Eureka之服务发现

本文介绍微服务作为Eureka Client如何从Eureka Server发现/拉取服务。

1 创建项目，导入依赖

<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.yiidian</groupId>
	<artifactId>user_consumer</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.1.RELEASE</version>
		<relativePath />
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
		<!-- SpringCloud版本，F系列 -->
		<spring-cloud.version>Finchley.RC1</spring-cloud.version>
	</properties>

	<dependencies>
		<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>
		<!-- 添加OkHttp支持 -->
		<dependency>
			<groupId>com.squareup.okhttp3</groupId>
			<artifactId>okhttp</artifactId>
			<version>3.9.0</version>
		</dependency>
		<!-- Eureka客户端 -->
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
		</dependency>
	</dependencies>
	
	<dependencyManagement>
		<dependencies>
			<!-- SpringCloud依赖，一定要放到dependencyManagement中，起到管理版本的作用即可 -->
			<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>

	<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>

2 配置Eureka Client

建立application.yml，内容如下：

  # Eureka服务拉取配置
eureka:
  client:
    register-with-eureka: false  
    fetch-registry: true  # 服务消费方必须从Eureka服务器拉取注册信息，该值必须为true
    service-url:
      defaultZone: http://127.0.0.1:10086/eureka  

3 编写启动类

package com.yiidian;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
/**
 * 一点教程网 - http://www.yiidian.com
 *
 */
@SpringBootApplication
@EnableEurekaClient // 开启Eureka客户端
public class UserConsumerApplication {

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

}

4 使用RestTemplate拉取服务

1）在启动类实例化RestTemplate对象

package com.yiidian;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
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.RestTemplate;

/**
 * 一点教程网 - http://www.yiidian.com
 *
 */
@SpringBootApplication
@EnableEurekaClient // 开启Eureka客户端
public class UserConsumerApplication {

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

	/**
	 * 创建RestTemplate
	 */
	@Bean // 把RestTemplate放入IOC容器
	public RestTemplate createRestTemplate() {
		return new RestTemplate();
	}
}

2）编写代码获取Eureka服务

@Autowired
private DiscoveryClient discoveryClient;

/**
 * 使用RestTemplate从Eureka Server获取服务
 */
@RequestMapping("/{id}")
public User findById(@PathVariable("id")Integer id) {
	//1.从Eureka获取服务ID
	List<ServiceInstance> instances = discoveryClient.getInstances("user-service");
	//2.获取第一个即可
	ServiceInstance serviceInstance = instances.get(0);
	
	String url = "http://"+serviceInstance.getHost()+":"+serviceInstance.getPort()+"/user/"+id;
	
	System.out.println(url);
	
	User user = restTemplate.getForObject(url, User.class);
	
	return user;
}