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9090; 启动service-hi 两次，端口分别为9091 、9092.

三、创建一个feign的服务

新建一个spring-boot工程，取名为serice-feign，在它的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：

<?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>

<groupId>com.jeffrey</groupId>
<artifactId>service-feign</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>

<name>service-feign</name>
<description>Demo project for Spring Boot</description>

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.12.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>1.8</java.version>
    <spring-cloud.version>Edgware.SR3</spring-cloud.version>
</properties>

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

server: port: 10002 spring: application: name: eureka-consumer eureka: client: service-url: defaultZone: http://localhost:8761/eureka

设置feign熔断特性

feign: hystrix: enabled: true

在程序的启动类ServiceFeignApplication ，加上@EnableFeignClients注解开启Feign的功能：

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignApplication {

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


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-provider服务的“/hello”接口，代码如下：

/**
 * Created by Jeffrey on 2018/4/21 0021.
 */
@FeignClient(value="service-provider")  //通过@FeignClient(value="服务名") 定义该接口调用哪项服务
public interface SchedualServiceProvider {
/**
 * 调用service-provider服务的/hello接口，并传name参数
 * @param name  接口调用必须的参数
 * @return
 */
@RequestMapping(value="/hello",method = RequestMethod.GET)
public String sayHello(@RequestParam(value="name") String name);

}


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

/**
 * Created by Jeffrey on 2018/4/21 0021.
 */
@RestController
public class HelloController {
    @Autowired
    private SchedualServiceProvider schedualServiceProvider;
    @RequestMapping(value="/hello",method= RequestMethod.GET)
    public String sayHelli(@RequestParam String name){

     return schedualServiceProvider.sayHello(name);

    }
}

启动程序，多次访问http://localhost:9094/hello?name=jeffrey,浏览器交替显示：