在使用RabbitMQ向Broker发送消息时,有一个mandatory参数.默认情况下,该参数为false.该参数与回调ReturnListener有关.
回调ReturnListener需要满足以下条件:

• 发送消息到达Exchange,但是Exchange没有与其他Queue绑定
• mandatory设置为true.
  如果上面两个条件任何一个条件没有满足是不会触发ReturnListener回调的.

例子一:

public class MandatoryDemo {
    public static void main(String[] args) throws IOException, TimeoutException {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("127.0.0.1");
        factory.setUsername("root");
        factory.setPassword("root");
        factory.setPort(5672);
        factory.setVirtualHost("/order");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();
        channel.confirmSelect();
        
        //创建exchange
        channel.exchangeDeclare("exchange_1",BuiltinExchangeType.FANOUT,true);

        channel.addReturnListener(new ReturnListener() {
            @Override
            public void handleReturn(int replyCode, String replyText, String exchange, String routingKey, AMQP.BasicProperties properties, byte[] body) throws IOException {
                System.out.println("replyCode = " + replyCode);
                System.out.println("replyText = " + replyText);
                System.out.println("exchange = " + exchange);
                System.out.println("properties = " + properties);
                System.out.println("body = " + new String(body));
            }
        });

        channel.addShutdownListener(new ShutdownListener() {
            @Override
            public void shutdownCompleted(ShutdownSignalException cause) {
                System.out.println("cause = " + cause);
            }
        });
        //设置mandatory为true
        channel.basicPublish("exchange_1","",true,MessageProperties.PERSISTENT_TEXT_PLAIN,"test_message".getBytes());

    }
}

上面代码有两个关键的地方:

• 创建exchange
• 发送消息时,mandatory设置为true

如果exchange没有创建时,则会报一下错误,会触发ShutdownListener回调:

cause = com.rabbitmq.client.ShutdownSignalException: channel error; protocol method: #method<channel.close>(reply-code=404, reply-text=NOT_FOUND - no exchange 'exchange_1' in vhost '/order', class-id=60, method-id=40)

如果mandatory没有设置为true,运行结果是控制台不会输出任何信息,即不会触发ReturnListener回调