springcloud（五）服务消费者（Feign）负载均衡

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本文介绍了如何在SpringCloud中使用Feign作为服务消费者实现负载均衡。首先，配置了Eureka Server和两个service-client实例。接着，创建了一个名为service-feign的新项目，添加了必要的依赖，并在application.yml中进行了配置。通过@EnableFeignClients注解启用Feign功能，定义了一个Feign接口指明调用service-client服务。在Web层Controller中，使用该Feign客户端调用服务，通过浏览器访问验证了负载均衡的效果，每次请求会交替显示来自不同端口的服务响应。

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1.准备工作（设置idea开启多个springboot实例）https://blog.youkuaiyun.com/qq_42014192/article/details/89245306

启动eureka-server，端口为8761; 启动service-client 两次，端口分别为8762 、8773.

2.新建一个spring-boot工程，取名为：service-feign;

https://blog.youkuaiyun.com/qq_42014192/article/details/88742559

3.pom.xml依赖

<?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 http://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>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>springcloud_serice-feign_demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springcloud_serice-feign_demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR1</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>

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

4.配置文件application.yml如下：

server:
  port: 8765 #服务端口

spring:
  application:
    name: service-feign

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

5.在程序的启动类@EnableFeignClients注解开启Feign的功能

@SpringBootApplication
//通过注解@EnableEurekaClient 表明自己是一个eurekaclient
@EnableEurekaClient
//通过@EnableDiscoveryClient向服务中心注册
@EnableDiscoveryClient
//加上@EnableFeignClients注解开启Feign的功能
@EnableFeignClients
public class SpringcloudSericeFeignDemoApplication {

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

}

6.定义一个feign接口，通过@ FeignClient（“服务名”），来指定调用哪个服务。比如在代码中调用了service-client服务的“/client”接口，代码如下：

@FeignClient(value = "service-client")
public interface HelloService {

    @RequestMapping(value = "/client",method = RequestMethod.GET)
     String hiService(@RequestParam(value = "name") String name);
}

7.在Web层的controller层，对外暴露一个"/client"的API接口，通过上面定义的Feign客户端SchedualServiceHi 来消费服务。代码如下：

@RestController
public class HelloController {

    @Autowired
    private HelloService helloService;

    @GetMapping(value = "/client")
    public String client(@RequestParam String name){
        return helloService.clientService(name);
    }
}

8.在浏览器上多次访问http://localhost:8765/client?name=forezp，浏览器交替显示：

client forezp,i am from port:8762
client forezp,i am from port:8763