Spring Cloud服务消费者（rest+ribbon）

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。

ribbon 已经默认实现了这些配置bean：

• IClientConfig ribbonClientConfig: DefaultClientConfigImpl
• IRule ribbonRule: ZoneAvoidanceRule
• IPing ribbonPing: NoOpPing
• ServerList ribbonServerList: ConfigurationBasedServerList
• ServerListFilter ribbonServerListFilter: ZonePreferenceServerListFilter
• ILoadBalancer ribbonLoadBalancer: ZoneAwareLoadBalancer

二、准备工作

这一篇文章基于上一篇文章的工程，启动eureka-server 工程；启动service-hi工程，它的端口为8762；将service-hi的配置文件的端口改为8763,并启动，这时你会发现：service-hi在eureka-server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：

如何一个工程启动多个实例，请看这篇文章:https://blog.csdn.net/forezp/article/details/76408139

三、建一个服务消费者

重新新建一个spring-boot工程，取名为：service-ribbon;
在它的pom.xml文件分别引入起步依赖spring-cloud-starter-eureka、spring-cloud-starter-ribbon、spring-boot-starter-web，代码如下：

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<?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 [url]http://maven.apache.org/xsd/maven-4.0.0.xsd[/url]">        <modelVersion>4.0.0</modelVersion>          <groupId>com.forezp</groupId>        <artifactId>service-ribbon</artifactId>        <version>0.0.1-SNAPSHOT</version>        <packaging>jar</packaging>          <name>service-ribbon</name>        <description>Demo project for Spring Boot</description>          <parent>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-parent</artifactId>            <version>1.5.2.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.cloud</groupId>                <artifactId>spring-cloud-starter-eureka</artifactId>            </dependency>            <dependency>                <groupId>org.springframework.cloud</groupId>                <artifactId>spring-cloud-starter-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>Dalston.RC1</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>[url]https://repo.spring.io/milestone</url>[/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：

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eureka:       client:         serviceUrl:           defaultZone: http://localhost:8761/eureka/     server:       port: 8764     spring:       application:         name: service-ribbon

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。

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@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service-hi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：

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@Service     public class HelloService {           @Autowired         RestTemplate restTemplate;           public String hiService(String name) {             return restTemplate.getForObject("http://SERVICE-HI/hi?name="+name,String.class);         }       }

写一个controller，在controller中用调用HelloService 的方法，代码如下：

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@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=forezp，浏览器交替显示：

hi forezp,i am from port:8762

hi forezp,i am from port:8763

这说明当我们通过调用restTemplate.getForObject(“http://SERVICE-HI/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。

四、此时的架构

• 一个服务注册中心，eureka server,端口为8761
• service-hi工程跑了两个实例，端口分别为8762,8763，分别向服务注册中心注册
• sercvice-ribbon端口为8764,向服务注册中心注册
• 当sercvice-ribbon通过restTemplate调用service-hi的hi接口时，因为用ribbon进行了负载均衡，会轮流的调用service-hi：8762和8763 两个端口的hi接口；
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