Spring Cloud Stream是一个用来为微服务应用构建消息驱动能力的框架，它为一些供应商的消息中间件产品提供了个性化的自动化配置实现，并且引入了发布-订阅、消费组以及分区这三个核心概念。通过使用Spring Cloud Stream，可以有效简化开发人员对消息中间件的使用复杂度，让系统开发人员可以有更多的精力关注于核心业务逻辑的处理。

在Spring Cloud Stream中，我们的微服务通过inputs或者outputs来与Spring Cloud Stream中的Binder进行交互，而这里的 Binder相当于微服务和消息中间件之间的一个粘合剂，这个Binder可以负责与消息中间件如RabbitMQ或者Kafka进行交互。拿RabbitMQ和Kafka来说，RabbitMQ支持优先级队列、延时队列、死信队列；Kafka支持消息分区...Spring Cloud Stream能够屏蔽掉这些消息中间件的具体实现功能细节，提供抽象的、统一的上层功能实现。这个时候对于开发者而言，我们只需要关注微服务和Spring Cloud Stream之间的通信方式，即消息要怎么样发送、怎么样订阅，做好这些工作之后，剩下的事情就交给Spring Cloud Stream来做，它会帮助我们完成和消息中间件之间的交互。

使用Binder，我们可以在程序运行时，动态修改消息的destination，具体到RabbitMQ中就是exchange，具体到Kafka中就是topic，这些我们都可以通过外部属性或者其它Spring Boot支持的配置方式（如application.properties或application.yml）来实现，甚至不需要改变一行代码（从下面的代码实现上来看，Spring Cloud Stream RabbitMQ和Spring Cloud Stream Kafka只有pom依赖和配置文件上的区别而已，除此之外的Java代码都是一样的）。

笔者使用的Java版本是jdk-8u201，IDE使用的是IntelliJ IDEA 2019.3 x64，Spring Boot的版本是2.1.9.RELEASE（RabbitMQ）、2.2.4.RELEASE（Kafka），Spring Cloud的版本是Greenwich.SR3（RabbitMQ）、Hoxton.SR1（Kafka）。

1 RabbitMQ

1.1 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.9.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.hys</groupId>
    <artifactId>spring-cloud-stream-rabbitmq</artifactId>
    <version>1.0-SNAPSHOT</version>
    <name>spring-cloud-stream-rabbitmq</name>
 
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR3</spring-cloud.version>
    </properties>
 
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-amqp</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-stream</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-stream-binder-rabbit</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.amqp</groupId>
            <artifactId>spring-rabbit-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-stream-test-support</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
 
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
 
</project>

1.2 application.properties

#connect
spring.rabbitmq.password=root
spring.rabbitmq.username=root
spring.rabbitmq.host=127.0.0.1
spring.rabbitmq.port=5672
#channel
spring.cloud.stream.bindings.mychannel-input.destination=mytopic
spring.cloud.stream.bindings.mychannel-output.destination=mytopic
#消息分组
spring.cloud.stream.bindings.mychannel-input.group=g1
spring.cloud.stream.bindings.mychannel-output.group=g1

1.3 自定义Channel

import org.springframework.cloud.stream.annotation.Input;
import org.springframework.cloud.stream.annotation.Output;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.SubscribableChannel;
 
public interface MyChannel {
 
    String INPUT = "mychannel-input";
    String OUTPUT = "mychannel-output";
 
    @Output(OUTPUT)
    MessageChannel output();
 
    @Input(INPUT)
    SubscribableChannel input();
}

1.4 生产者代码

import com.hys.springcloudstreamrabbitmq.service.MyChannel;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class HelloController {
 
    @Autowired
    private MyChannel myChannel;
 
    @GetMapping("test")
    public void hello() {
        myChannel.output().send(MessageBuilder.withPayload("hello stream!").build());
    }
}

1.5 消费者代码

import com.hys.springcloudstreamrabbitmq.service.MyChannel;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.StreamListener;
 
@EnableBinding(MyChannel.class)
public class MsgReceiver {
 
    @StreamListener(MyChannel.INPUT)
    public void receive(Object payload) {
        System.out.println("Received:" + payload);
    }
}

2 Kafka

2.1 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.hys</groupId>
    <artifactId>spring-cloud-stream-kafka</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-cloud-stream-kafka</name>
    <description>Demo project for Spring Boot</description>
 
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Hoxton.SR1</spring-cloud.version>
    </properties>
 
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-streams</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.kafka</groupId>
            <artifactId>spring-kafka</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-stream-binder-kafka</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.kafka</groupId>
            <artifactId>spring-kafka-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
 
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
 
</project>

2.2 application.properties

server.port=8080
spring.application.name=kafka-stream
spring.cloud.stream.kafka.binder.brokers=localhost:9092
spring.cloud.stream.bindings.mychannel-input.destination=mytopic
spring.cloud.stream.bindings.mychannel-output.destination=mytopic
spring.cloud.stream.bindings.mychannel-output.content-type=text/plain
#消息分组
spring.cloud.stream.bindings.mychannel-input.group=g1
spring.cloud.stream.bindings.mychannel-output.group=g1

2.3 自定义Channel

import org.springframework.cloud.stream.annotation.Input;
import org.springframework.cloud.stream.annotation.Output;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.SubscribableChannel;
 
public interface MyChannel {
 
    String INPUT = "mychannel-input";
    String OUTPUT = "mychannel-output";
 
    @Output(OUTPUT)
    MessageChannel output();
 
    @Input(INPUT)
    SubscribableChannel input();
}

2.4 生产者代码

import com.hys.kafka.service.MyChannel;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.support.MessageBuilder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class HelloController {
 
    @Autowired
    private MyChannel myChannel;
 
    @GetMapping("test")
    public void hello() {
        myChannel.output().send(MessageBuilder.withPayload("hello stream!").build());
    }
}

2.5 消费者代码

import com.hys.kafka.service.MyChannel;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.StreamListener;
 
@EnableBinding(MyChannel.class)
public class MsgReceiver {
 
    @StreamListener(MyChannel.INPUT)
    public void receive(Object payload) {
        System.out.println("Received:" + payload);
    }
}

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Spring Cloud消息驱动：Stream