SpringCloud | 第三篇: 服务消费者（Feign）

ゝ一世哀愁。 2022-05-10 10:44 251阅读 0赞

上一篇文章，讲述了如何通过RestTemplate+Ribbon去消费服务，这篇文章主要讲述如何通过Feign去消费服务。

### 一、Feign简介 ###

Feign是一个声明式的伪Http客户端，它使得写Http客户端变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，并和Eureka结合，默认实现了负载均衡的效果。

简而言之：

*  Feign 采用的是基于接口的注解
 *  Feign 整合了ribbon

### 二、准备工作 ###

继续用上一节的工程， 启动eureka-server，端口为8761; 启动service-hi 两次，端口分别为8762 、8773.

### 三、创建一个feign的服务 ###

新建一个spring-boot工程，取名为serice-feign，在它的pom文件引入Feign的起步依赖spring-cloud-starter-feign、Eureka的起步依赖spring-cloud-starter-eureka、Web的起步依赖spring-boot-starter-web，代码如下：

<?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.cimc</groupId>
    	<artifactId>feign</artifactId>
    	<version>0.0.1-SNAPSHOT</version>
    	<packaging>jar</packaging>
    
    	<name>feign</name>
    	<description>Demo project for Spring Boot</description>
    
    	<parent>
    		<groupId>org.springframework.boot</groupId>
    		<artifactId>spring-boot-starter-parent</artifactId>
    		<version>2.0.5.RELEASE</version>
    		<relativePath/> 
    	</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.SR1</spring-cloud.version>
    	</properties>
    
    	<dependencies>
    		<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.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>
    			<dependency>
    				<groupId>org.springframework.cloud</groupId>
    				<artifactId>spring-cloud-openfeign</artifactId>
    				<type>pom</type>
    				<scope>import</scope>
    			</dependency>
    		</dependencies>
    	</dependencyManagement>
    
    	<repositories>
    		<repository>
    			<id>spring-snapshots</id>
    			<name>Spring Snapshots</name>
    			<url>https://repo.spring.io/libs-snapshot</url>
    			<snapshots>
    				<enabled>true</enabled>
    			</snapshots>
    		</repository>
    	</repositories>
    
    	<build>
    		<plugins>
    			<plugin>
    				<groupId>org.springframework.boot</groupId>
    				<artifactId>spring-boot-maven-plugin</artifactId>
    			</plugin>
    		</plugins>
    	</build>
    
    </project>

在工程的配置文件application.yml文件，指定程序名为service-feign，端口号为8765，服务注册地址为[http://localhost:8761/eureka/][http_localhost_8761_eureka] ，代码如下：

eureka:
      client:
        serviceUrl:
          defaultZone: http://localhost:8761/eureka/
    server:
      port: 8765
    spring:
      application:
        name: service-feign

在程序的启动类ServiceFeignApplication ，加上@EnableFeignClients注解开启Feign的功能：

@EnableFeignClients注解未能引入，参考[https://cloud.spring.io/spring-cloud-openfeign/\#quick-start][https_cloud.spring.io_spring-cloud-openfeign_quick-start]

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

定义一个feign接口，通过@ FeignClient（“服务名”），来指定调用哪个服务。比如在代码中调用了service-hi服务的“/hi”接口，代码如下：

/**
     * Created by fangzhipeng on 2017/4/6.
     */
    @Component
    @FeignClient(value = "service-hi")
    public interface SchedualServiceHi {
        @RequestMapping(value = "/hi",method = RequestMethod.GET)
        String sayHiFromClientOne(@RequestParam(value = "name") String name);
    }

在Web层的controller层，对外暴露一个”/hi”的API接口，通过上面定义的Feign客户端SchedualServiceHi 来消费服务。代码如下：

@RestController
    public class HiController {
    
        @Autowired
        SchedualServiceHi schedualServiceHi;
        @RequestMapping(value = "/hi",method = RequestMethod.GET)
        public String sayHi(@RequestParam String name){
            return schedualServiceHi.sayHiFromClientOne(name);
        }
    }

启动程序，多次访问[http://localhost:8765/hi?name=forezp][http_localhost_8765_hi_name_forezp],浏览器交替显示：

> hi forezp,i am from port:8762
> 
> hi forezp,i am from port:8763

Feign源码解析：[http://blog.csdn.net/forezp/article/details/73480304][http_blog.csdn.net_forezp_article_details_73480304]

本文源码下载：  
[https://github.com/forezp/SpringCloudLearning/tree/master/chapter3][https_github.com_forezp_SpringCloudLearning_tree_master_chapter3]

### 五、参考资料 ###

[spring-cloud-feign][]

[http_localhost_8761_eureka]: http://localhost:8761/eureka/
[https_cloud.spring.io_spring-cloud-openfeign_quick-start]: https://cloud.spring.io/spring-cloud-openfeign/#quick-start
[http_localhost_8765_hi_name_forezp]: http://localhost:8765/hi?name=forezp
[http_blog.csdn.net_forezp_article_details_73480304]: http://blog.csdn.net/forezp/article/details/73480304
[https_github.com_forezp_SpringCloudLearning_tree_master_chapter3]: https://github.com/forezp/SpringCloudLearning/tree/master/chapter3
[spring-cloud-feign]: http://projects.spring.io/spring-cloud/spring-cloud.html#spring-cloud-feign