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让我们展示如何使用Spring Cloud Stream来设计事件驱动的微服务。首先，Spring Cloud Stream首先有什么好处？因为Spring AMPQ提供了访问AMPQ工件所需的一切。如果您不熟悉Spring AMPQ，请查看此repo，其中包含许多有用的示例。那么为什么要使用Spring Cloud Stream ......？
Spring Cloud Stream概念
- Spring Cloud Stream通过Binder概念将使用过的消息代理与Spring Integration消息通道绑定在一起。支持RabbitMQ和Kafka。
- Spring Cloud Stream将基础架构配置从代码中分离为属性文件。这意味着即使您更改了底层代理，您的Spring Integration代码也将是相同的！
示例中的Spring Cloud Stream概念（RabbitMQ）
让我们有一个名为streamInput的交换，它有两个队列streamInput.cities和streamInput.persons。现在让我们将这两个队列插入两个消息通道citiesChannel和personsChannel来消费来自它的传入消息。使用Spring AMPQ，您需要创建SimpleMessageListenerContainer并在代码中连接基础结构。但这有很多样板代码。使用Spring Cloud Stream，您可以将AMPQ配置分离到属性文件：
spring.cloud.stream.bindings.citiesChannel.destination=streamInput
spring.cloud.stream.bindings.citiesChannel.group=cities
spring.cloud.stream.rabbit.bindings.citiesChannel.consumer.durableSubscription=true
spring.cloud.stream.rabbit.bindings.citiesChannel.consumer.bindingRoutingKey=cities
spring.cloud.stream.bindings.personsChannel.destination=streamInput
spring.cloud.stream.bindings.personsChannel.group=persons
spring.cloud.stream.rabbit.bindings.personsChannel.consumer.durableSubscription=true
spring.cloud.stream.rabbit.bindings.personsChannel.consumer.bindingRoutingKey=persons
配置详细信息
在类路径上使用RabbitMQ Binder,每个目标都映射到TopicExchange。在示例中，我创建了名为streamInput的TopicExchange， 并将其附加到两个消息通道citiesChannel和personsChannel。
spring.cloud.stream.bindings.citiesChannel.destination = streamInput
spring.cloud.stream.bindings.personsChannel.destination = streamInput
现在您需要了解RabbitMQ绑定器的灵感来自Kafka，队列的消费者被分组到消费者组中，其中只有一个消费者将获得消息。这是有道理的，因为您可以轻松扩展消费者。
因此，让我们创建两个队列streamInput.persons和streamInput.cities并将它们附加到streamInput TopicExchange和提到的消息通道
# This will create queue "streamInput.cities" connected to message channel citiesChannel where input messages will land.
spring.cloud.stream.bindings.citiesChannel.group=cities
# Durable subscription, of course.
spring.cloud.stream.rabbit.bindings.citiesChannel.consumer.durableSubscription=true
# AMPQ binding to exchange (previous spring.cloud.stream.bindings.<channel name>.destination settings).
# Only messages with routingKey = 'cities' will land here.
spring.cloud.stream.rabbit.bindings.citiesChannel.consumer.bindingRoutingKey=cities
spring.cloud.stream.bindings.personsChannel.group=persons
spring.cloud.stream.rabbit.bindings.personsChannel.consumer.durableSubscription=true
spring.cloud.stream.rabbit.bindings.personsChannel.consumer.bindingRoutingKey=persons
连接属性到Spring Integration
好的，到目前为止我创建了两个队列。StreamInput.cities绑定到citiesChannel。StreamInput.persons绑定到peopleChannel。
<destination>.<group>是Spring Cloud Stream约定的队列命名，现在让我们将它连接到Spring Integration：
package com.example.spring.cloud.configuration;
import org.springframework.cloud.stream.annotation.Input;
import org.springframework.messaging.SubscribableChannel;
/**
\* Created by tomask79 on 30.03.17.
*/
public interface SinkRabbitAPI {
String INPUT_CITIES = "citiesChannel";
String INPUT_PERSONS = "personsChannel";
@Input(SinkRabbitAPI.INPUT_CITIES)
SubscribableChannel citiesChannel();
@Input(SinkRabbitAPI.INPUT_PERSONS)
SubscribableChannel personsChannel();
}
Spring Boot启动时加载这个属性
package com.example.spring.cloud;
import com.example.spring.cloud.configuration.SinkRabbitAPI;
import com.example.spring.cloud.configuration.SourceRabbitAPI;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.scheduling.annotation.EnableScheduling;
@SpringBootApplication
@EnableBinding({SinkRabbitAPI.class})
public class StreamingApplication {
public static void main(String\[\] args) {
SpringApplication.run(StreamingApplication.class, args);
}
}
在此之后，我们可以创建消费者从绑定的消息通道中的队列接收消息：
import com.example.spring.cloud.configuration.SinkRabbitAPI;
import com.example.spring.cloud.configuration.SourceRabbitAPI;
import org.springframework.cloud.stream.annotation.StreamListener;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
/**
\* Created by tomask79 on 30.03.17.
*/
@Service
public class ProcessingAMPQEndpoint {
@StreamListener(SinkRabbitAPI.INPUT_CITIES)
public void processCity(final String city) {
System.out.println("Trying to process input city: "+city);
}
@StreamListener(SinkRabbitAPI.INPUT_PERSONS)
public void processPersons(final String person) {
System.out.println("Trying to process input person: "+person);
}
}
RabbitMQ绑定器和代理配置
Spring Cloud Stream如何知道在哪里寻找消息中间件？如果在类路径中找到RabbitMQ绑定器，则使用默认RabbitMQ主机（localhost）和端口（5672）连接到RabbitMQ服务器。如果您的消息中间件配置在不同端口，则需要配置属性：
spring:
cloud:
stream:
bindings:
...
binders:
rabbitbinder:
type: rabbit
environment:
spring:
rabbitmq:
host: rabbitmq
port: 5672
username: XXX
password: XXX
测试消息消费
- 安装并运行RabbitMQ代理
- rabbitmq.git
- mvn clean install
- java -jar target / streaming-0.0.1-SNAPSHOT.jar
- 现在使用路由键'cities'或'persons'在streamInput Exchange上发布消息...输出应该是：
Started StreamingApplication in 6.513 seconds (JVM running for 6.92)
Trying to process input city: sdjfjljksdflkjsdflkjsdfsfd
Trying to process input person: sdjfjljksdflkjsdflkjsdfsfd
使用Spring Cloud Stream重新传递消息
您通常希望在进入DLX交换之前再次尝试接收消息。首先，让我们配置Spring Cloud Stream尝试重新发送失败消息的次数：
spring.cloud.stream.bindings.personsChannel.consumer.maxAttempts = 6
这意味着如果从streamInput.persons队列接收的消息出错，那么Spring Cloud Stream将尝试重新发送六次。让我们试试，首先让我们修改接收端点以模拟接收崩溃：
@StreamListener(SinkRabbitAPI.INPUT_PERSONS)
public void processPersons(final String person) {
System.out.println("Trying to process input person: "+person);
throw new RuntimeException();
}
如果我现在尝试使用人员路由键将某些内容发布到streamInput交换中，那么这应该是输出：
Trying to process input person: sfsdfsdfsd
Trying to process input person: sfsdfsdfsd
Trying to process input person: sfsdfsdfsd
Trying to process input person: sfsdfsdfsd
Trying to process input person: sfsdfsdfsd
Trying to process input person: sfsdfsdfsd
Retry Policy Exhausted
at org.springframework.amqp.rabbit.retry.RejectAndDontRequeueRecoverer.recover
(RejectAndDontRequeueRecoverer.java:45) ~\[spring-rabbit-1.7.0.RELEASE.jar! /:na\]
at org.springframework.amqp.rabbit.config.StatelessRetryOperationsInterc
建议将Spring Cloud Stream 用于事件驱动的MicroServices，因为它可以节省时间，而且您不需要为Java中的AMPQ基础架构编写样板代码。
写在最后：
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