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从Eureka server获取服务列表
- Spring cloud环境中的应用，如果注册到Eureka server，就会从Eureka server获取所有应用的注册信息（也叫服务列表），然后保存到本地，这个操作是周期性的，默认每三十秒一次；
- 以下是来自官方的架构图，可以看到Application Service向Eureka Server有Get Registry的请求：
参考文章
- 如果您有兴趣，想深入了解spring广播机制或者Eureka client更新服务列表，推荐您参考以下两篇文章：
- 《spring4.1.8扩展实战之三：广播与监听 》
- 《Spring Cloud源码分析之Eureka篇第五章：更新服务列表 》
实战内容
- 启动Eureka server；
- 开发一个应用springcloudcustomizelistener，启动后会注册到Eureka server；
- 此时该应用身份为Eureka client，会周期性的从Eureka server获取服务列表（已有逻辑）；
- 每次成功获取的服务列表成功都会存入本地缓存（已有逻辑）；
- 存入缓存后，会在spring容器内发送广播（已有逻辑）；
- 本次实战的重点就是自定义一个监听器来接收上述广播，收到广播后把详情用日志打印出来；
- 再启动另一个应用springclouddeepprovider，也会注册到Eureka server；
- 再去观察springcloudcustomizelistener的广播监听日志，会发现springclouddeepprovider的注册信息；
Eureka client缓存服务列表的源码简介
- 实战前，先对Eureka client缓存服务列表的实现源码做个简介，这样才能做出匹配的监听器；
- 应用作为Eureka Client的启动时，在com.netflix.discovery.DiscoveryClient类的initScheduledTasks方法中，会启动周期性任务，每隔30秒从Eureka server获取服务列表信息，如下图，红框中的TimedSupervisorTask负责周期性执行，绿框中的CacheRefreshThread负责具体的更新逻辑：
- 在CacheRefreshThread类中经过层层调用，获取服务列表并更新本地缓存的逻辑在fetchRegistry方法中实现，如下图，红框中的getAndStoreFullRegistry方法负责全量更新，绿框中的getAndUpdateDelta方法负责增量更新，黄框中的onCacheRefreshed方法就是今天的重点：发送广播，广播类型是服务列表的本地缓存已更新
- onCacheRefreshed方法在子类CloudEurekaClient中被重写，可见这里发送了一个普通的spring容器内广播，类型是HeartbeatEvent，我们可以自定义监听类来接收广播，并通过泛型规定只接受HeartbeatEvent类型：
@Override
protected void onCacheRefreshed() {
if (this.cacheRefreshedCount != null) { //might be called during construction and will be null
long newCount = this.cacheRefreshedCount.incrementAndGet();
log.trace("onCacheRefreshed called with count: " + newCount);
//spring容器内广播，HeartbeatEvent实例在创建时收到两个参数：CloudEurekaClient实例和缓存刷新次数
this.publisher.publishEvent(new HeartbeatEvent(this, newCount));
}
}
实战应用设定
- 本次实战要搭建一个小的Spring Cloud环境，包括以下应用：
| 应用名称 |
身份 |
作用 |
端口 |
启动顺序 |
| springclouddeepeureka |
Eureka server |
注册中心 |
8081 |
第一 |
| springcloudcustomizelistener |
Eureka client |
有自定义广播监听器，监听服务列表缓存更新的广播 |
8085 |
第二 |
| springclouddeepprovider |
Eureka client |
普通web应用 |
8082 |
第三 |
源码下载
- springclouddeepeureka和springclouddeepprovider这两个应用，在文章《Spring Cloud源码分析之Eureka篇第一章：准备工作》中已有详细介绍，本文中就不多说了，您可以参考文章，也可以在github下载这两个应用的源码，地址和链接信息如下表所示：
- 这个git项目中有多个文件夹，本章源码分别在springclouddeepeureka、springclouddeepprovider这两个文件夹下，如下图红框所示：
启动springclouddeepeureka
- 应用springclouddeepeureka开发完成后就立即启动，在浏览器访问地址：http://localhost:8081，可见Eureka server已经启动，不过还没有任何应用注册上来，如下图：
开发springcloudcustomizelistener
- 接下来一起开发应用springcloudcustomizelistener，在此应用中添加自定义的spring广播监听器，如果您不想敲代码，也可以从github上直接下载源码，地址和链接信息如下表所示：
- 这个git项目中有多个文件夹，本章源码在springcloudcustomizelistener文件夹下，如下图红框所示：
- 一起来开发吧：
- 创建一个springboot的web应用，pom.xml内容如下，注意为了在日志中展示更详细的内容，依赖了fastjson库：
<?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.bolingcavalry</groupId>
<artifactId>springcloudcustomizelistener</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>springcloudcustomizelistener</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.9.RELEASE</version>
</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.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>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.28</version>
</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>Edgware.RELEASE</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>
- 应用配置文件application.yml的内容如下：
server:
port: 8085
spring:
application:
name: springcloud-customize-listener
eureka:
client:
serviceUrl:
defaultZone: http://localhost:8081/eureka/
instance:
prefer-ip-address: true
- 创建监听器EurekaCacheRefreshListener.java，前面已经分析过HeartbeatEvent实例的两个成员变量，值为缓存刷新次数和CloudEurekaClient实例，在收到广播时，将这两个成员变量都在日志中打印出来：
@Component
public class EurekaCacheRefreshListener implements ApplicationListener<HeartbeatEvent> {
private static final Logger logger = LoggerFactory.getLogger(EurekaCacheRefreshListener.class);
@Override
public void onApplicationEvent(HeartbeatEvent event) {
Object count = event.getValue();
Object source = event.getSource();
logger.info("start onApplicationEvent, count [{}], source :\n{}", count, JSON.toJSON(source));
}
}
- 启动应用，等待大约30秒左右，EurekaCacheRefreshListener中的日志就会在控制台输出，内容十分丰富，建议您复制这些内容去在线格式化JSON的网站做一下格式化再来看，下面列出部分关键信息，其他的内容已经略去：
{
"instanceRemoteStatus": "UP",
"lastSuccessfulHeartbeatTimePeriod": 316,
"allKnownRegions": [
"us-east-1"
],
...
此处省略部分内容
...
"applications": {
"appsHashCode": "UP_1_",
"registeredApplications": [
{
"instances": [
{
"hostName": "192.168.31.104",
"overriddenStatus": "UNKNOWN",
"metadata": {
"jmx.port": "64656",
"management.port": "8085"
},
"statusPageUrl": "http://192.168.31.104:8085/info",
"secureVipAddress": "springcloud-customize-listener",
"leaseInfo": {
"renewalIntervalInSecs": 30,
"registrationTimestamp": 1537827838033,
"evictionTimestamp": 0,
"renewalTimestamp": 1537827987419,
"durationInSecs": 90,
"serviceUpTimestamp": 1537827837461
},
"homePageUrl": "http://192.168.31.104:8085/",
"countryId": 1,
"sID": "na",
"securePort": 443,
"dataCenterInfo": {
"name": "MyOwn"
},
"instanceId": "DESKTOP-82CCEBN:springcloud-customize-listener:8085",
"coordinatingDiscoveryServer": false,
"id": "DESKTOP-82CCEBN:springcloud-customize-listener:8085",
"vIPAddress": "springcloud-customize-listener",
"dirty": false,
"lastUpdatedTimestamp": 1537827838033,
"healthCheckUrl": "http://192.168.31.104:8085/health",
"appName": "SPRINGCLOUD-CUSTOMIZE-LISTENER",
"lastDirtyTimestamp": 1537827837401,
"iPAddr": "192.168.31.104",
"version": "unknown",
"actionType": "ADDED",
"port": 8085,
"healthCheckUrls": [
"http://192.168.31.104:8085/health"
],
"status": "UP"
}
]
启动springclouddeepprovider
- 应用springclouddeepprovider是最后一个启动的应用，启动该应用后，再去观察springcloudcustomizelistener的日志，发现应用springclouddeepprovider的注册信息已经获取到了：
{
"instances": [
{
"hostName": "192.168.119.1",
"overriddenStatus": "UNKNOWN",
"metadata": {
"jmx.port": "58420",
"management.port": "8082"
},
"statusPageUrl": "http://192.168.119.1:8082/info",
"secureVipAddress": "springcloud-deep-provider",
"leaseInfo": {
"renewalIntervalInSecs": 30,
"registrationTimestamp": 1537840715486,
"evictionTimestamp": 0,
"renewalTimestamp": 1537840715486,
"durationInSecs": 90,
"serviceUpTimestamp": 1537840715486
},
"homePageUrl": "http://192.168.119.1:8082/",
"countryId": 1,
"sID": "na",
"securePort": 443,
"dataCenterInfo": {
"name": "MyOwn"
},
"instanceId": "localhost:springcloud-deep-provider:8082",
"coordinatingDiscoveryServer": false,
"id": "localhost:springcloud-deep-provider:8082",
"vIPAddress": "springcloud-deep-provider",
"dirty": false,
"lastUpdatedTimestamp": 1537840715486,
"healthCheckUrl": "http://192.168.119.1:8082/health",
"appName": "SPRINGCLOUD-DEEP-PROVIDER",
"lastDirtyTimestamp": 1537840715451,
"iPAddr": "192.168.119.1",
"version": "unknown",
"actionType": "ADDED",
"port": 8082,
"healthCheckUrls": [
"http://192.168.119.1:8082/health"
],
"status": "UP"
}
],
"name": "SPRINGCLOUD-DEEP-PROVIDER",
"instancesAsIsFromEureka": [
{
"hostName": "192.168.119.1",
"overriddenStatus": "UNKNOWN",
"metadata": {
"jmx.port": "58420",
"management.port": "8082"
},
"statusPageUrl": "http://192.168.119.1:8082/info",
"secureVipAddress": "springcloud-deep-provider",
"leaseInfo": {
"renewalIntervalInSecs": 30,
"registrationTimestamp": 1537840715486,
"evictionTimestamp": 0,
"renewalTimestamp": 1537840715486,
"durationInSecs": 90,
"serviceUpTimestamp": 1537840715486
},
"homePageUrl": "http://192.168.119.1:8082/",
"countryId": 1,
"sID": "na",
"securePort": 443,
"dataCenterInfo": {
"name": "MyOwn"
},
"instanceId": "localhost:springcloud-deep-provider:8082",
"coordinatingDiscoveryServer": false,
"id": "localhost:springcloud-deep-provider:8082",
"vIPAddress": "springcloud-deep-provider",
"dirty": false,
"lastUpdatedTimestamp": 1537840715486,
"healthCheckUrl": "http://192.168.119.1:8082/health",
"appName": "SPRINGCLOUD-DEEP-PROVIDER",
"lastDirtyTimestamp": 1537840715451,
"iPAddr": "192.168.119.1",
"version": "unknown",
"actionType": "ADDED",
"port": 8082,
"healthCheckUrls": [
"http://192.168.119.1:8082/health"
],
"status": "UP"
}
]
}
- 至此，本次实战就完成了，通过开发自定义的广播监听器，我们对Eureka的注册发现机制有了进一步了解，在您的Spring Cloud学习过程中，希望本文能祝您一臂之力；
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