概述 

Feign 是一个声明式的伪 Http 客户端,它使得写 Http 客户端变得更简单。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,Nacos 也很好的兼容了 Feign,默认实现了负载均衡的效果

  • Feign 采用的是基于接口的注解
  • Feign 整合了 ribbon

3.1 创建服务消费者

3.1.1 创建一个工程名为 hello-spring-cloud-alibaba-nacos-consumer 的服务消费者项目,pom.xml 配置如下:

<?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>
    <parent>
        <groupId>com.wsl</groupId>
        <artifactId>hello-spring-cloud-alibaba-dependencies</artifactId>
        <version>1.0.0-SNAPSHOT</version>
        <relativePath>../hello-spring-cloud-alibaba-dependencies/pom.xml</relativePath>
    </parent>
    <artifactId>hello-spring-cloud-alibaba-consumer</artifactId>
    <packaging>jar</packaging>

    <name>hello-spring-cloud-alibaba-consumer</name>
    <description>Demo project for Spring Cloud Alibaba</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!-- Spring Boot Begin -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>
        <!-- Spring Boot End -->

        <!-- Spring Cloud Begin -->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-loadbalancer</artifactId>
        </dependency>
        <!-- Spring Cloud End -->
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <mainClass>com.wsl.consumer.ConsumerFeignApplication</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

3.1.2 Application

通过 @EnableFeignClients 注解开启 Feign 功能

package com.wsl.hello.consumer.feign;

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

3.1.3 创建 Feign 接口

通过 @FeignClient("服务名") 注解来指定调用哪个服务。代码如下:

package com.wsl.hello.consumer.feign.service;

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

@FeignClient(value = "nacos-provider")
public interface FeignService {
    @GetMapping(value = "/test/{message}")
    String test(@PathVariable("message") String message);
}

3.1.4 Controller

package com.wsl.hello.provider.controller;

import com.huitu.iot.service.FeignService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class NacosConsumerFeignController {

    @Autowired
    private FeignService feignService;

    @GetMapping(value = "/test/hi")
    public String test() {
        return feignService.test("Hi Feign");
    }
}

3.1.5 application.yml

spring:
  application:
    name: nacos-consumer
  cloud:
    nacos:
      discovery:
        server-addr: 127.0.0.1:8848

server:
  port: 9092

management:
  endpoints:
    web:
      exposure:
        include: "*"
feign:
  sentinel:
    enabled: true

3.2 启动工程

通过浏览器访问 http://localhost:8848/nacos, 即 Nacos Server 网址
你会发现多了一个名为 nacos-consumer 的服务

这时打开 http://localhost:9092/test/hi ,你会在浏览器上看到:

Hello Nacos Discovery Hi Feign i am from port 8081

3.2.1 测试负载均衡

idea启动多个实例
15087669-8c79b9ef2b1677a6

然后修改yml文件里的端口号再启动一个就可以了。
在浏览器上多次访问 http://localhost:9092/test/hi, 浏览器交替显示:

Hello Nacos Discovery Hi Feign i am from port 8081
Hello Nacos Discovery Hi Feign i am from port 8082

参考链接:Spring Cloud Alibaba系列教程

Q.E.D.