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有兩種服務呼叫方式，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的一些行為。Feign預設集成了ribbon。

ribbon 已經預設實現了這些配置bean：

• IClientConfig ribbonClientConfig: DefaultClientConfigImpl

• IRule ribbonRule: ZoneAvoidanceRule

• IPing ribbonPing: NoOpPing

• ServerList ribbonServerList: ConfigurationBasedServerList

• ServerListFilter ribbonServerListFilter: ZonePreferenceServerListFilter

• ILoadBalancer ribbonLoadBalancer: ZoneAwareLoadBalancer

二、開發流程

pom.xml

<?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.gui</groupId>
   <artifactId>springribbon</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>

   <name>springribbon</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>2.0.2.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>9</java.version>
      <spring-cloud.version>Finchley.BUILD-SNAPSHOT</spring-cloud.version>
   </properties>

   <dependencies>



      <!--pom.xml檔案分別引入起步依賴spring-cloud-starter-netflix-eureka-client、spring-cloud-starter-ribbon、spring-boot-starter-web-->

      <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-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-snapshots</id>
         <name>Spring Snapshots</name>
         <url>https://repo.spring.io/snapshot</url>
         <snapshots>
            <enabled>true</enabled>
         </snapshots>
      </repository>
      <repository>
         <id>spring-milestones</id>
         <name>Spring Milestones</name>
         <url>https://repo.spring.io/milestone</url>
         <snapshots>
            <enabled>false</enabled>
         </snapshots>
      </repository>
   </repositories>


</project>

package com.gui.springribbon;

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 SpringribbonApplication {

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

   @Bean
   @LoadBalanced
   RestTemplate restTemplate() {
      return new RestTemplate();
   }

}

application.yml

server:
  port: 8764


eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/



spring:
  application:
    name: service-ribbon

package com.gui.springribbon.web;

import com.gui.springribbon.service.HelloService;
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 HelloControler {

    @Autowired
    HelloService helloService;
    @RequestMapping(value = "/hi")
    public String hi(@RequestParam String name){
        return helloService.hiService(name);
    }


}

service

package com.gui.springribbon.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://SERVICE-HI/hi?name="+name,String.class);
    }

}