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。

1.Feign概述

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

2.準備工作

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.springcloud</groupId>
    <artifactId>service-feign</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

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

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.0.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>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <!--引入feign-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</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>Finchley.RELEASE</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>


</project>

 

在工程的配置檔案application.yml檔案，指定程式名為service-feign-consumer，埠號為9003，服務註冊地址為http://localhost:8888/eureka/ ，程式碼如下

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8888/eureka/

server:
  port: 9003

spring:
  application:
    name: service-feign-consumer

在程式的啟動類ServiceFeignApplication上加 ，@EnableDiscoveryClient //向服務中心註冊;並且向程式ioc注入一個bean和@EnableFeignClients //開啟feign的功能的註解

package com.springcloud.servicefeign;

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

@SpringBootApplication
@EnableDiscoveryClient //向服務中心註冊;並且向程式ioc注入一個bean
@EnableFeignClients //開啟feign的功能
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-cart服務的“/hi”介面，程式碼如下：

package com.springcloud.servicefeign.feign;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;

/**
 * @PACKAGE_NAME com.springcloud.servicefeign.feign
 * @PROJECT_NAME service-feign
 * @建立人 huang
 * @建立時間 2018/11/27
 */
@FeignClient(value = "service-cart")
public interface SchedualServiceHi {

    /**
     * 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-cart服務的“/hi”介面
     */
    @GetMapping(value = "/hi")
            String sayHiFromClientOne(@RequestParam(value = "name", defaultValue = "黃世民") 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：

package com.springcloud.servicefeign.controller;

import com.springcloud.servicefeign.feign.SchedualServiceHi;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

/**
 * @PACKAGE_NAME com.springcloud.servicefeign.controller
 * @PROJECT_NAME service-feign
 * @建立人 huang
 * @建立時間 2018/11/27
 */
@RestController
public class HiController {

    @Autowired
    private SchedualServiceHi schedualServiceHi;

    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam("name") String name) {
        return schedualServiceHi.sayHiFromClientOne(name);
    }
}

啟動程式，多次訪問http://localhost:9003/hi?name=hsm,瀏覽器交替顯示

hihsm,i am from port:9000
hihsm,i am from port:8889

4.參考資料
spring-cloud-feign