Spring Cloud Alibaba之Nacos-服务消费者(Feign)

一、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

二、POM

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

<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>4.0.0modelVersion>

    <parent>
        <groupId>com.funtlgroupId>
        <artifactId>hello-spring-cloud-alibaba-dependenciesartifactId>
        <version>1.0.0-SNAPSHOTversion>
        <relativePath>../hello-spring-cloud-alibaba-dependencies/pom.xmlrelativePath>
    parent>

    <artifactId>hello-spring-cloud-alibaba-nacos-consumer-feignartifactId>
    <packaging>jarpackaging>

    <name>hello-spring-cloud-alibaba-nacos-consumer-feignname>
    <url>http://www.funtl.comurl>
    <inceptionYear>2018-NowinceptionYear>

    <dependencies>
        
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-actuatorartifactId>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
            <scope>testscope>
        dependency>
        

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discoveryartifactId>
        dependency>
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-openfeignartifactId>
        dependency>
        
    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
                <configuration>
                    <mainClass>com.funtl.hello.spring.cloud.alibaba.nacos.consumer.feign.NacosConsumerFeignApplicationmainClass>
                configuration>
            plugin>
        plugins>
    build>
project>

主要增加了 org.springframework.cloud:spring-cloud-starter-openfeign 依赖

三、Application

通过 @EnableFeignClients 注解开启 Feign 功能

package com.funtl.hello.spring.cloud.alibaba.nacos.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);
    }
}

四、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.funtl.hello.spring.cloud.alibaba.nacos.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 EchoService {

    @GetMapping(value = "/echo/{message}")
    String echo(@PathVariable("message") String message);
}

五、Controller

package com.funtl.hello.spring.cloud.alibaba.nacos.consumer.feign.controller;

import com.funtl.hello.spring.cloud.alibaba.nacos.consumer.feign.service.EchoService;
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 EchoService echoService;

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

六、application.yml

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

server:
  port: 9092

management:
  endpoints:
    web:
      exposure:
        include: "*"

七、启动工程

通过浏览器访问 http://localhost:8848/nacos，即 Nacos Server 网址

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你会发现多了一个名为 nacos-consumer-feign 的服务

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

Hello Nacos Discovery Hi Feign

八、测试负载均衡

• 启动多个 consumer-provider 实例，效果图如下：

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• 修改 consumer-provider 项目中的 Controller 代码，用于确定负载均衡生效

package com.funtl.hello.spring.cloud.alibaba.nacos.provider;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@EnableDiscoveryClient
public class NacosProviderApplication {
    public static void main(String[] args) {
        SpringApplication.run(NacosProviderApplication.class, args);
    }

    @Value("${server.port}")
    private String port;

    @RestController
    public class EchoController {
        @GetMapping(value = "/echo/{message}")
        public String echo(@PathVariable String message) {
            return "Hello Nacos Discovery " + message + " i am from port " + port;
        }
    }
}

• 在浏览器上多次访问 http://localhost:9092/echo/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

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