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SpringCloud(二):服务发现与消费

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通过上一节内容介绍与实践，我们已经搭建起微服务架构中的核心组件——服务注册中心 SpringCloud(一):服务注册中心Eureka

以下Model基于上一节项目新增

现在我们已经有了一个服务注册中心，下面就来尝试下构建服务提供者和服务消费者，

###注册服务提供者

当client向server注册时，它会提供一些元数据，例如主机和端口，URL，主页等。Eureka server（注册中心）从每个client实例接收心跳消息。如果心跳超时，则通常将该实例从注册server中删除。

创建一个model项目(eureka-client)

服务提供者的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.caogen</groupId>
  	<artifactId>eureka-client</artifactId>
  	<version>0.0.1-SNAPSHOT</version>
  	<packaging>jar</packaging>

  	<name>eureka-client</name>
  	<description>Demo project for Spring Boot</description>

  	<parent>
  		<groupId>org.springframework.boot</groupId>
  		<artifactId>spring-boot-starter-parent</artifactId>
  		<version>1.5.8.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>Edgware.RELEASE</spring-cloud.version>
  	</properties>

  	<dependencies>
  		<dependency>
  			<groupId>org.springframework.cloud</groupId>
  			<artifactId>spring-cloud-starter-eureka</artifactId>
  		</dependency>

  		<dependency>
  			<groupId>org.springframework.boot</groupId>
  			<artifactId>spring-boot-starter-test</artifactId>
  			<scope>test</scope>
  		</dependency>

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

在应用类中通过加上@EnableDiscoveryClient注解，表明自己是服务提供者

import org.springframework.boot.SpringApplication;
  import org.springframework.boot.autoconfigure.SpringBootApplication;
  import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

  @EnableDiscoveryClient
  @SpringBootApplication
  public class EurekaClientApplication {

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

需要在application.yml配置文件中，通过一系列配置来制定注册中心地址和服务名等等

server:
    port: 1112

  management:
    security:
  	enabled: false

  spring:
    application:
  	name: eureka-client

  eureka:
    client:
  	serviceUrl:
  			  defaultZone: http://localhost:1111/eureka/

创建HelloController类并实现/hello接口

import org.springframework.cloud.client.ServiceInstance;
  import org.springframework.cloud.client.discovery.DiscoveryClient;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.bind.annotation.RestController;

  import javax.annotation.Resource;

  @RestController
  public class HelloController {

  	@Resource
  	private DiscoveryClient client;

  	@RequestMapping("/hello")
  	public String sayHello() {
  		ServiceInstance instance = client.getLocalServiceInstance();
  		return "Hello,World! port:" + instance.getPort();
  	}

  }

然后在注册中心启动的情况下，启动eureka-client

SpringCloud(二):服务发现与消费

我们可以通过访问Eureka的信息面板看到服务的注册信息

SpringCloud(二):服务发现与消费

我通过修改端口又启动了一个eureka-client应用，这个时候有两个服务提供实例了。可以看到名为EUREKA-CLIENT的服务中出现了两个实例单元。

###服务消费者

现在我们已经有了服务注册中心和服务提供者，下面就来尝试构建一个服务消费者，它主要完成两个目标，发现服务以及消费服务。其中，服务发现的任务有Eureka的客户端完成，而服务消费的任务由Ribbon完成。Ribbon是一个基于HTTP和TCP的客户端负载均衡器

创建一个Model项目(ribbon-consumer)

服务消费者的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.caogen</groupId>
  	<artifactId>ribbon-consumer</artifactId>
  	<version>0.0.1-SNAPSHOT</version>
  	<packaging>jar</packaging>

  	<name>ribbon-consumer</name>
  	<description>Demo project for Spring Boot</description>

  	<parent>
  		<groupId>org.springframework.boot</groupId>
  		<artifactId>spring-boot-starter-parent</artifactId>
  		<version>1.5.8.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>Edgware.RELEASE</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-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-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>

在应用类中通过@EnableDiscoveryClient注解让该应用注册为Eureka客户端应用，以获得服务发现的能力。同事，在该主类中创建RestTemplate的Spring Bean实例，并通过@LoadBalanced注解开启客户端负载均衡。

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;

  @EnableDiscoveryClient
  @SpringBootApplication
  public class RibbonConsumerApplication {

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

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

创建ConsumerController类并实现/ribbon接口。

import org.springframework.web.bind.annotation.GetMapping;
  import org.springframework.web.bind.annotation.RestController;
  import org.springframework.web.client.RestTemplate;

  import javax.annotation.Resource;

  @RestController
  public class ConsumerController {

  	@Resource
  	RestTemplate restTemplate;

  	@GetMapping(value = "/ribbon")
  	public String helloConsumer() {
  		return restTemplate.getForObject("http://EUREKA-CLIENT/hello", String.class);
  	}

  }

需要在application.yml配置文件中，通过一系列配置来制定注册中心地址和服务名等等

eureka:
    client:
  	serviceUrl:
  	  defaultZone: http://localhost:1111/eureka/

  server:
    port: 1115
  spring:
    application:
  	name: ribbon-consumer