SpringCloud之Spring Cloud Stream：消息驱动

Spring Cloud Stream 是一个构建消息驱动微服务的框架，该框架在Spring Boot的基础上整合了Spring Integrationg来连接消息代理中间件(RabbitMQ, Kafka等)，提供了个性化的自动化配置实现，并引入了发布-订阅、消费组、分区这三个核心概念。
应用程序通过input通道或者output通道来与Spring Cloud Stream中binder（绑定器）交互，通过配置来binding. 而Spring Cloud Stream的binder负责与中间件交互。

开发工具：IntelliJ IDEA 2019.2.3

一、服务器端

1、创建项目

IDEA中创建一个新的SpringBoot项目，名称为“spring-server”，SpringBoot版本选择2.1.10，在选择Dependencies(依赖)的界面勾选Spring Cloud Discovery -> Eureka Server。
pom.xml完整内容如下：

<?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>2.1.10.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>spring-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-server</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR4</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-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、修改配置application.yml

修改端口号为8761；取消将自己信息注册到Eureka服务器，不从Eureka服务器抓取注册信息。

server:
  port: 8761
eureka:
  client:
    register-with-eureka: false
    fetch-registry: false

3、修改启动类代码

增加注解@EnableEurekaServer

package com.example.springserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@SpringBootApplication
@EnableEurekaServer
public class SpringServerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringServerApplication.class, args);
    }

}

二、消息生产者

1、创建项目
IDEA中创建一个新的SpringBoot项目，名称为“spring-producer”，SpringBoot版本选择2.1.10，在选择Dependencies(依赖)的界面勾选Web -> Spring Web，Spring Cloud Discovery -> Eureka Discovery Client。
打开pom.xml，添加依赖spring-cloud-starter-stream-rabbit，会自动引入spring-cloud-stream和spring-cloud-stream-binder。
pom.xml完整内容如下：

<?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>2.1.10.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>spring-producer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-producer</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR4</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-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>

2、修改配置application.yml

pom.xml使用RabbitMQ，默认情况下，连接本地的5672端口。下面这段rabbitmq也可省略。

server:
  port: 8081
spring:
  application:
    name: spring-producer
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
rabbitmq:
  host: localhost
  post: 5672
  username: guest
  password: guest

3、编写发送服务

方法sendOrder使用@Output("myInput")注解表示创建myInput的消息通道。调用该方法后，会向myInput通道投递消息。
如果不使用参数myInput，则使用方法名作为通道名称。

package com.example.springproducer;

import org.springframework.cloud.stream.annotation.Output;
import org.springframework.messaging.SubscribableChannel;

public interface SendService {
    @Output("myInput")
    SubscribableChannel sendOrder();
}

4、修改启动类代码

加入注解@EnableBinding以开启Spring容器的绑定功能，以SendService.class为参数，Spring容器启动时，会自动绑定SendService接口中定义的通道。

package com.example.springproducer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.stream.annotation.EnableBinding;

@SpringBootApplication
@EnableEurekaClient
@EnableBinding(SendService.class)
public class SpringProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringProducerApplication.class, args);
    }

}

5、添加一个控制器类

调用SendService的发送方法，往服务器发送消息。

package com.example.springproducer;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.Message;
import org.springframework.messaging.support.MessageBuilder;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ProducerController {

    @Autowired
    SendService sendService;

    @RequestMapping(value="/send",method= RequestMethod.GET)
    public String sendRequest(){
        //创建消息
        Message msg = MessageBuilder.withPayload("hello world".getBytes()).build();
        //发送消息
        sendService.sendOrder().send(msg);
        return "SUCCESS";
    }
}

三、消息消费者

1、创建项目

IDEA中创建一个新的SpringBoot项目，名称为“spring-consumer”，SpringBoot版本选择2.1.10，在选择Dependencies(依赖)的界面勾选Web -> Spring Web，Spring Cloud Discovery -> Eureka Discovery Client。
打开pom.xml，添加依赖spring-cloud-starter-stream-rabbit

<?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>2.1.10.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>spring-consumer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-consumer</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR4</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-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、修改配置application.yml

server:
  port: 8080
spring:
  application:
    name: spring-consumer
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
rabbitmq:
  host: localhost
  post: 5672
  username: guest
  password: guest

3、缩写接受消息的通道接口

package com.example.springconsumer;

import org.springframework.cloud.stream.annotation.Input;
import org.springframework.messaging.SubscribableChannel;

public interface ReceiveService {
    @Input("myInput")
    SubscribableChannel myInput();
}

4、修改启动类代码

同样绑定消息通道

package com.example.springconsumer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.StreamListener;

@SpringBootApplication
@EnableBinding(ReceiveService.class)
public class SpringConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringConsumerApplication.class, args);
    }

    //订阅myInput通道的消息
    @StreamListener("myInput")
    public void receive(byte[] msg){
        System.out.println("接收到的消息：" + new String(msg));
    }
}

5、测试

（1）检查服务里面的RabbitMQ是否有启动（默认启动）；

（2）启动spring-server（8761端口）；

（3）启动spring-producer（8081端口）；

（4）启动spring-consumer（8080端口）；

（5）浏览器访问http://localhost:8081/send，spring-consumer项目的控制台输出：

接收到的消息：hello world

说明消费者已经可以从消息代理中获取到消息。

四、更换绑定器

上面使用了RabbitMQ作为消息代理，如果使用Kafka，可以更换Maven依赖实现。
在生产者和消费者的pom.xml中，将spring-cloud-starter-stream-rabbit修改为spring-cloud-starter-stream-kafka。

五、Sink、Source与Processor接口

为了简化开发，Spring Cloud Stream内置了3个接口：Sink、Source与Processor。接口定义如下：

public interface Source {
    String OUTPUT = "output";

    @Output("output")
    MessageChannel output();
}
public interface Sink {
    String INPUT = "input";

    @Input("input")
    SubscribableChannel input();
}
public interface Processor extends Source, Sink {
}

通过上面内置接口，不必编写服务接口，生产者绑定通道时加入Source.class，消费者绑定通道时加入Sink.class，因为Processor继承于Sink与Source，也可以只使用Processor。

1、消息生产者代码改写如下：

（1）启动类代码

绑定通道时加入Processor.class

package com.example.springproducer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.messaging.Processor;

@SpringBootApplication
@EnableEurekaClient
@EnableBinding(Processor.class)
public class SpringProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringProducerApplication.class, args);
    }

}

（2）修改配置application.yml

绑定名为input的消息队列，否则消息队列默认为output。

server:
  port: 8081
spring:
  application:
    name: spring-producer
  cloud:
    stream:
      bindings:
        output:
          destination: input
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

（3）删除服务接口SendService

2、消息消费者代码改写如下：

（1）启动类代码

绑定通道时加入Processor.class

package com.example.springconsumer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.stream.annotation.EnableBinding;
import org.springframework.cloud.stream.annotation.StreamListener;
import org.springframework.cloud.stream.messaging.Processor;
import org.springframework.messaging.handler.annotation.SendTo;

@SpringBootApplication
@EnableBinding(Processor.class)
public class SpringConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringConsumerApplication.class, args);
    }

    @StreamListener(Processor.INPUT)
    public void receive(byte[] msg){
        System.out.println("接收到的消息：" + new String(msg));
    }
}

（2）删除服务接口ReceiveService 

重新启动应用，浏览器访问http://localhost:8081/send，spring-consumer项目的控制台输出：

接收到的消息：hello world

六、消费者组

消费者组不同时，会发送给所有的消费者实例。
消费者组相同时，对于发送过来的消息，仅由其中一个消费者实例处理。

1、修改消费者spring-consumer项目的配置application.yml，配置消费者组为groupA

server:
  port: 8080
spring:
  application:
    name: spring-consumer
  cloud:
    stream:
      bindings:
        input:
          group:
            groupA
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

2、仿照上面消费者spring-consumer项目，新建两个消费者项目spring-second-consumer（端口8082）和spring-third-consumer（端口8083），配置application.yml的消费者组都为groupB。

重新启动应用，浏览器多次访问http://localhost:8081/send，可以看到原来消费者spring-consumer都能收到，新加的两个消费者spring-second-consumer（端口8082）和spring-third-consumer（端口8083）会轮询处理。