SpringCloud第三篇-Feign

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/> <!-- 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>
    </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>

        <!-- spring boot jar -->
        <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,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