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Headers 类型的Exchanges是不处理路由键的，而是根据发送的消息内容中的headers属性进行匹配。在绑定Queue与Exchange时指定一组键值对；当消息发送到RabbitMQ时会取到该消息的headers与Exchange绑定时指定的键值对进行匹配；如果完全匹配则消息会路由到该队列，否则不会路由到该队列。headers属性是一个键值对，可以是Hashtable，键值对的值可以是任何类型。而fanout，direct，topic 的路由键都需要要字符串形式的。

匹配规则x-match有下列两种类型：x-match = all   ：表示所有的键值对都匹配才能接受到消息

x-match = any ：表示只要有键值对匹配就能接受到消息

不过headers比较少用到，下面是headers的官方说明文档：

A headers exchange is designed to for routing on multiple attributes that are more easily expressed as message headers than a routing key. Headers exchanges ignore the routing key attribute. Instead, the attributes used for routing are taken from the headers attribute. A message is considered matching if the value of the header equals the value specified upon binding.

It is possible to bind a queue to a headers exchange using more than one header for matching. In this case, the broker needs one more piece of information from the application developer, namely, should it consider messages with any of the headers matching, or all of them? This is what the "x-match" binding argument is for. When the "x-match" argument is set to "any", just one matching header value is sufficient. Alternatively, setting "x-match" to "all" mandates that all the values must match.

Headers exchanges can be looked upon as "direct exchanges on steroids". Because they route based on header values, they can be used as direct exchanges where the routing key does not have to be a string; it could be an integer or a hash (dictionary) for example.

下面贴出headers的事例代码！！

Consumer：package headers;

import java.io.IOException;

import java.util.Hashtable;

import java.util.Map;

import java.util.concurrent.TimeoutException;

import com.rabbitmq.client.AMQP;

import com.rabbitmq.client.Channel;

import com.rabbitmq.client.Connection;

import com.rabbitmq.client.ConnectionFactory;

import com.rabbitmq.client.Consumer;

import com.rabbitmq.client.DefaultConsumer;

import com.rabbitmq.client.Envelope;

public class HeadersConsumer {

private static final String EXCHANGE_NAME = "exchange_headers";

private static final String QUEUE_NAME = "headers_test_queue";

public static void main(String[] argv) throws IOException, TimeoutException  {

new ExchangeHeaders();

}

static class ExchangeHeaders{

public  ExchangeHeaders() throws IOException, TimeoutException {

ConnectionFactory factory = new ConnectionFactory();

//rabbitmq监听IP

factory.setHost("192.168.249.128");

//rabbitmq监听默认端口

factory.setPort(5672);

//设置访问的用户

factory.setUsername("test");

factory.setPassword("test");

Connection connection = factory.newConnection();

Channel channel = connection.createChannel();

//声明路由名字和类型

channel.exchangeDeclare(EXCHANGE_NAME, "headers", false, true, null);

//创建队列

channel.queueDeclare(QUEUE_NAME, false, false, true, null);

//设置消息头键值对信息

Map headers = new Hashtable();

//这里x-match有两种类型

//all:表示所有的键值对都匹配才能接受到消息

//any:表示只要有键值对匹配就能接受到消息

headers.put("x-match", "any");

headers.put("name", "jack");

headers.put("age" , 31);

//把队列绑定到路由上并指定headers

channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "", headers);

System.out.println(" Waiting for msg....");

Consumer consumer = new DefaultConsumer(channel) {

@Override

public void handleDelivery(String consumerTag, Envelope envelope,

AMQP.BasicProperties properties, byte[] body) throws IOException {

String message = new String(body, "UTF-8");

System.out.println("Received msg is '" + message + "'");

}

};

channel.basicConsume(QUEUE_NAME, true, consumer);

}

}

}

Producer：package headers;

import java.io.IOException;

import java.util.Hashtable;

import java.util.Map;

import java.util.concurrent.TimeoutException;

import com.rabbitmq.client.AMQP.BasicProperties.Builder;

import com.rabbitmq.client.Channel;

import com.rabbitmq.client.Connection;

import com.rabbitmq.client.ConnectionFactory;

public class HeadersProducer {

private static final String EXCHANGE_NAME = "exchange_headers";

public static void main(String[] argv) throws Exception{

new ExchangeHeaders("exchanges type headers test msg~");

}

static class ExchangeHeaders{

public ExchangeHeaders(String message) throws IOException, TimeoutException{

ConnectionFactory factory = new ConnectionFactory();

//rabbitmq监听IP

factory.setHost("192.168.249.128");

//rabbitmq监听默认端口

factory.setPort(5672);

//设置访问的用户

factory.setUsername("test");

factory.setPassword("test");

Connection connection = factory.newConnection();

Channel channel = connection.createChannel();

//声明路由名字和类型

channel.exchangeDeclare(EXCHANGE_NAME, "headers", false, true, null);

//设置消息头键值对信息

Map headers = new Hashtable();

headers.put("name", "jack");

headers.put("age", 30);

Builder builder = new Builder();

builder.headers(headers);

channel.basicPublish(EXCHANGE_NAME, "", builder.build(), message.getBytes());

System.out.println("Sent msg is '" + message + "'");

channel.close();

connection.close();

}

}

}

运行结果：

注意如果将Consumer中的headers.put("x-match", "any");改成headers.put("x-match", "all"); 则不会接受到消息！！

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