Spring Cloud服务的注册与发现（Eureka）

一、spring cloud简介

spring cloud 为开发人员提供了快速构建分布式系统的一些工具，包括配置管理、服务发现、断路器、路由、微代理、事件总线、全局锁、决策竞选、分布式会话等等。它运行环境简单，可以在开发人员的电脑上跑。另外说明spring cloud是基于springboot的，所以需要开发中对springboot有一定的了解。另外对于“微服务架构” 不了解的话，可以通过搜索引擎搜索“微服务架构”了解下。

二、创建服务注册中心

在这里，我们需要用的的组件上Spring Cloud Netflix的Eureka ,eureka是一个服务注册和发现模块。

2.1 首先创建一个maven主工程。

**2.2 然后创建2个model工程:**一个model工程作为服务注册中心，即Eureka Server,另一个作为Eureka Client。

下面以创建server为例子，详细说明创建过程：

右键工程->创建model-> 选择spring initialir 如下图：

下一步->选择cloud discovery->eureka server ,然后一直下一步就行了。

创建完后的工程的pom.xml文件如下：

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<?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 [url]http://maven.apache.org/xsd/maven-4.0.0.xsd[/url]">         <modelVersion>4.0.0</modelVersion>           <groupId>com.forezp</groupId>         <artifactId>eurekaserver</artifactId>         <version>0.0.1-SNAPSHOT</version>         <packaging>jar</packaging>           <name>eurekaserver</name>         <description>Demo project for Spring Boot</description>           <parent>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-parent</artifactId>             <version>1.5.2.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>1.8</java.version>         </properties>           <dependencies>             <!--eureka server -->             <dependency>                 <groupId>org.springframework.cloud</groupId>                 <artifactId>spring-cloud-starter-eureka-server</artifactId>             </dependency>               <!-- spring boot test-->             <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>Dalston.RC1</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>[url]https://repo.spring.io/milestone</url>[/url]                 <snapshots>                     <enabled>false</enabled>                 </snapshots>             </repository>         </repositories>         </project>

2.3 启动一个服务注册中心，只需要一个注解@EnableEurekaServer，这个注解需要在springboot工程的启动application类上加：

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@EnableEurekaServer     @SpringBootApplication     public class EurekaserverApplication {           public static void main(String[] args) {             SpringApplication.run(EurekaserverApplication.class, args);         }     }

**2.4 **eureka是一个高可用的组件，它没有后端缓存，每一个实例注册之后需要向注册中心发送心跳（因此可以在内存中完成），在默认情况下erureka server也是一个eureka client ,必须要指定一个 server。eureka server的配置文件application.yml：

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server:       port: 8761       eureka:       instance:         hostname: localhost       client:         registerWithEureka: false         fetchRegistry: false         serviceUrl:           defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

通过eureka.client.registerWithEureka：false和fetchRegistry：false来表明自己是一个eureka server.

2.5 eureka server 是有界面的，启动工程,打开浏览器访问：
http://localhost:8761 ,界面如下：

No application available 没有服务被发现 ……_
因为没有注册服务当然不可能有服务被发现了。

三、创建一个服务提供者 (eureka client)

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 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。

创建过程同server类似,创建完pom.xml如下：

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<?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 [url]http://maven.apache.org/xsd/maven-4.0.0.xsd[/url]">        <modelVersion>4.0.0</modelVersion>          <groupId>com.forezp</groupId>        <artifactId>service-hi</artifactId>        <version>0.0.1-SNAPSHOT</version>        <packaging>jar</packaging>          <name>service-hi</name>        <description>Demo project for Spring Boot</description>          <parent>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-parent</artifactId>            <version>1.5.2.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>1.8</java.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-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>Dalston.RC1</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>[url]https://repo.spring.io/milestone</url>[/url]                <snapshots>                    <enabled>false</enabled>                </snapshots>            </repository>        </repositories>        </project>

通过注解@EnableEurekaClient 表明自己是一个eurekaclient.

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@SpringBootApplication     @EnableEurekaClient     @RestController     public class ServiceHiApplication {           public static void main(String[] args) {             SpringApplication.run(ServiceHiApplication.class, args);         }           @Value("${server.port}")         String port;         @RequestMapping("/hi")         public String home(@RequestParam String name) {             return "hi "+name+",i am from port:" +port;         }       }

仅仅@EnableEurekaClient是不够的，还需要在配置文件中注明自己的服务注册中心的地址，application.yml配置文件如下：

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eureka:       client:         serviceUrl:           defaultZone: http://localhost:8761/eureka/     server:       port: 8762     spring:       application:         name: service-hi

需要指明spring.application.name,这个很重要，这在以后的服务与服务之间相互调用一般都是根据这个name 。
启动工程，打开http://localhost:8761 ，即eureka server 的网址：

你会发现一个服务已经注册在服务中了，服务名为SERVICE-HI ,端口为7862

这时打开 http://localhost:8762/hi?name=forezp ，你会在浏览器上看到 :

hi forezp,i am from port:8762