1. 什麼是feign

上個文章,我們是使用restTemplate + Ribbon 來實現分散式服務之間的生產和消費的呼叫的, 這篇文章來講一講SpringCloud分散式服務之間呼叫的另一個方案, feign

Feign是一個宣告式的偽Http客戶端，它使得寫Http客戶端變得更簡單。使用Feign，只需要建立一個介面並註解。它具有可插拔的註解特性，可使用Feign 註解和JAX-RS註解。Feign支援可插拔的編碼器和解碼器。Feign預設集成了Ribbon，並和Eureka結合，預設實現了負載均衡的效果

重點:

• Feig採用的是基於介面的註解
• Feign整合了Ribbon

2. 建立feign的服務

這裡接著上一篇使用Ribbon的文章繼續進行
這個時候我們已經有:
1. eurekaServer — 註冊中心
2. eureka-client-01 — 生產者,客戶端
3. service-ribbon — 使用ribbon呼叫eureka-client-01方法的消費者

新建一個spring-boot工程,(怕麻煩的話其實可以直接複製上面的service-ribbon, 把所有ribbon換成feign, pom檔案改吧改吧就好了)

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>
    <packaging>jar</packaging>
    <artifactId
 
>service-feign</artifactId>


    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.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>
    </properties>

    <dependencies>
        <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>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Dalston.RC1</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>

    <repositories>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>



</project>

application.yml配置如下

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
spring:
  application:
    name: service-feign
server:
  port: 8086

啟動類上面打上@EnableFeignClients註解開啟Feign的功能

package com.zgd.springcloud.eurekaClient;

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.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;


/**
 * eureka client 客戶端
 */
@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication(scanBasePackages = "com.zgd.springcloud.eurekaClient")
public class FeignApp {

    public static void main(String[] args) {
        SpringApplication.run(FeignApp.class, args);
    }

}

這裡和ribbon區別的地方就來了

ribbon是直接定義一個serviceImpl, 在裡面用restTemplate去訪問暴露在外面的其他服務提供者的mvc介面

feign直接定義一個介面,通過@ FeignClient（“服務名”），來指定呼叫哪個服務
下面註解中的@RequestMapping的value都是eureka-client-01模組需要呼叫的方法的路由

package com.zgd.springcloud.eurekaClient.interf;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * @FeignClient value是指定的服務提供者在eurekaServer中的服務名,也就是eureka-client-01的applicationName: client01
 */
@FeignClient(value = "client01")
@Component
public interface FeignService{

    /**
     * 這裡還是訪問的eureka-client-01的
     *      com.zgd.springcloud.eurekaClient.controller.ProducerController
     *      的hello方法的路由
     * @param name
     * @return
     */
    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    String hiService(@RequestParam(value = "name") String name);
}

在Web層的controller層, 對外暴露一個api介面

package com.zgd.springcloud.eurekaClient.controller;

import com.zgd.springcloud.eurekaClient.interf.FeignService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
public class FeignController {

    @SuppressWarnings("SpringJavaInjectionPointsAutowiringInspection")

    @Autowired
    FeignService feignService;
    /**
     * 通過service層,用restTemplate訪問Client01路由,間接呼叫了Client01工程的方法
     * @param name
     * @return
     */
    @RequestMapping(value = "/getHi",method = RequestMethod.GET)
    public String getHi(@RequestParam String name) {
        return feignService.hiService( name );
    }

}

這個時候因為介面沒有實現類,不用擔心會報錯空指標異常, 前提是你的app啟動類上確實用了@EnableFeignClients

4. 啟動程式

1. 啟動eurekaServer
2. 啟動eureka-client-01, 更改埠號, 再次啟動
3. 啟動service-feign

多次訪問,可以看到輪詢呼叫了兩個埠

5.原始碼