前言

Spring Cloud里的远程服务调用采用两种方式，一种是RestTemplate，另一种是Feign。两种方式都可以用Ribbon实现负载均衡，其中Feign自带了Ribbon。

开始创建

pom.xml

<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.asiainfo.aigov</groupId>
    <artifactId>consumer-feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>consumer-feign</name>
    <url>http://maven.apache.org</url>
    
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
    </properties>
    
    <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>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>
</project>

application.yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8764
spring:
  application:
    name: consumer-feign

ConsumerFeignApplication

RestTemplate上加@LoadBalanced表示开启负载均衡

package com.asiainfo.aigov.consumer_feign;

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.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication
public class ConsumerFeignApplication {

    public static void main(String[] args) {
        SpringApplication.run(ConsumerFeignApplication.class, args);
    }
    
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
    
}

IHelloService

采用Feign方式调用远程服务，Feign也可称为伪HTTP客户端。@FeignClient后面是服务名，@RequestParam("name")必须有，不然值传不过去。另外，接口的方法名和参数不一定要和实际调用的方法一样，调用方法是根据RequestMapping，参数可以多也可以少，这点和dubbo有区别。

package com.asiainfo.aigov.consumer_feign.service;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient("eureka-client")
public interface IHelloService {

    @RequestMapping("/hello")
    String hello(@RequestParam("name") String name);
    
}

HelloController

package com.asiainfo.aigov.consumer_feign.web.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.asiainfo.aigov.consumer_feign.service.IHelloService;

@RestController
public class HelloController {

    @Autowired
    private IHelloService helloService;
    
    @Autowired
    private RestTemplate restTemplate;
    
    @RequestMapping("/hello")
    public String hello(String name) {
        return helloService.hello(name);
    }
    
    @RequestMapping("/hello2")
    public String hello2(String name) {
        return restTemplate.getForObject("http://eureka-client/hello?name="+name, String.class);
    }
    
}