一、Feign簡介

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。

簡而言之：

• Feign 採用的是基於介面的註解
• Feign 整合了ribbon

二、準備工作

繼續用上一節的工程， 啟動eureka-server，埠為8761; 啟動service-hi 兩次，埠分別為8762 、8773.

三、建立一個feign的服務

Idea右鍵新增專案，和建立Eureka專案型別，最後選擇Feign 如下圖

新建一個spring-boot 2.0工程，取名為serice-feign，在它的pom檔案引入Feign的起步依賴spring-cloud-starter-openfeign
、Eureka的起步依賴spring-cloud-starter-eureka、Web的起步依賴spring-boot-starter-web，程式碼如下：

<?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.example</groupId>
   <artifactId>service-feign</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>
 
jar</packaging>

   <name>service-feign</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.0.2.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>
      <spring-cloud.version>Finchley.RC2</spring-cloud.version>
   </properties>

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

   <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>

eureka.client.service-url.defaultZoon=http://localhost:8761/eureka
server.port=8765
spring.application.name=service-feign

在程式的啟動類ServiceFeignApplication ，加上@EnableFeignClients註解開啟Feign的功能：

package com.example.servicefeign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@EnableDiscoveryClient
@EnableFeignClients
@EnableEurekaClient
@SpringBootApplication
public class ServiceFeignApplication {

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


}

定義一個feign介面，通過@ FeignClient（“服務名”），來指定呼叫哪個服務。比如在程式碼中呼叫了service-hi服務的“/hi”介面，程式碼如下：

package com.example.servicefeign.service;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import sun.awt.SunHints;

/**
 * Author:   linjunit
 * Version：
 * Date:     2018/6/12 0012
 * Description:
 * Modification  History:
 * Date            Author            Version            Description
 * --------------------------------------------------------------
 * Why & What is modified:
 */
@FeignClient("SERVICE-HI")
public interface SchedualServiceHi {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHi();
}

在Web層的controller層，對外暴露一個”/hi”的API介面，通過上面定義的Feign客戶端SchedualServiceHi 來消費服務。程式碼如下：

package com.example.servicefeign.controller;

import com.example.servicefeign.service.SchedualServiceHi;
import com.netflix.discovery.converters.Auto;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

/**
 * Author:   linjunit
 * Version：
 * Date:     2018/6/12 0012
 * Description:
 * Modification  History:
 * Date            Author            Version            Description
 * --------------------------------------------------------------
 * Why & What is modified:
 */
@RestController
public class ServiceHiController {
    @Autowired
private SchedualServiceHi schedualServiceHi;

    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    public String sayHi(){
      return   schedualServiceHi.sayHi();
    }
}

訪問Eureka服務端可以看到fegin被註冊

這是埠為：8762例項專案

這是埠為：8763例項專案