Springcloud學習（六）Feign的使用-聲明式調用

what is feign?

     feign是一個http調用的輕量級框架。可以以java接口的方式調用http請求。簡化了傳統的自己封裝構造對象發送http請求調用service。通過使用註解將請求模板化當實際調用的時候，傳入參數，根據參數再應用到請求上，進而轉化成真正的請求，這種請求相對而言比較直觀。

     github源碼地址：https://github.com/Jacwo/feign-customer.git

開始

1. 使用idea新建一個maven項目 可以使用spring Initializr
2. 替換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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
       <modelVersion>4.0.0</modelVersion>
   
       <groupId>com.yyl</groupId>
       <artifactId>feign-customer</artifactId>
       <version>0.0.1-SNAPSHOT</version>
       <name>feign-customer</name>
       <description>Demo project for Spring Boot</description>
   
       <parent>
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter-parent</artifactId>
           <version>Dalston.SR5</version>
           <relativePath/>
       </parent>
   
       <dependencies>
           <!-- Hystrix，Feign是基於Hystrix的-->
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-starter-hystrix</artifactId>
           </dependency>
           <!-- Eureka依賴，連接註冊中心的都需要有這個依賴 -->
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-starter-eureka</artifactId>
           </dependency>
           <!-- Feign依賴，聲明式開發 -->
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-starter-feign</artifactId>
           </dependency>
           <!-- SpringMVC依賴 -->
           <dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-web</artifactId>
           </dependency>
       </dependencies>
   
       <build>
           <plugins>
               <plugin>
                   <groupId>org.springframework.boot</groupId>
                   <artifactId>spring-boot-maven-plugin</artifactId>
               </plugin>
               <plugin>
                   <groupId>org.apache.maven.plugins</groupId>
                   <artifactId>maven-compiler-plugin</artifactId>
                   <configuration>
                       <source>1.8</source>
                       <target>1.8</target>
                   </configuration>
               </plugin>
           </plugins>
       </build>
   </project>
   

    

3. 編寫啓動類

   package com.yyl.feign;
   
   import org.springframework.boot.SpringApplication;
   import org.springframework.boot.autoconfigure.SpringBootApplication;
   import org.springframework.cloud.netflix.feign.EnableFeignClients;
   
   @EnableFeignClients
   @SpringBootApplication
   public class FeignCustomerApplication {
   
       public static void main(String[] args) {
           SpringApplication.run(FeignCustomerApplication.class, args);
       }
   
   }
   

    

4. 編寫controller

   package com.yyl.feign.controller;
   
   import com.yyl.feign.api.HelloApi;
   import org.springframework.beans.factory.annotation.Autowired;
   import org.springframework.stereotype.Controller;
   import org.springframework.web.bind.annotation.GetMapping;
   import org.springframework.web.bind.annotation.RequestMapping;
   import org.springframework.web.bind.annotation.ResponseBody;
   
   /**
    * author:yangyuanliang Date:2019-08-20 Time:13:43
    **/
   @Controller
   @RequestMapping("feign")
   public class HelloController {
       @Autowired
       private HelloApi helloApi;
       @GetMapping("/hello")
       @ResponseBody
       public String sayHello(){
           return helloApi.hello();
       }
   }
   

    

5. 編寫接口 @FeignClient註解當掃描到該註解的時候，會爲該接口生成一個動態代理類。在代理類中會根據@RequestMapping組合成請求的url路徑。在加上eureka的ribbon自動負載均衡尋找真正的服務地址和url拼接。封裝http發送請求。返回相應結構

   package com.yyl.feign.api;
   
   import org.springframework.cloud.netflix.feign.FeignClient;
   import org.springframework.web.bind.annotation.RequestMapping;
   import org.springframework.web.bind.annotation.RequestMethod;
   
   /**
    * author:yangyuanliang Date:2019-08-20 Time:13:42
    *
    * @author yangyuanliang*/
   @FeignClient(value = "hello-service")
   public interface HelloApi {
       @RequestMapping(value = "/hello",method = RequestMethod.GET)
       String hello();
   }
   

   啓動測試：

6. 1.啓動註冊中心eureka-server

7. 2.啓動服務提供者eureka-server-provider

8. 3.啓動feign消費端 eureka-customer

9. 4.打開瀏覽器訪問 http://localhost:9001/feign/hello

10.