什麼是 Feign

• Feign 即：基於介面的服務呼叫，是一個宣告式的 Web Service 客戶端
• Feign 集成了 Ribbon 可以使用 Ribbon 的負載均衡演算法

Feign 的使用

1. 新建 Module：spring-cloud-consumer-dept-feign-80

2. 編寫 pom 引入依賴

   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">
       <parent>
           <artifactId>spring-cloud-netflix</artifactId>
           <groupId>com.kaishen</groupId>
           <version>1.0-SNAPSHOT</version>
       </parent>
       <modelVersion>4.0.0</modelVersion>
   
       <artifactId>spring-cloud-consumer-dept-feign-80</artifactId>
   
       <properties>
           <maven.compiler.source>8</maven.compiler.source>
           <maven.compiler.target>8</maven.compiler.target>
       </properties>
   
       <!-- 引入該模組所需依賴 -->
       <dependencies>
           <!-- api -->
           <dependency>
               <groupId>com.kaishen</groupId>
               <artifactId>spring-cloud-api</artifactId>
               <version>1.0-SNAPSHOT</version>
           </dependency>
   
           <!-- lombok -->
           <dependency>
               <groupId>org.projectlombok</groupId>
               <artifactId>lombok</artifactId>
           </dependency>
   
           <!--SpringBoot Web-->
           <dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-web</artifactId>
           </dependency>
   
           <!-- SpringBoot 監控 -->
           <dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-actuator</artifactId>
           </dependency>
   
           <!-- Eureka Client -->
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-starter-eureka</artifactId>
           </dependency>
   
           <!-- Feign -->
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-starter-feign</artifactId>
           </dependency>
       </dependencies>
   </project>
    
   

3. 編寫 application.yml 配置註冊中心

   application.yml

   server:
     port: 80
   
   # Eureka 配置
   eureka:
     client:
       register-with-eureka: false # Consumer 無需註冊
       service-url:
         defaultZone: http://eureka7001.com:7001/eureka/,http://eureka7002.com:7002/eureka/,http://eureka7003.com:7003/eureka/
   

4. 編寫啟動類，開啟 Feign 掃描：@EnableFeignClients(basePackages = {"com.kaishen"})

   DeptConsumerFeignApplication80

   package com.kaishen;
   
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
   import org.springframework.cloud.openfeign.EnableFeignClients;
   
   /**
    * 部門服務消費者啟動類
    *  Feign 實現遠端呼叫
    * @author : toby
    * Create in 11:23 2022/5/9
    */
   @SpringBootApplication
   @EnableEurekaClient
   @EnableFeignClients(basePackages = {"com.kaishen"})
   public class DeptConsumerFeignApplication80 {
   
       public static void main(String[] args) {
           SpringApplication.run(DeptConsumerFeignApplication80.class, args);
       }
   }
    
   

5. 定義介面，開啟註解：@FeignClient(value = "SPRING-CLOUD-PROVIDER-DEPT", contextId = "1")

   DeptFeignService

   package com.kaishen.feign.service;
   
   import com.kaishen.pojo.Dept;
   import org.springframework.cloud.openfeign.FeignClient;
   import org.springframework.stereotype.Component;
   import org.springframework.web.bind.annotation.GetMapping;
   import org.springframework.web.bind.annotation.PathVariable;
   
   /**
    * 部門客戶端服務
    * @author : toby
    * Create in 11:26 2022/5/9
    */
   @Component
   @FeignClient(value = "SPRING-CLOUD-PROVIDER-DEPT", contextId = "1")
   public interface DeptFeignService {
   
       /**
        * 根據部門編號查詢部門資訊
        * @param id 部門編號
        * @return 返回部門資訊
        */
       @GetMapping("/feign/dept/get/{id}")
       Dept feignQueryDeptById(@PathVariable("id") Long id);
   }
   

   注意：

   • 通過 @FeignClient 註解呼叫同一個微服務時，會出現 Bean 重複註冊的情況，可使用 contextId = "1" 來區分其唯一性
   • // 此處的 @PathVariable 註解，必須指定("id")

6. 編寫 Controller 使用 Feign 實現遠端呼叫

   DeptConsumerFeignController

   package com.kaishen.controller;
   
   import com.kaishen.feign.service.DeptFeignService;
   import com.kaishen.feign.service.DeptHystrixDemotionService;
   import com.kaishen.feign.service.DeptHystrixFusingService;
   import com.kaishen.pojo.Dept;
   import lombok.extern.slf4j.Slf4j;
   import org.springframework.web.bind.annotation.GetMapping;
   import org.springframework.web.bind.annotation.PathVariable;
   import org.springframework.web.bind.annotation.RequestMapping;
   import org.springframework.web.bind.annotation.RestController;
   
   import javax.annotation.Resource;
   
   /**
    * 部門服務消費者 Feign 控制層
    * @author : toby
    * Create in 11:43 2022/5/9
    */
   @RestController
   @Slf4j
   public class DeptConsumerFeignController {
   
       /**
        * Feign 實現遠端服務呼叫
        */
       @Resource
       private DeptFeignService deptFeignService;
   
       // region Feign 實現遠端服務呼叫
       /**
        * 根據部門編號查詢部門資訊
        *  -- Feign 實現遠端服務呼叫
        * @param id 部門編號
        * @return 返回部門資訊
        */
       @RequestMapping("/feign/dept/get/{id}")
       public Dept feignQueryDeptById(@PathVariable Long id) {
           // Feign 實現遠端服務呼叫
           Dept dept = deptFeignService.feignQueryDeptById(id);
   
           log.info("Feign 查詢結果：" + dept);
   
           return dept;
       }
       // endregion
   }