一、Feign简介

Feign是一个声明式的伪Http客户端，它使得写Http客户端变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，并和Eureka结合，默认实现了负载均衡的效果。
简而言之：

Feign 采用的是基于接口的注解
Feign 整合了ribbon

二、准备工作

继续用上一节的工程，启动eureka-server，端口为8761; 启动service-hi 两次，端口分别为8762 、8773.

三、创建一个feign的服务

3.1、新建一个spring-boot工程，取名为service-feign

image.png

3.2、在pom文件引入Feign的起步依赖spring-cloud-starter-feign、Eureka的起步依赖spring-cloud-starter-eureka、Web的起步依赖spring-boot-starter-web，代码如下：

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.13.RELEASE</version>
        <relativePath/> 
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.7</java.version>
        <spring-cloud.version>Dalston.SR1</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-eureka-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</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>

3.3、在工程的配置文件application.properties文件，指定程序名为service-feign，端口号为8765，服务注册地址为http://localhost:8761/eureka/，代码如下：

eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/
server.port=8765
spring.application.name=service-feign

3.4、在程序的启动类加上@EnableFeignClients注解开启Feign的功能：

@ComponentScan(basePackages = {"com.feign"})
@EnableFeignClients(basePackages = "com.feign")
@EnableDiscoveryClient
@SpringBootApplication
public class SpringcloudfeignApplication {

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

3.5、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-hello服务的“/hello”接口，代码如下：

@FeignClient(value = "SERVICE-HELLO")
public interface HelloService {

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

3.6、在Web层的controller层，对外暴露一个”/hi”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
    HelloService helloService;

    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    public String sayHi(@RequestParam String name){
        return helloService.sayHelloFromClientOne(name);
    }

}

3.7、启动程序，多次访问http://localhost:8765/hello?name=abc,浏览器交替显示：