ribbon

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http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**
	
	启动eureka-server 工程；启动service-provider工程，它的端口为9091；
	将service-provider的配置文件的端口改为9092,并启动，这时你会发现：service-provider在eureka-server注册了2个实例，这就相当于一个小的集群。访问localhost:9090如图所示：

![集群01](集群01.png)

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：

```
<?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>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.19.RELEASE</version>
		<relativePath/> 
	</parent>
	<groupId>com.jeffrey</groupId>
	<artifactId>jc_service_ribbon</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>jc_service_ribbon</name>
	<description>Demo project for Spring Boot</description>

<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Edgware.SR5</spring-cloud.version>
	</properties>

<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<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-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>

</project>

```

在工程的配置文件指定服务的注册中心地址为http://localhost:10001/eureka/，程序名称为 service-ribbon，程序端口为10004。配置文件application.yml如下：

```

server:
  port: 10004

spring:
  application:
    name: service-ribbon
eureka:
  client:
    service-url:
      defaultZone: http://localhost:10001/eureka/
```

```
package com.jeffrey;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestOperations;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableDiscoveryClient   //服务发现者（消费者）
public class JcServiceRibbonApplication {

public static void main(String[] args) {
		SpringApplication.run(JcServiceRibbonApplication.class, args);
	}
//	@Bean
//	@LoadBalanced
//	public RestTemplate getRestTemplate(){
//		return  new RestTemplate();
//	}
	@Bean
	@LoadBalanced
	RestOperations restTemplate(RestTemplateBuilder builder) {
		return builder.build();
	}
}

```

业务类实现：

```
package com.jeffrey.service.impl;

import com.jeffrey.service.DeptService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestOperations;
import org.springframework.web.client.RestTemplate;

/**
 * Created by jeffrey on 2019/3/29.
 */
@Service
public class DeptServiceImpl  implements DeptService{
    @Autowired
    RestOperations restTemplate;
    public String fetchInfo(String id) {

return restTemplate.getForObject("http://SERVICE-PROVIDER/dept?id="+id,String.class);
    }
}

```