什麼是Feign？

        Feign是受到Retrofit，JAXRS-2.0和WebSocket的影響，它是一個java的到http客戶端繫結的開源專案。 Feign的主要目標是將Java Http 客戶端變得簡單。

推薦部落格：

常見錯誤：

1、Spring Cloud服務消費者使用Feign，不識別@EnableFeignClients 註解解決辦法

 查閱資料後是Spring Cloud對Feign的支援由org.springframework.cloud:spring-cloud-netflix-core 移到org.springframework.cloud:spring-cloud-openfeign-core下。

     報錯資訊：cannot resolve sysmol EnableFeignClients

    解決方案：

    更改Spring Cloud的版本Finchley.RC2換為Dalston.RC1由於Finchley.RC2使用需要Spring Boot2.0，這裡需要把Spring Boot版本換到1.5即可

<dependencies>
   <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-dependencies</artifactId>
      <version>Dalston.RC1</version>
      <type>pom</type>
      <scope>import</scope>
   </dependency>
</dependencies>
 

一、建立服務消費者

    2、專案pom.xml 新增

<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-feign</artifactId>
		</dependency>

完整pom.xml

<?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.serverfeign</groupId>
	<artifactId>serverfeign</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>serverfeign</name>
	<description>Demo project for Spring Boot</description>

	<!--<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.2.RELEASE</version>
		<relativePath/> <!– lookup parent from repository –>
	</parent>-->
	<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>
		<spring-cloud.version>Finchley.RC2</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</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-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>-->

	<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>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>-->
		<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>
 

    3、編寫服務消費Service和Controller

        通過@ FeignClient（“服務名”），來指定呼叫哪個服務

package com.serverfeign.serverfeign.service;

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;


/**
 * 通過@FeignClient（“服務名”），來指定呼叫哪個服務
 * Created by zhoujh on 2018/6/04
 */
@FeignClient(value = "hello-service")
public interface HelloService {
    @RequestMapping(value = "/hi",method = RequestMethod.GET)
    String sayHiFromClientOne(@RequestParam(value = "name") String name);
}

package com.serverfeign.serverfeign.controller;

import com.serverfeign.serverfeign.service.HelloService;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.web.bind.annotation.*;

@RestController

public class HelloController {

@Autowired

HelloService helloService;

@RequestMapping(value = "/hi",method = RequestMethod.GET)

@ResponseBody

public String HiFeign(@RequestParam String name){

return helloService.sayHiFromClientOne(name);

}

}

4、修改配置檔案

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

5、修改啟動類

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

package com.serverfeign.serverfeign;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ServerfeignApplication {

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

二、啟動服務註冊中心、服務提供者(2個)、服務消費者(Feign)

三、重新整理消費者，檢視服務提供者後臺列印，此時已經完成了消費的負載均衡(這裡採用了輪詢策略)

Spring Boot與Spring Cloud學習使用可參看筆者部落格