前言：一般情况下我们通常使用RestTemplate来实现声明式远程调用，但是当参数过多，那么效率就会变得很低，并且难以维护，所以在微服务当中也有声明式Rest调用的组件Feign
一、Feign简介
Feign是Netflix开发的声明式、模板化的http客户端，Feign可以帮我们更加便捷、优雅地调用HTTP API。在SpringCloud中使用Feign非常简单，创建一个接口，并在接口上加上注解，就完成了声明式调用；
二、Feign与SpringCloud的整合简单使用
注：本次学习记录是基于之前的Eureka介绍和Ribbon介绍之上实践，这里只展示关键代码，其余代码可在代码示例中查看；
1、创建基于Eureka和Ribbon的服务端和两个客户端生产者、消费者：
Server：
pom.xml
application.properties
ServerApplication.java
Client生产者：
pom.xml
application.properties
ClientApplication.java
ClientController.java
2、在消费者module中的maven依赖中添加相关依赖库，创建Feign访问接口，并注解，通过识别Eureka提供的应用名称，来找对应的请求路径：
pom.xml：
<?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.cn</groupId>
<artifactId>eureka-feign-client</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>1.8</java.version>
</properties>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.13.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-ribbon</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-feign</artifactId>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Edgware.SR3</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<!-- 添加spring-boot的maven插件 -->
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.properties:
server.port=8762 spring.application.name=client-8762 eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
Feign接口：
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
@FeignClient(name = "CLIENT-87")
public interface UserFeign {
@RequestMapping("/getUser")
public String getUser();
}
FeignController：
package com.cn.controller;
import com.cn.feign.UserFeign;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
/**
* @program: springcloud-example
* @description:
* @author:
* @create: 2018-06-15 15:55
**/
@RestController
public class FeignController {
@Autowired
private LoadBalancerClient loadBalancerClient;
@Autowired
private RestTemplate restTemplate;
@Autowired
private UserFeign userFeign;
@RequestMapping("/getUser")
public String getUser() {
return userFeign.getUser();
}
@GetMapping("/loadInstance")
public String loadInstance() {
ServiceInstance choose = this.loadBalancerClient.choose("client-87");
System.out.println(choose.getServiceId()+":"+choose.getHost()+":"+choose.getPort());
return choose.getServiceId() + ":" + choose.getHost() + ":" + choose.getPort();
}
}
在ClientApplication.java启动类中加入@EnableFeignClients注解：
package com.cn;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
/**
* @program: springcloud-example
* @description:
* @author:
* @create: 2018-06-15 15:51
**/
@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ClientApplication {
public static void main(String[] args) {
SpringApplication.run(ClientApplication.class, args);
}
/**
* @Description:
* @Param:
* @return:
* @Author:
* @Date: 2018/6/15
*/
@Bean
@LoadBalanced
public RestTemplate getRestTemplate() {
return new RestTemplate();
}
}
3、分别启动Server、Client生产者、Client消费者，并调用访问http://localhost:8761、http://localhost:8762/getUser，如图：
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调用成功！