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目录

• 生产端 Confirm 消息确认机制
  • Confirm 确认机制流程图
  • 如何实现Confirm确认消息?
  • 注意事项
• Return 消息机制
  • Return 消息机制流程图
  • Return 消息示例
• 消费端 Ack 和 Nack 机制
  • 参考 api
  • 如何设置手动 Ack 、Nack 以及重回队列

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生产端 Confirm 消息确认机制

消息的确认，是指生产者投递消息后，如果 Broker 收到消息，则会给我们生产者一个应答。生产者进行接收应答，用来确定这条消息是否正常的发送到 Broker ，这种方式也是消息的可靠性投递的核心保障!

Confirm 确认机制流程图

如何实现Confirm确认消息?

• 第一步:在 channel 上开启确认模式: channel.confirmSelect()
• 第二步:在 channel 上添加监听: channel.addConfirmListener(ConfirmListener listener);, 监听成功和失败的返回结果，根据具体的结果对消息进行重新发送、或记录日志等后续处理!

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.ConfirmListener;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;import java.io.IOException;public class ConfirmProducer {public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");Connection connection = factory.newConnection();Channel channel = connection.createChannel();String exchangeName = "test_confirm_exchange";String routingKey = "item.update";//指定消息的投递模式：confirm 确认模式channel.confirmSelect();//发送final long start = System.currentTimeMillis();for (int i = 0; i < 5 ; i++) {String msg = "this is confirm msg ";channel.basicPublish(exchangeName, routingKey, null, msg.getBytes());System.out.println("Send message : " + msg);}//添加一个确认监听， 这里就不关闭连接了，为了能保证能收到监听消息channel.addConfirmListener(new ConfirmListener() {/*** 返回成功的回调函数*/public void handleAck(long deliveryTag, boolean multiple) throws IOException {System.out.println("succuss ack");System.out.println(multiple);System.out.println("耗时：" + (System.currentTimeMillis() - start) + "ms");}/*** 返回失败的回调函数*/public void handleNack(long deliveryTag, boolean multiple) throws IOException {System.out.printf("defeat ack");System.out.println("耗时：" + (System.currentTimeMillis() - start) + "ms");}});}
}

import com.rabbitmq.client.*;
import java.io.IOException;public class ConfirmConsumer {public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");factory.setAutomaticRecoveryEnabled(true);factory.setNetworkRecoveryInterval(3000);Connection connection = factory.newConnection();Channel channel = connection.createChannel();String exchangeName = "test_confirm_exchange";String queueName = "test_confirm_queue";String routingKey = "item.#";channel.exchangeDeclare(exchangeName, "topic", true, false, null);channel.queueDeclare(queueName, false, false, false, null);//一般不用代码绑定，在管理界面手动绑定channel.queueBind(queueName, exchangeName, routingKey);//创建消费者并接收消息Consumer consumer = new DefaultConsumer(channel) {@Overridepublic void handleDelivery(String consumerTag, Envelope envelope,AMQP.BasicProperties properties, byte[] body)throws IOException {String message = new String(body, "UTF-8");System.out.println(" [x] Received '" + message + "'");}};//设置 Channel 消费者绑定队列channel.basicConsume(queueName, true, consumer);}
}

我们此处只关注生产端输出消息

Send message : this is confirm msg 
Send message : this is confirm msg 
Send message : this is confirm msg 
Send message : this is confirm msg 
Send message : this is confirm msg 
succuss ack
true
耗时：3ms
succuss ack
true
耗时：4ms

注意事项

• 我们采用的是异步 confirm 模式：提供一个回调方法，服务端 confirm 了一条或者多条消息后 Client 端会回调这个方法。除此之外还有单条同步 confirm 模式、批量同步 confirm 模式，由于现实场景中很少使用我们在此不做介绍，如有兴趣直接参考官方文档。

• 我们运行生产端会发现每次运行结果都不一样,会有多种情况出现，因为 Broker 会进行优化，有时会批量一次性 confirm ，有时会分开几条 confirm。

  succuss acktrue耗时：3mssuccuss ackfalse耗时：4ms或者succuss acktrue耗时：3ms

Return 消息机制

• Return Listener 用于处理一-些不可路 由的消息!
• 消息生产者，通过指定一个 Exchange 和 Routingkey，把消息送达到某一个队列中去，然后我们的消费者监听队列，进行消费处理操作!

• 但是在某些情况下，如果我们在发送消息的时候，当前的 exchange 不存在或者指定的路由 key 路由不到，这个时候如果我们需要监听这种不可达的消息，就要使用 Return Listener !

• 在基础API中有一个关键的配置项:Mandatory：如果为 true，则监听器会接收到路由不可达的消息，然后进行后续处理，如果为 false，那么 broker 端自动删除该消息!

Return 消息机制流程图

Return 消息示例

• 首先我们需要发送三条消息，并且故意将第 0 条消息的 routing Key设置为错误的，让他无法正常路由到消费端。

• mandatory 设置为 true 路由不可达的消息会被监听到，不会被自动删除.即channel.basicPublish(exchangeName, errRoutingKey, true,null, msg.getBytes());

• 最后添加监听即可监听到不可路由到消费端的消息channel.addReturnListener(ReturnListener r))

import com.rabbitmq.client.*;
import java.io.IOException;public class ReturnListeningProducer {public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");Connection connection = factory.newConnection();Channel channel = connection.createChannel();String exchangeName = "test_return_exchange";String routingKey = "item.update";String errRoutingKey = "error.update";//指定消息的投递模式：confirm 确认模式channel.confirmSelect();//发送for (int i = 0; i < 3 ; i++) {String msg = "this is return——listening msg ";//@param mandatory 设置为 true 路由不可达的消息会被监听到，不会被自动删除if (i == 0) {channel.basicPublish(exchangeName, errRoutingKey, true,null, msg.getBytes());} else {channel.basicPublish(exchangeName, routingKey, true, null, msg.getBytes());}System.out.println("Send message : " + msg);}//添加一个确认监听， 这里就不关闭连接了，为了能保证能收到监听消息channel.addConfirmListener(new ConfirmListener() {/*** 返回成功的回调函数*/public void handleAck(long deliveryTag, boolean multiple) throws IOException {System.out.println("succuss ack");}/*** 返回失败的回调函数*/public void handleNack(long deliveryTag, boolean multiple) throws IOException {System.out.printf("defeat ack");}});//添加一个 return 监听channel.addReturnListener(new ReturnListener() {public void handleReturn(int replyCode, String replyText, String exchange, String routingKey, AMQP.BasicProperties properties, byte[] body) throws IOException {System.out.println("return relyCode: " + replyCode);System.out.println("return replyText: " + replyText);System.out.println("return exchange: " + exchange);System.out.println("return routingKey: " + routingKey);System.out.println("return properties: " + properties);System.out.println("return body: " + new String(body));}});}
}

import com.rabbitmq.client.*;
import java.io.IOException;public class ReturnListeningConsumer {public static void main(String[] args) throws Exception {//1. 创建一个 ConnectionFactory 并进行设置ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");factory.setAutomaticRecoveryEnabled(true);factory.setNetworkRecoveryInterval(3000);//2. 通过连接工厂来创建连接Connection connection = factory.newConnection();//3. 通过 Connection 来创建 ChannelChannel channel = connection.createChannel();//4. 声明String exchangeName = "test_return_exchange";String queueName = "test_return_queue";String routingKey = "item.#";channel.exchangeDeclare(exchangeName, "topic", true, false, null);channel.queueDeclare(queueName, false, false, false, null);//一般不用代码绑定，在管理界面手动绑定channel.queueBind(queueName, exchangeName, routingKey);//5. 创建消费者并接收消息Consumer consumer = new DefaultConsumer(channel) {@Overridepublic void handleDelivery(String consumerTag, Envelope envelope,AMQP.BasicProperties properties, byte[] body)throws IOException {String message = new String(body, "UTF-8");System.out.println(" [x] Received '" + message + "'");}};//6. 设置 Channel 消费者绑定队列channel.basicConsume(queueName, true, consumer);}
}

我们只关注生产端结果，消费端只收到两条消息。

Send message : this is return——listening msg 
Send message : this is return——listening msg 
Send message : this is return——listening msg 
return relyCode: 312
return replyText: NO_ROUTE
return exchange: test_return_exchange
return routingKey: error.update
return properties: #contentHeader<basic>(content-type=null, content-encoding=null, headers=null, delivery-mode=null, priority=null, correlation-id=null, reply-to=null, expiration=null, message-id=null, timestamp=null, type=null, user-id=null, app-id=null, cluster-id=null)
return body: this is return——listening msg 
succuss ack
succuss ack
succuss ack

消费端 Ack 和 Nack 机制

消费端进行消费的时候，如果由于业务异常我们可以进行日志的记录，然后进行补偿!如果由于服务器宕机等严重问题，那我们就需要手工进行ACK保障消费端消费成功!消费端重回队列是为了对没有处理成功的消息，把消息重新会递给Broker!一般我们在实际应用中，都会关闭重回队列，也就是设置为False。

参考 api

void basicNack(long deliveryTag, boolean multiple, boolean requeue) throws IOException;

void basicAck(long deliveryTag, boolean multiple) throws IOException;

如何设置手动 Ack 、Nack 以及重回队列

• 首先我们发送五条消息，将每条消息对应的循环下标 i 放入消息的 properties 中作为标记，以便于我们在后面的回调方法中识别。

• 其次， 我们将消费端的 ·channel.basicConsume(queueName, false, consumer); 中的 autoAck属性设置为 false，如果设置为true的话 将会正常输出五条消息。

• 我们通过 Thread.sleep(2000)来延时一秒，用以看清结果。我们获取到properties中的num之后，通过channel.basicNack(envelope.getDeliveryTag(), false, true);将 num为0的消息设置为 nack，即消费失败，并且将 requeue属性设置为true，即消费失败的消息重回队列末端。

import com.rabbitmq.client.*;
import java.util.HashMap;
import java.util.Map;public class AckAndNackProducer {public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");Connection connection = factory.newConnection();Channel channel = connection.createChannel();String exchangeName = "test_ack_exchange";String routingKey = "item.update";String msg = "this is ack msg";for (int i = 0; i < 5; i++) {Map<String, Object> headers = new HashMap<String, Object>();headers.put("num" ,i);AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().deliveryMode(2).headers(headers).build();String tem = msg + ":" + i;channel.basicPublish(exchangeName, routingKey, true, properties, tem.getBytes());System.out.println("Send message : " + msg);}channel.close();connection.close();}
}

import com.rabbitmq.client.*;
import java.io.IOException;public class AckAndNackConsumer {public static void main(String[] args) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");factory.setVirtualHost("/");factory.setUsername("guest");factory.setPassword("guest");factory.setAutomaticRecoveryEnabled(true);factory.setNetworkRecoveryInterval(3000);Connection connection = factory.newConnection();final Channel channel = connection.createChannel();String exchangeName = "test_ack_exchange";String queueName = "test_ack_queue";String routingKey = "item.#";channel.exchangeDeclare(exchangeName, "topic", true, false, null);channel.queueDeclare(queueName, false, false, false, null);//一般不用代码绑定，在管理界面手动绑定channel.queueBind(queueName, exchangeName, routingKey);Consumer consumer = new DefaultConsumer(channel) {@Overridepublic void handleDelivery(String consumerTag, Envelope envelope,AMQP.BasicProperties properties, byte[] body)throws IOException {String message = new String(body, "UTF-8");System.out.println(" [x] Received '" + message + "'");try {Thread.sleep(2000);} catch (InterruptedException e) {e.printStackTrace();}if ((Integer) properties.getHeaders().get("num") == 0) {channel.basicNack(envelope.getDeliveryTag(), false, true);} else {channel.basicAck(envelope.getDeliveryTag(), false);}}};//6. 设置 Channel 消费者绑定队列channel.basicConsume(queueName, false, consumer);}
}

我们此处只关心消费端输出，可以看到第 0 条消费失败重新回到队列尾部消费。

 [x] Received 'this is ack msg:1'[x] Received 'this is ack msg:2'[x] Received 'this is ack msg:3'[x] Received 'this is ack msg:4'[x] Received 'this is ack msg:0'[x] Received 'this is ack msg:0'[x] Received 'this is ack msg:0'[x] Received 'this is ack msg:0'[x] Received 'this is ack msg:0'