目录
在上一篇文章，讲了服务的注册和发现。在微服务架构中，业务都会被拆分成一个独立的服务，服务与服务的通讯是基于http restful的。Spring cloud有两种服务调用方式，一种是ribbon+restTemplate，另一种是feign。在这一篇文章首先讲解下基于ribbon+rest。
一、ribbon简介
Ribbon is a client side load balancer which gives you a lot of control over the behaviour of HTTP and TCP clients. Feign already uses Ribbon, so if you are using @FeignClient then this section also applies.
—–摘自官网
ribbon是一个负载均衡客户端，可以很好的控制htt和tcp的一些行为。Feign默认集成了ribbon。
下表显示了Spring Cloud Netflix默认为Ribbon提供的bean：
| Bean Type | Bean Name | Class Name |
|---|---|---|
| IClientConfig | ribbonClientConfig | DefaultClientConfigImpl |
| IRule | ribbonRule | ZoneAvoidanceRule |
| IPing | ribbonPing | DummyPing |
| ServerList< server > | ribbonServerList | ConfigurationBasedServerList |
| ServerListFilter< Server > | ribbonServerListFilter | ZonePreferenceServerListFilter |
| ILoadBalancer | ribbonLoadBalancer | ZoneAwareLoadBalancer |
| ServerListUpdater | ribbonServerListUpdater | PollingServerListUpdater |
二、准备工作
这一篇文章基于上一篇文章的工程，启动eurekaserver 工程；启动serviceclient工程，它的端口为8762；将serviceclient的配置文件的端口改为8763,并启动，这时你会发现：serviceclient在eurekaserver注册了2个实例，这就相当于一个小的集群。访问localhost:8761如图所示：
三、建一个服务消费者
重新新建一个spring-boot工程，取名为：serviceribbon;
在它的pom.xml文件分别引入起步依赖spring-cloud-starter-netflix-eureka-client、spring-cloud-starter-netflix-ribbon、spring-boot-starter-web，代码如下：
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.springcloud</groupId>
<artifactId>ServiceRibbon</artifactId>
<packaging>war</packaging>
<version>0.0.1-SNAPSHOT</version>
<name>ServiceRibbon</name>
<description>Demo project for Spring cloud ribbon</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.4.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>
<spring-cloud.version>Finchley.SR1</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-ribbon</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>${spring-cloud.version}</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>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
</project>在工程的配置文件指定服务的注册中心地址为http://localhost:8761/eureka/，程序名称为 service-ribbon，程序端口为8764。配置文件application.yml如下：
eureka:
client:
serviceUrl:
defaultZone: http://localhost:8761/eureka/
server:
port: 8764
spring:
application:
name: ServiceRibbonapplication.properties配置如下：
eureka. client.serviceUrl.defaultZone=http://localhost:8761/eureka/
server.port=8764
spring.application.name=ServiceRibbon在工程的启动类中,通过@EnableDiscoveryClient向服务中心注册；并且向程序的ioc注入一个bean: restTemplate;并通过@LoadBalanced注解表明这个restRemplate开启负载均衡的功能。
package com.springcloud.eurekaribbon;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
@EnableDiscoveryClient
public class ServiceRibbonApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceRibbonApplication.class, args);
}
@Bean
@LoadBalanced
RestTemplate restTemplate() {
return new RestTemplate();
}
}
写一个测试类HelloService，通过之前注入ioc容器的restTemplate来消费eurekaclient服务的“/hi”接口，在这里我们直接用的程序名替代了具体的url地址，在ribbon中它会根据服务名来选择具体的服务实例，根据服务实例在请求的时候会用具体的url替换掉服务名，代码如下：
package com.springcloud.eurekaribbon.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
@Service
public class HelloService {
@Autowired
RestTemplate restTemplate;
public String hiService(String name) {
return restTemplate.getForObject("http://eurekaclient/hi?name="+name,String.class);
}
}写一个controller，在controller中用调用HelloService 的方法，代码如下：
package com.springcloud.eurekaribbon.controller;
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;
import com.springcloud.eurekaribbon.service.HelloService;
@RestController
public class HelloControler {
@Autowired
HelloService helloService;
@RequestMapping(value = "/hi")
public String hi(@RequestParam String name){
return helloService.hiService(name);
}
}在浏览器上多次访问http://localhost:8764/hi?name=Eureka，浏览器交替显示：
hi Eureka,i am from port:8762
hi Eureka,i am from port:8763
这说明当我们通过调用restTemplate.getForObject(“http://eurekaclient/hi?name=“+name,String.class)方法时，已经做了负载均衡，访问了不同的端口的服务实例。