上一篇文章，講述瞭如何通過RestTemplate+Ribbon去消費服務，這篇文章主要講述如何通過Feign去消費服務。

一、Feign簡介

Feign是一個宣告式的偽Http客戶端，它使得寫Http客戶端變得更簡單。使用Feign，只需要建立一個介面並註解。它具有可插拔的註解特性，可使用Feign 註解和JAX-RS註解。Feign支援可插拔的編碼器和解碼器。Feign預設集成了Ribbon，並和Eureka結合，預設實現了負載均衡的效果。

簡而言之：

• Feign 採用的是基於介面的註解
• Feign 整合了ribbon

二、準備工作

繼續用上一節的工程， 啟動eureka-server，埠為8761; 啟動service-hi 兩次，埠分別為8762 、8773.

三、建立一個feign的服務

新建一個spring-boot工程，取名為serice-feign，在它的pom檔案引入Feign的起步依賴spring-cloud-starter-feign、Eureka的起步依賴spring-cloud-starter-eureka、Web的起步依賴spring-boot-starter-web，程式碼如下：

<?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/> <!-- 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.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>
 

在工程的配置檔案application.yml檔案，指定程式名為service-feign，埠號為8765，服務註冊地址為http://localhost:8761/eureka/ ，程式碼如下：

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

在程式的啟動類ServiceFeignApplication ，加上@EnableFeignClients註解開啟Feign的功能：

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServiceFeignApplication {

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

定義一個feign介面，通過@ FeignClient（“服務名”），來指定呼叫哪個服務。比如在程式碼中呼叫了service-hi服務的“/hi”介面，程式碼如下：

/**
 * 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層的controller層，對外暴露一個”/hi”的API介面，通過上面定義的Feign客戶端SchedualServiceHi 來消費服務。程式碼如下：

@RestController
public class HiController {

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

hi forezp,i am from port:8762

hi forezp,i am from port:8763

五、參考資料