微服务SpringCloud之服务调用与负载均衡

上一篇我们学习了服务的注册与发现，本篇博客是在上一篇的基础上学习服务的调用。上一博客主要创建了Eureka的服务端和一个Client，该Client包含了一个Controller用来提供对外服务供外部调用，可以作为生产者。

一、引入依赖

前面创建了EurekaClient的项目，在项目中引入了spring-cloud-starter-netflix-eureka-client用来注册服务，是生产者，这里调用属于消费者，同样也需要引入spring-cloud-starter-netflix-eureka-client，这里还使用了openfeign来调用生产者提供的服务。具体pom.xml如下，主要引入spring-cloud-starter-netflix-eureka-client、spring-boot-starter-web、spring-cloud-starter-openfeign、spring-cloud-openfeign-core。

<?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>4.0.0modelVersion>
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.1.6.RELEASEversion>
        <relativePath/>
    parent>
    <groupId>com.examplegroupId>
    <artifactId>EurekaConsumerartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>EurekaConsumername>
    <description>Demo project for Spring Bootdescription>
<span>&lt;</span><span>properties</span><span>&gt;</span>
    <span>&lt;</span><span>java.version</span><span>&gt;</span>1.8<span><span>java.version</span><span>&gt;</span>
    <span>&lt;</span><span>spring-cloud.version</span><span>&gt;</span>Greenwich.SR1<span><span>spring-cloud.version</span><span>&gt;</span>
<span><span>properties</span><span>&gt;</span>

<span>&lt;</span><span>dependencies</span><span>&gt;</span>
    <span>&lt;</span><span>dependency</span><span>&gt;</span>
        <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.boot<span><span>groupId</span><span>&gt;</span>
        <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-boot-starter-web<span><span>artifactId</span><span>&gt;</span>
    <span><span>dependency</span><span>&gt;</span>
    <span>&lt;</span><span>dependency</span><span>&gt;</span>
        <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.cloud<span><span>groupId</span><span>&gt;</span>
        <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-cloud-starter-netflix-eureka-client<span><span>artifactId</span><span>&gt;</span>
    <span><span>dependency</span><span>&gt;</span>
    <span>&lt;</span><span>dependency</span><span>&gt;</span>
        <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.cloud<span><span>groupId</span><span>&gt;</span>
        <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-cloud-starter-openfeign<span><span>artifactId</span><span>&gt;</span>
    <span><span>dependency</span><span>&gt;</span>

    <span>&lt;</span><span>dependency</span><span>&gt;</span>
        <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.cloud<span><span>groupId</span><span>&gt;</span>
        <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-cloud-openfeign-core<span><span>artifactId</span><span>&gt;</span>
        <span>&lt;</span><span>version</span><span>&gt;</span>2.1.2.RELEASE<span><span>version</span><span>&gt;</span>
    <span><span>dependency</span><span>&gt;</span>

    <span>&lt;</span><span>dependency</span><span>&gt;</span>
        <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.boot<span><span>groupId</span><span>&gt;</span>
        <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-boot-starter-test<span><span>artifactId</span><span>&gt;</span>
        <span>&lt;</span><span>scope</span><span>&gt;</span>test<span><span>scope</span><span>&gt;</span>
    <span><span>dependency</span><span>&gt;</span>
<span><span>dependencies</span><span>&gt;</span>

<span>&lt;</span><span>dependencyManagement</span><span>&gt;</span>
    <span>&lt;</span><span>dependencies</span><span>&gt;</span>
        <span>&lt;</span><span>dependency</span><span>&gt;</span>
            <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.cloud<span><span>groupId</span><span>&gt;</span>
            <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-cloud-dependencies<span><span>artifactId</span><span>&gt;</span>
            <span>&lt;</span><span>version</span><span>&gt;</span>${spring-cloud.version}<span><span>version</span><span>&gt;</span>
            <span>&lt;</span><span>type</span><span>&gt;</span>pom<span><span>type</span><span>&gt;</span>
            <span>&lt;</span><span>scope</span><span>&gt;</span>import<span><span>scope</span><span>&gt;</span>
        <span><span>dependency</span><span>&gt;</span>
    <span><span>dependencies</span><span>&gt;</span>
<span><span>dependencyManagement</span><span>&gt;</span>

<span>&lt;</span><span>build</span><span>&gt;</span>
    <span>&lt;</span><span>plugins</span><span>&gt;</span>
        <span>&lt;</span><span>plugin</span><span>&gt;</span>
            <span>&lt;</span><span>groupId</span><span>&gt;</span>org.springframework.boot<span><span>groupId</span><span>&gt;</span>
            <span>&lt;</span><span>artifactId</span><span>&gt;</span>spring-boot-maven-plugin<span><span>artifactId</span><span>&gt;</span>
        <span><span>plugin</span><span>&gt;</span>
    <span><span>plugins</span><span>&gt;</span>
<span><span>build</span><span>&gt;</span>

<span>&lt;</span><span>packaging</span><span>&gt;</span>war<span><span>packaging</span><span>&gt;</span>

project>View Code
二、在main类中引入@EnableDiscoveryClient、@EnableFeignClients注解

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.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class EurekaConsumerApplication {

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

}

View Code
@EnableDiscoveryClient :启用服务注册与发现
@EnableFeignClients：启用feign进行远程调用
Feign是一个声明式Web Service客户端。使用Feign能让编写Web Service客户端更加简单, 它的使用方法是定义一个接口，然后在上面添加注解，同时也支持JAX-RS标准的注解。Feign也支持可拔插式的编码器和解码器。Spring Cloud对Feign进行了封装，使其支持了Spring MVC标准注解和HttpMessageConverters。Feign可以与Eureka和Ribbon组合使用以支持负载均衡。
三、配置文件
spring.application.name=spring-cloud-consumer
server.port=9001
eureka.client.serviceUrl.defaultZone=http://localhost:8088/eureka/

四、feign调用实现
package com.example.demo;

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

@FeignClient(name= "spring-cloud-producer")
public interface HelloRemote {

    @RequestMapping(value = "/hello")
    public String hello(@RequestParam(value = "name") String name);

}

name:远程服务名，及spring.application.name配置的名称，此类中的方法和远程服务中contoller中的方法名和参数需保持一致。
五、web层调用远程服务
这里使用@Autowired将远程访问类注入到Controller中用来调用服务。
package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ConsumerController {
    @Autowired
    HelloRemote HelloRemote;

    @RequestMapping("/hello")
    public String index(@RequestParam String name) {
        return HelloRemote.hello(name);
    }
}

六、测试
分别启动Server、Client、Consumer，依次输入http://localhost:8088/、http://localhost:9000/hello?name=cuiyw、http://localhost:9001/hello?name=cuiyw。端口8088是Eureka Server端，9000是Eureka Client，作为生产者，端口9001也是Eureka Client，作为消费者，在端口9001中消费者调用生产者9000提供的服务。



七、负载均衡
修改EurekaClient项目中的Controller和配置文件。在Controller中的index方法增加了修改了return的值，用来区分生产者。在application.properties中修改了端口号。
package com.example.demo;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String index(@RequestParam String name) {
        return "hello "+name+"，this is first messge 2";
    }
}

spring.application.name=spring-cloud-producer
server.port=9002
eureka.client.serviceUrl.defaultZone=http://localhost:8088/eureka/

启动该Client，这时在Eureka Server中可以看到两个生产者。

在浏览器中数次刷新url:http://localhost:9001/hello?name=cuiyw,可以看到不同的响应结果。


八、小结
本篇主要学习了下服务的调用以及简单的使用openfeign进行的负载均衡，后面会参考纯洁的微笑的博文学习熔断器Hystrix。
本篇博客参考:http://www.ityouknow.com/springcloud/2017/05/12/eureka-provider-constomer.html
九、号外
本人的新书已出版上架，书名Spring快速入门，天猫、京东也都能搜得到，这里也算是王婆卖瓜自卖自夸一下，大家如果感兴趣可以了解一下，个人感觉对初学者来说还是值得一读的。


Original: https://www.cnblogs.com/5ishare/p/11147345.html
Author: 社会主义接班人
Title: 微服务SpringCloud之服务调用与负载均衡