springCloud-netflix-Eureka服务消费者(Feign)

上一篇文章，讲述了如何通过RestTemplate+Ribbon去消费服务，这篇文章主要讲述如何通过Feign去消费服务。

1.Feign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，并和Eureka结合，默认实现了负载均衡的效果。

简而言之：

Feign 采用的是基于接口的注解
Feign 整合了ribbon

2.准备工作
继续用上一节的工程，启动netflix-eureka-server，端口为8888; 启动netflix-eureka-provider两次，端口分别为8889、9000.
3.创建一个feign的服务

新建一个spring-boot工程，取名为serice-feign，在它的pom文件引入Feign的起步依赖spring-cloud-starter-feign、Eureka的起步依赖spring-cloud-starter-eureka、Web的起步依赖spring-boot-starter-web，代码如下：

<?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>

在工程的配置文件application.yml文件，指定程序名为service-feign-consumer，端口号为9003，服务注册地址为http://localhost:8888/eureka/ ，代码如下

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

server:
  port: 9003

spring:
  application:
    name: service-feign-consumer

在程序的启动类ServiceFeignApplication上加，@EnableDiscoveryClient //向服务中心注册;并且向程序ioc注入一个bean和@EnableFeignClients //开启feign的功能的注解

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 //向服务中心注册;并且向程序ioc注入一个bean
@EnableFeignClients //开启feign的功能
public class ServiceFeignApplication {

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

定义一个feign接口，通过@ FeignClient（“服务名”），来指定调用哪个服务。比如在代码中调用了service-cart服务的“/hi”接口，代码如下：

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
 * @创建人 huang
 * @创建时间 2018/11/27
 */
@FeignClient(value = "service-cart")
public interface SchedualServiceHi {

    /**
     * 定义一个feign接口，通过@ FeignClient（“服务名”），来指定调用哪个服务。
     * 比如在代码中调用了service-cart服务的“/hi”接口
     */
    @GetMapping(value = "/hi")
            String sayHiFromClientOne(@RequestParam(value = "name", defaultValue = "黄世民") String name);

}

在Web层的controller层，对外暴露一个”/hi”的API接口，通过上面定义的Feign客户端SchedualServiceHi 来消费服务。代码如下：

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
 * @创建人 huang
 * @创建时间 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);
    }
}

在这里插入图片描述
启动程序，多次访问http://localhost:9003/hi?name=hsm,浏览器交替显示

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

4.参考资料
spring-cloud-feign

springCloud-netflix-Eureka服务消费者(Feign)

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