SpringCloud教程 | 第二篇: 服务消费者（Feign）

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

Idea右键添加项目，和创建Eureka项目类型，最后选择Feign 如下图

新建一个spring-boot 2.0工程，取名为serice-feign，在它的pom文件引入Feign的起步依赖spring-cloud-starter-openfeign
、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>4.0.0modelVersion>

   <groupId>com.examplegroupId>
   <artifactId>service-feignartifactId>
   <version>0.0.1-SNAPSHOTversion>
   <packaging>jarpackaging>

   <name>service-feignname>
   <description>Demo project for Spring Bootdescription>

   <parent>
      <groupId>org.springframework.bootgroupId>
      <artifactId>spring-boot-starter-parentartifactId>
      <version>2.0.2.RELEASEversion>
      <relativePath/> 
   parent>

   <properties>
      <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
      <project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>
      <java.version>1.8java.version>
      <spring-cloud.version>Finchley.RC2spring-cloud.version>
   properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.cloudgroupId>
         <artifactId>spring-cloud-starter-openfeignartifactId>
      dependency>
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-clientartifactId>
        dependency>
      <dependency>
         <groupId>org.springframework.bootgroupId>
         <artifactId>spring-boot-starter-testartifactId>
         <scope>testscope>
      dependency>
      <dependency>
         <groupId>org.springframework.bootgroupId>
         <artifactId>spring-boot-starter-webartifactId>
      dependency>
      <dependency>
         <groupId>org.springframework.cloudgroupId>
         <artifactId>spring-cloud-starter-eurekaartifactId>
      dependency>
   dependencies>

   <dependencyManagement>
      <dependencies>
         <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-dependenciesartifactId>
            <version>${spring-cloud.version}version>
            <type>pomtype>
            <scope>importscope>
         dependency>
      dependencies>
   dependencyManagement>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-maven-pluginartifactId>
         plugin>
      plugins>
   build>

   <repositories>
      <repository>
         <id>spring-milestonesid>
         <name>Spring Milestonesname>
         <url>https://repo.spring.io/milestoneurl>
         <snapshots>
            <enabled>falseenabled>
         snapshots>
      repository>
   repositories>


project>

在工程的配置文件application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.service-url.defaultZoon=http://localhost:8761/eureka

server.port=8765

spring.application.name=service-feign

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

package com.example.servicefeign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@EnableDiscoveryClient
@EnableFeignClients
@EnableEurekaClient
@SpringBootApplication
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-hi服务的“/hi”接口，代码如下：

package com.example.servicefeign.service;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import sun.awt.SunHints;

/**
 * Author:   linjunit
 * Version：
 * Date:     2018/6/12 0012
 * Description:
 * Modification  History:
 * Date            Author            Version            Description
 * --------------------------------------------------------------
 * Why & What is modified:
 */
@FeignClient("SERVICE-HI")
public interface SchedualServiceHi {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHi();
}

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：

package com.example.servicefeign.controller;

import com.example.servicefeign.service.SchedualServiceHi;
import com.netflix.discovery.converters.Auto;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

/**
 * Author:   linjunit
 * Version：
 * Date:     2018/6/12 0012
 * Description:
 * Modification  History:
 * Date            Author            Version            Description
 * --------------------------------------------------------------
 * Why & What is modified:
 */
@RestController
public class ServiceHiController {
    @Autowired
    private SchedualServiceHi schedualServiceHi;

    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    public String sayHi(){
      return   schedualServiceHi.sayHi();
    }
}

访问Eureka服务端可以看到fegin被注册

启动程序，多次访问http://localhost:8765/hi,浏览器交替显示：

这是端口为：8762实例项目

这是端口为：8763实例项目