Ribbon（负载均衡的客户端）

前面讲了服务的注册与发现，微服务项目会把项目的各个业务需求划分成几个模块来单独提供服务，各服务间的调用都是采用Http Restful来实现，但是在SpringClound中服务间的调用有两种方式：一种是ribbon+ restTemplate;另一种是feign;

 Ribbon：在SpringClound中是作为一个负载均衡的客户端，控制访问入口，定制访问策略等功能; Feign组件同时也是集成了ribbon的

打开前面准备的服务client

在Idea里，新建项目，选择Spring initializer.

勾选组件

下面的pom

<?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.example</groupId>
	<artifactId>spring-clound-ribbon-example</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>spring-clound-ribbon-example</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.0.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>Greenwich.M3</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
			<version>1.4.4.RELEASE</version>
		</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>

　　

配置properties文件参数;

#服务端口
server.port=8885
#注册服务中心地址
eureka.client.service-url.defaultZone=http://localhost:8882/eureka/
#注册服务端name
spring.application.name=service-ribbon
#调用连接时间
eureka.client.eureka-server-read-timeout-seconds=6000
#调用连接时间
eureka.client.eureka-server-connect-timeout-seconds=6000
hystrix.metrics.polling-interval-ms=6000

　　

在启动类上添加注解@EnableDiscoveryClient

@EnableDiscoveryClient
@SpringBootApplication
public class SpringCloundRibbonExampleApplication {

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

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

　　

创建conroller、service

@RestController
public class HelloController {

    @Autowired
    IHelloService helloService;

    @RequestMapping(value = "/index")
    public String index() {
        return helloService.index();
    }

}

　　

@Service
public class HelloServiceImpl implements IHelloService {

    @Autowired
    RestTemplate restTemplate;

    @Override
    public String index() {
        return restTemplate.getForObject("http://SERVICE-HELLO/index",String.class);
    }
}

　　

启动项目，然后再看服务中心，已经注册成功

回到浏览器，输入http://localhost:8885/index

刷新：