RabbitMQ的消费者处理消息失败后之重试3次，重试3次仍然失败发送到死信队列。
1、为什么要重试？
如果消费者处理消息失败后不重试，然后发送应答给rabbitmq，rabbitmq就会将队列中的消息删除，从而造成消息的丢失。所以我们要在消费者处理消息失败的时候，重试一定的次数。比如重试3次，如果重试3次之后还是失败，则把这条消息发送到死信队列。
所以我们现在要实现消息的重试，实现效果为：
首先，将消息携带routtingkey的消息发送到正常转发器exchange@normal，exchange@normal将消息发送到正常队列queue@normal，queue@normal得到消息后进行处理，如果处理成功，则给rabbitmq发送应答。如果消息处理失败，判断消息失败的次数：如果失败次数小于3次，则将消息发送到重试转发器exchange@retry，exchange@retry得到消息后，发送到重试队列queue@retry，queue@retry10s后，将该条消息再次发送到正常转发器exchange@normal进行正常的消费；如果失败次数超过3次，则将消息发送到失败转发器exchange@filed，exchange@filed将失败了的消息发送给失败队列queue@filed，然后可以根据业务需求处理失败了的数据。比如保存到失败文件或者数据库等，也可以人工处理后，重新发送给exchange@normal。
思路图如下：
2、重试实现的思路
生产者端发送消息：
1）、声明三个转发器
//正常的转发器
private static String NORMAL_EXCHANGE = "exchange@normal";
//重试转发器
private static String RETRY_EXCHANGE = "exchange@retry";
//失败转发器
private static String FILED_EXCHANGE = "exchange@filed";
......
//声明正常的转发器
channel.exchangeDeclare(NORMAL_EXCHANGE,"topic");
//声明重试的转发器
channel.exchangeDeclare(RETRY_EXCHANGE,"topic");
//声明失败的转发器
channel.exchangeDeclare(FILED_EXCHANGE,"topic");2)、发送消息到正常的队列
//发送5条消息到正常的转发器，路由密匙为normal
for(int i=0;i<5;i++){
String message = "retry..."+i;
channel.basicPublish(NORMAL_EXCHANGE,"normal",
MessageProperties.PERSISTENT_BASIC,message.getBytes());
}消费者端接受、处理消息：
1）、定义并声明转发器和队列，需要注意的是queue@normal和queue@filed两个队列就是普通的队列。queue@retry队列需要设置两个参数：x-dead-letter-exchange、x-message-ttl。这两个参数按照我自己的理解是x-dead-letter-exchange指定重试时将消息重发给哪一个转发器、x-message-ttl消息到达重试队列后，多长时间后重发。
//转发器
private static String NORMAL_EXCHANGE = "exchange@normal";
private static String RETRY_EXCHANGE = "exchange@retry";
private static String FILED_EXCHANGE = "exchange@filed";
//队列
private static String NORMAL_QUEUE = "queue@normal";
private static String RETRY_QUEUE = "queue@retry";
private static String FILED_QUEUE = "queue@filed";
......
//声明正常队列
channel.queueDeclare(NORMAL_QUEUE,true,false,false,null);
//声明重试队列,重试队列比较特殊，需要设置两个参数
Map arg = new HashMap();
//参数1：将消息发送到哪一个转发器
arg.put("x-dead-letter-exchange",NORMAL_EXCHANGE);
//参数2：多长时间后重发
arg.put("x-message-ttl",10000);
channel.queueDeclare(RETRY_QUEUE,true,false,false,arg);
//声明失败队列
channel.queueDeclare(FILED_QUEUE,true,false,false,null); 2）、将队列绑定转发器和路由密匙
//将队列绑定转发器和路由密匙
channel.queueBind(NORMAL_QUEUE,NORMAL_EXCHANGE,"normal");
channel.queueBind(RETRY_QUEUE,RETRY_EXCHANGE,"normal");
channel.queueBind(FILED_QUEUE,FILED_EXCHANGE,"normal");3）、定义consumer，消费消息。因为消息设置的是自动应答，所以不需要手动应答。如果你设置了手动应答，则在消息消费成功或者失败后都要应答。
Consumer consumer = new DefaultConsumer(channel){
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
//此处处理消息
try{
String message = new String(body,"utf-8");
System.out.println("消费者接受到的消息："+message);
//模拟处理消息产生异常
int i = 1/0;
}catch(Exception e){
try{
//延迟5s
Thread.sleep(5000);
//判断失败次数
long retryCount = getRetryCount(properties);
if(retryCount>=3){
//如果失败超过三次，则发送到失败队列
channel.basicPublish(FILED_EXCHANGE,envelope.getRoutingKey(),MessageProperties.PERSISTENT_BASIC,body);
System.out.println("消息失败了...");
}else{
//发送到重试队列,10s后重试
channel.basicPublish(RETRY_EXCHANGE,envelope.getRoutingKey(),properties,body);
System.out.println("消息重试中...");
}
}catch (Exception e1){
e.printStackTrace();
}
}
}
};
//消费消息
channel.basicConsume(NORMAL_QUEUE,true,consumer);判断消息失败次数的方法如下：
public long getRetryCount(AMQP.BasicProperties properties){
long retryCount = 0L;
Map header = properties.getHeaders();
if(header != null && header.containsKey("x-death")){
List> deaths = (List>)header.get("x-death");
if(deaths.size()>0){
Map death = deaths.get(0);
retryCount = (Long)death.get("count");
}
}
return retryCount;
} 重试的完整代码如下：
1）、生产者
@Component
public class RetryPublisher {
private static String NORMAL_EXCHANGE = "exchange@normal";
private static String RETRY_EXCHANGE = "exchange@retry";
private static String FILED_EXCHANGE = "exchange@filed";
public void send(){
Connection connection = ConnectionUtil.getInstance();
Channel channel = null;
try{
channel = connection.createChannel();
//声明正常的转发器
channel.exchangeDeclare(NORMAL_EXCHANGE,"topic");
//声明重试的转发器
channel.exchangeDeclare(RETRY_EXCHANGE,"topic");
//声明失败的转发器
channel.exchangeDeclare(FILED_EXCHANGE,"topic");
//发送5条消息到正常的转发器，路由密匙为normal
for(int i=0;i<5;i++){
String message = "retry..."+i;
channel.basicPublish(NORMAL_EXCHANGE,"normal", MessageProperties.PERSISTENT_BASIC,message.getBytes());
}
}catch (Exception e){
}
}
}2）、消费者方法和判断消息失败次数的方法
@Component
public class RetryReceiver {
//转发器
private static String NORMAL_EXCHANGE = "exchange@normal";
private static String RETRY_EXCHANGE = "exchange@retry";
private static String FILED_EXCHANGE = "exchange@filed";
//队列
private static String NORMAL_QUEUE = "queue@normal";
private static String RETRY_QUEUE = "queue@retry";
private static String FILED_QUEUE = "queue@filed";
public void receiver(){
Connection connection = ConnectionUtil.getInstance();
final Channel channel;
try{
channel = connection.createChannel();
//声明正常队列
channel.queueDeclare(NORMAL_QUEUE,true,false,false,null);
//声明重试队列,重试队列比较特殊，需要设置两个参数
Map arg = new HashMap();
//参数1：将消息发送到哪一个转发器
arg.put("x-dead-letter-exchange",NORMAL_EXCHANGE);
//参数2：多长时间后发送
arg.put("x-message-ttl",10000);
channel.queueDeclare(RETRY_QUEUE,true,false,false,arg);
//声明失败队列
channel.queueDeclare(FILED_QUEUE,true,false,false,null);
//将队列绑定转发器和路由密匙
channel.queueBind(NORMAL_QUEUE,NORMAL_EXCHANGE,"normal");
channel.queueBind(RETRY_QUEUE,RETRY_EXCHANGE,"normal");
channel.queueBind(FILED_QUEUE,FILED_EXCHANGE,"normal");
Consumer consumer = new DefaultConsumer(channel){
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
//此处处理消息
try{
String message = new String(body,"utf-8");
System.out.println("消费者接受到的消息："+message);
//模拟处理消息是产生异常
int i = 1/0;
}catch(Exception e){
try{
//延迟5s
Thread.sleep(5000);
//判断失败次数
long retryCount = getRetryCount(properties);
if(retryCount>=3){
//如果失败超过三次，则发送到失败队列
channel.basicPublish(FILED_EXCHANGE,envelope.getRoutingKey(),MessageProperties.PERSISTENT_BASIC,body);
System.out.println("消息失败了...");
}else{
//发送到重试队列,10s后重试
channel.basicPublish(RETRY_EXCHANGE,envelope.getRoutingKey(),properties,body);
System.out.println("消息重试中...");
}
}catch (Exception e1){
e.printStackTrace();
}
}
}
};
//消费消息
channel.basicConsume(NORMAL_QUEUE,true,consumer);
}catch (Exception e){
e.printStackTrace();
}
}
/**
* 获取消息失败次数
* @param properties
* @return
*/
public long getRetryCount(AMQP.BasicProperties properties){
long retryCount = 0L;
Map header = properties.getHeaders();
if(header != null && header.containsKey("x-death")){
List> deaths = (List>)header.get("x-death");
if(deaths.size()>0){
Map death = deaths.get(0);
retryCount = (Long)death.get("count");
}
}
return retryCount;
}
}
3）、测试Controlelr
@Controller
public class RetryController {
@Autowired
private RetryPublisher publisher;
@Autowired
private RetryReceiver receiver;
@RequestMapping("/retrySend")
@ResponseBody
public void send(){
publisher.send();
}
@RequestMapping("/retryReceive")
@ResponseBody
public void receive(){
receiver.receiver();
}
}本文的思路图来自博主：https://www.cnblogs.com/itrena/p/9044097.html