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http://blog.csdn.net/forezp/article/details/69808079
本文出自方志朋的博客
上一篇文章，讲述了如何通过RestTemplate+Ribbon去消费服务，这篇文章主要讲述如何通过Feign去消费服务。
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9999; 启动eureka-client两次，端口分别为8810、8811.
三、创建一个feign的服务
新建一个spring-boot工程，取名为feign-service，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.lying</groupId>
<artifactId>feign-service</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>feign-service</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.10.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.SR2</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>
</project>
在工程的配置文件application.yml文件，指定程序名为feign-service，端口号为9911，服务注册地址为http://localhost:9999/eureka/ ，代码如下：
server:
port: 9911
eureka:
client:
service-url:
defaultZone: http://localhost:9999/eureka/
spring:
application:
name: feign-service
在程序的启动类FeignServiceApplication，加上@EnableFeignClients注解开启Feign的功能：
package com.lying.feignservice;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
@SpringBootApplication
@EnableFeignClients
@EnableDiscoveryClient
public class FeignServiceApplication {
public static void main(String[] args) {
SpringApplication.run(FeignServiceApplication.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eureka-client服务的“/users/{name}”接口，代码如下：
package com.lying.feignservice.service;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
@FeignClient(value = "eureka-client")
public interface UserService {
@RequestMapping(value = "/users/{name}", method = RequestMethod.GET)
String findUserByName(@PathVariable("name") String name);
}
在Web层的controller层，对外暴露一个”/users/{name}”的API接口，通过上面定义的Feign客户端UserService 来消费服务。代码如下：
package com.lying.feignservice.controller;
import com.lying.feignservice.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
@RestController
public class UserController {
@Autowired
private UserService userService;
@RequestMapping(value = "/users/{name}", method = RequestMethod.GET)
public String fetchUserByName(@PathVariable("name") String name) {
return userService.findUserByName(name);
}
}
启动程序，多次访问http://localhost:9911/getUserInfo?name=Lee浏览器交替显示：
User(id=2, name=Lee, age=23): 8810
User(id=2, name=Lee, age=23): 8811
Feign源码解析：http://blog.csdn.net/forezp/article/details/73480304
本文源码下载：
https://github.com/lyingfromyou/SpringCloudExample
