SpringCloud第三篇-Feign

你的名字 2022-06-07 12:41 193阅读 0赞

### Feign简介 ###

Feign 是一个声明web服务客户端，这便得编写web服务客户端更容易，使用Feign 创建一个接口并对它进行注解，它具有可插拔的注解支持包括Feign注解与JAX-RS注解，Feign还支持可插拔的编码器与解码器，Spring Cloud 增加了对 Spring MVC的注解，Spring Web 默认使用了HttpMessageConverters, Spring Cloud 集成 Ribbon 和 Eureka 提供的负载均衡的HTTP客户端 Feign.

简而言之：

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

### 准备工作 ###

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

### 创建service-feign项目 ###

#### pom ####

<?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">
    
            <artifactId>service-feign</artifactId>
            <groupId>comm.bamboo</groupId>
            <version>1.0-SNAPSHOT</version>
    
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>1.5.2.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>
        </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>

#### yml ####

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

#### java代码 ####

FeignApplication.java

package com.bamboo;
    
    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.feign.EnableFeignClients;
    import org.springframework.context.annotation.Bean;
    import org.springframework.web.client.RestTemplate;
    
    /** * * FeignApplication * * Application */
    @SpringBootApplication
    @EnableDiscoveryClient//向服务中心注册
    @EnableFeignClients//@EnableFeignClients注解开启Feign功能
    public class FeignApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(FeignApplication.class, args);
        }
    
    
    }

SchedualServiceHello.java  
这个接口是整个最重要和注意的地方

*  通过@ FeignClient（“服务名”），来绑定并指定调用哪个服务
 *  RequestMapping中的配置要和提供服务方提供的方法名和RequestMethod一摸一样

因此从 RequestMapping可以看出它是通过http协议进行的远程调用，而dubbo则是通过自定义的协议进行的二进制调用。

package com.bamboo;
    
    import org.springframework.cloud.netflix.feign.FeignClient;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestMethod;
    import org.springframework.web.bind.annotation.RequestParam;
    
    /** * 定义一个feign接口，通过@ FeignClient（“服务名”），来绑定并指定调用哪个服务 * Created by babmoo on 2017/10/21. */
    @FeignClient(value = "service-hello")
    public interface SchedualServiceHello {
    
        //使用的springmvc注解
        @RequestMapping(value = "/hello",method = RequestMethod.GET)
        String sayHiFromClientOne(@RequestParam(value = "name") String name);
    }

HelloController.java

package com.bamboo;
    
    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.RequestParam;
    import org.springframework.web.bind.annotation.RestController;
    
    /** * Created by xialeme on 2017/10/21. */
    @RestController
    public class HelloController {
    
    
        @Autowired
        SchedualServiceHello  schedualServiceHello;
        @RequestMapping(value = "/hello",method = RequestMethod.GET)
        public String sayHi(@RequestParam String name){
            return schedualServiceHello.sayHiFromClientOne(name);
        }
    
    
    }

### 运行服务组件并调用服务 ###

*  运行eureka-server
 *  运行service-hello
 *  修改service-hello的端口8763再次运行
 *  运行service-feign

启动程序，多次访问[http://localhost:8765/hello?name=forezp][http_localhost_8765_hello_name_forezp],浏览器交替显示：

hello from port:8762
    hello from port:8763

显示结果和上一篇的结果一样的，说明至少在形式上他们都进行了轮询方式的负载均衡。其实他们实际都是ribbon模块进行的负载均衡

### 总结 ###

其实通过Feign封装了HTTP调用服务方法，使得客户端像调用本地方法那样直接调用方法，类似Dubbo中暴露远程服务的方式。  
区别在于Dubbo是基于私有二进制协议，而Feign本质上还是个HTTP客户端

[http_localhost_8765_hello_name_forezp]: http://localhost:8765/hello?name=forezp