实战监听Eureka client的缓存更新

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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：

1. 《spring4.1.8扩展实战之三：广播与监听 》
2. 《Spring Cloud源码分析之Eureka篇第五章：更新服务列表 》

实战内容

• 本文是一篇实战的文章，实战内容如下：

1. 启动Eureka server；
2. 开发一个应用springcloudcustomizelistener，启动后会注册到Eureka server；
3. 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）；
4. 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）；
5. 存入缓存后，会在spring容器内发送广播（已有逻辑）；
6. 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；
7. 再启动另一个应用springclouddeepprovider，也会注册到Eureka server；
8. 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：

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"
                    }
                ]

• 如上所示，当前应用的实例信息在本地已经缓存了；

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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