

• @Exchange