SpringCloud |第三篇: 服务消费者（Feign+REST）

一、Feign简介

    Feign是Netflix开发的声明式、模版化的HTTP伪客户端。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。

二、准备工作

    继续用上一节的工程， 启动eureka-server，端口为1001; 启动user-service及user-service1服务，端口分别为8084、8085.

三、创建Feign服务器

    新建一个feign-server服务器

    pom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.example</groupId>
	<artifactId>da-feign-server</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>da-feign-server</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.0.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>
		<spring-cloud.version>Finchley.M8</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-openfeign</artifactId>
		</dependency>
		<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-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>${spring-cloud.version}</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>

    在工程的配置文件application.yml文件，指定程序名为feign-service，端口号为3001，服务注册地址为http://localhost:8761/eureka/ ，代码如下：

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:1001/eureka/
  instance:
    lease-renewal-interval-in-seconds: 30
server:
  port: 3001
spring:
  application:
    name: feign-service

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

@EnableFeignClients
@EnableEurekaClient
@SpringBootApplication
public class DaFeignServerApplication {
	public static void main(String[] args) {
		SpringApplication.run(DaFeignServerApplication.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：

@FeignClient(value = "user-service")
public interface HiService {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String getHi(@RequestParam(value = "name") String name);
}

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

@RestController
public class HiController {
    @Autowired
    HiService hiService;

    @RequestMapping(value = "/getHi",method = RequestMethod.GET)
    public String getHi(@RequestParam String name){
        return hiService.getHi(name);
    }
}

    启动程序，多次访问http://localhost:3001/getHi?name=zhangsan,浏览器交替显示：

四、源码下载

    FeignServer源码下载：https://gitee.com/Clarences/Feign-Service