說到spring-cloud 服務呼叫不的不提dubbo. spring-cloud的服務呼叫是基於http呼叫，dubbo是基於RPC。使用feign就能實現微服務間的方法呼叫。

spring-cloud的服務呼叫一般有兩種，第一種是ribbon+restTemplate，第二種是feign
由於feign預設集成了ribbon，這裡集中介紹feign
基於上一篇文章的例子eureka-client改造
首先新建一個模組feign-client,在pom里加入如下依賴：

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>
    <artifactId>eureka-feign</artifactId
 
>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <file.encoding>UTF8</file.encoding
 
>
        <spring-cloud.version>Finchley.SR2</spring-cloud.version>
    </properties>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
    </parent>

    <dependencies>
        <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>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </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>

增加配置如下
application.properties

server.port=8884
spring.application.name=feignService

eureka.client.service-url.defaultZone=http://localhost:8881/eureka/

Application.java配置如下：

package top.littlematch.feign;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
@RestController
public class FeignApplication {
    public static void main(String[] args){
        SpringApplication.run(FeignApplication.class, args);
    }
    //呼叫的服務名，以介面的方式定義
    @FeignClient("baseService")
    public interface BaseService {
        //呼叫的方法所暴露的url,其實就相當於頁面呼叫方法一樣
        @RequestMapping(value = "/hello", method = RequestMethod.GET)
        public String hello(@RequestParam("name") String name);
    }

    /**
     * 注入該方法，idea這裡可能會報紅
     *  這裡就如dubbo的方法呼叫，只是這裡需重新定義個介面接收方法
     *  基於http會多這一步，但也因為基於http其擴充套件性很強,能輕易實現與其他語言基於http服務呼叫
     */

    @Autowired
    private BaseService baseService;


    @RequestMapping("/hello")
    public String hello(@RequestParam("name")String name){
        //呼叫方法
        return baseService.hello(name);
    }
}

依次啟動eureka-server,eureka-client,feign-client,再呼叫 http://localhost:8884/hello?name=match

瀏覽器返回：

hello! match

gitee程式碼地址：https://gitee.com/leftbehindmatches/spring-cloud-examples/tree/master/eureka-feign