Spring Cloud構建微服務架構 | 第二篇： 服務消費者（rest+ribbon）

目錄

在上一篇文章，講了服務的註冊和發現。在微服務架構中，業務都會被拆分成一個獨立的服務，服務與服務的通訊是基於http restful的。Spring cloud有兩種服務調用方式，一種是ribbon+restTemplate，另一種是feign。在這一篇文章首先講解下基於ribbon+rest。

一、ribbon簡介

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.
—–摘自官網

ribbon是一個負載均衡客戶端，可以很好的控制htt和tcp的一些行爲。Feign默認集成了ribbon。

下表顯示了Spring Cloud Netflix默認爲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、準備工作

這一篇文章基於上一篇文章的工程，啓動eurekaserver 工程；啓動serviceclient工程，它的端口爲8762；將serviceclient的配置文件的端口改爲8763,並啓動，這時你會發現：serviceclient在eurekaserver註冊了2個實例，這就相當於一個小的集羣。訪問localhost:8761如圖所示：

三、建一個服務消費者

重新新建一個spring-boot工程，取名爲：serviceribbon;
在它的pom.xml文件分別引入起步依賴spring-cloud-starter-netflix-eureka-client、spring-cloud-starter-netflix-ribbon、spring-boot-starter-web，代碼如下：

<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務的註冊中心地址爲http://localhost:8761/eureka/，程序名稱爲 service-ribbon，程序端口爲8764。配置文件application.yml如下：

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
server:
  port: 8764
spring:
  application:
    name: ServiceRibbon

application.properties配置如下：

eureka. client.serviceUrl.defaultZone=http://localhost:8761/eureka/
server.port=8764
spring.application.name=ServiceRibbon

在工程的啓動類中,通過@EnableDiscoveryClient向服務中心註冊；並且向程序的ioc注入一個bean: restTemplate;並通過@LoadBalanced註解表明這個restRemplate開啓負載均衡的功能。

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();
    }

}

寫一個測試類HelloService，通過之前注入ioc容器的restTemplate來消費eurekaclient服務的“/hi”接口，在這裏我們直接用的程序名替代了具體的url地址，在ribbon中它會根據服務名來選擇具體的服務實例，根據服務實例在請求的時候會用具體的url替換掉服務名，代碼如下：

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);
    }

}

寫一個controller，在controller中用調用HelloService 的方法，代碼如下：

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);
    }
}

在瀏覽器上多次訪問http://localhost:8764/hi?name=Eureka，瀏覽器交替顯示：

hi Eureka,i am from port:8762

hi Eureka,i am from port:8763

這說明當我們通過調用restTemplate.getForObject(“http://eurekaclient/hi?name=“+name,String.class)方法時，已經做了負載均衡，訪問了不同的端口的服務實例。