Spring Cloud Feign是一套基於Netflix Feign實現的聲明式服務調用客戶端。它使得編寫Web服務客戶端變得更加簡單。我們只需要通過創建接口並用註解來配置它既可完成對Web服務接口的綁定。它具備可插拔的註解支持，包括Feign註解、JAX-RS註解。它也支持可插拔的編碼器和解碼器。Spring Cloud Feign還擴展了對Spring MVC註解的支持，同時還整合了Ribbon和Eureka來提供均衡負載的HTTP客戶端實現。

1、pom.xml，這裏有所不同dependencyManagement有變化，之前的跑不通，依賴標紅處為修改

<?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>eurekaRibbon</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

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

    <parent>
        <groupId>org.springframework.boot</
 
groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.0.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.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>Dalston.SR3</version> -->
                <version>Camden.SR4</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>

2、主類：通過@EnableFeignClients註解開啟掃描Spring Cloud Feign客戶端的功能

package com.example.demo;

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;

//掃描com.example.demo.service下的FeignClient
@EnableFeignClients(basePackages={"com.example.demo.service"})
@EnableDiscoveryClient
@SpringBootApplication
public class EurekaFeignApplication {

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

3、ClientFeignController

package com.example.demo.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.service.IFeign;

@RestController
public class ClientFeignController {

    @Autowired
    IFeign iFeign;

    @GetMapping("/consumer")
    public String all() {
        // 發起REST請求
        return iFeign.all();
    }
    
}

4、IFeign 一個FeignClient 聲明 服務提供者的信息

package com.example.demo.service;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

//聲明服務提供名
@FeignClient("eurekaClient")
public interface IFeign {

    //指定要消費的接口名稱
//    @GetMapping("/consumer")
    @RequestMapping(value="/all",method={RequestMethod.GET})
    String all();
}

　比上篇使用Ribbon @LoadBalanced，更加具有可配置性

　如果使用Dalston版，FeignClient使用GetMapping 會報java.lang.NoClassDefFoundError: feign/Feign$Builder，網上查了很多 暫時沒有找到原因， 故而 換成Camden版。

Spring Cloud 入門Eureka -Consumer服務消費（聲明式Feign）（三）