在spring Cloud Netflix栈中，各个微服务都是以HTTP接口的形式暴露自身服务的，因此在调用远程服务时就必须使用HTTP客户端。我们可以使用JDK原生的URLConnection、Apache的Http Client、Netty的异步HTTP Client, Spring的RestTemplate。但是，用起来最方便、最优雅的还是要属Feign了。

Feign简介

Feign是一种声明式、模板化的HTTP客户端。在Spring Cloud中使用Feign, 我们可以做到使用HTTP请求远程服务时能与调用本地方法一样的编码体验，开发者完全感知不到这是远程方法，更感知不到这是个HTTP请求

下面写一个feign的实例:

pom.xml的配置

        <!-- 添加feign 的依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

启动类添加注解:

package com.wenbronk.consumer.feign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
//import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

/**
 * Created by root on 2017/5/20.
 */
@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class MovieFeignApplication {
    public static void main(String[] args) {
        SpringApplication.run(MovieFeignApplication.class, args);
    }
}

3, 编写一个feignClient接口, 以实现远程调用

package com.wenbronk.consumer.feign.feignclient;

import com.wenbronk.consumer.feign.entity.UserEntity;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

/**
 * feign的接口
 * Created by root on 2017/5/20.
 */
@FeignClient("microservice-provider-user")
public interface UserFeignClient {

    /**
     * 不可以使用 getMapping, 或者postMapping注解
     *
     * @param id
     * @return
     * @PathVariable 中 必须有value的值
     */
    @RequestMapping(value = "/simple/{id}", method = RequestMethod.GET)
    public UserEntity findById(@PathVariable("id") Long id);

    @RequestMapping(value = "/user", method = RequestMethod.POST)
    public UserEntity postUser(@RequestBody UserEntity userEntity);

    /**
     * 这儿不会管呗调用的用什么方法
     @PostMapping("/user")
     public User postUser(@RequestBody User user) {
        return user;
     }
     */
    @RequestMapping(value = "/user", method = RequestMethod.GET)
    public UserEntity getUser(UserEntity userEntity);

    /**
     * 如果被调用的方法是对象, 默认是post请求, 对方不可以是get请求
     // 该请求不会成功
     @GetMapping("/get-user")
     public User getUser(User user) {
         return user;
     }
     * @param userEntity
     * @return
     */
    @RequestMapping(value = "/get-user", method = RequestMethod.GET)
    public UserEntity getUserGet(UserEntity userEntity);

}

4, 在controller中进行实验

package com.wenbronk.consumer.feign.controller;

import com.wenbronk.consumer.feign.entity.UserEntity;
import com.wenbronk.consumer.feign.feignclient.UserFeignClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * Created by root on 2017/5/20.
 */
@RestController
public class MovieController {

    @Autowired
    private UserFeignClient userFeignClient;

    @GetMapping("/findUserById/{id}")
    public UserEntity findUserById(@PathVariable Long id) {
        return userFeignClient.findById(id);
    }

    @PostMapping("/getUser")
    public UserEntity getUser(UserEntity user) {
//        return userFeignClient.postUser(user);
        return userFeignClient.getUser(user);
//        return userFeignClient.getUserGet(user);
    }

}

调用的远程服务为: http://www.cnblogs.com/wenbronk/p/6881573.html

中的user服务

使用feign遇到的坑:

1, feign接口中, GetMapping, PostMapping不支持, 必须使用RequestMapping

2, 使用RestFul请求时, @PathVariables("id"), 和变量同名也必须加 "id"

3, 接口中的参数是对象, 默认使用post方法, 不管是否指定 @RequestMapping(method=..)