https://blog.csdn.net/USTC_Zn/article/details/54974982

主體思路：

服務器端：服務器上線、在zookeeper創建 臨時的序列化結點

客戶端：已啟動getchildren 并注冊監聽 ,獲取到當前在線服務器列表。

效果：

客戶端能動態感知服務器上下線情況、并獲取新的服務器列表

?

服務器端源碼：

?

[java] view plaincopy

package?com.zn.zk1;??

??

import?org.apache.zookeeper.CreateMode;??

import?org.apache.zookeeper.WatchedEvent;??

import?org.apache.zookeeper.Watcher;??

import?org.apache.zookeeper.ZooDefs.Ids;??

import?org.apache.zookeeper.ZooKeeper;??

??

public?class?DistributedServer?{??

????private?static?final?String?connectString?=?"zk01:2181,zk02:2181,zk03:2181";??

????private?static?final?int?sessionTimeout?=?2000;??

????private?static?final?String?parentNode?=?"/servers";??

??

????private?ZooKeeper?zk?=?null;??

??????

??????

????/**?

?????*?模擬服務器上線?

?????*?@param?args?

?????*?@throws?Exception?

?????*/??

????public?static?void?main(String[]?args)?throws?Exception?{??

??

????????//?獲取zk連接??

????????DistributedServer?server?=?new?DistributedServer();??

????????server.getConnect();??

??

????????//?利用zk連接注冊服務器信息??

????????server.registerServer(args[0]);??

??

????????//?啟動業務功能??

????????server.handleBussiness(args[0]);??

??

????}??

????/**?

?????*?創建到zk的客戶端連接?

?????*??

?????*?@throws?Exception?

?????*/??

????public?void?getConnect()?throws?Exception?{??

??

????????zk?=?new?ZooKeeper(connectString,?sessionTimeout,?new?Watcher()?{??

??????????????

????????????public?void?process(WatchedEvent?event)?{??

????????????????//?收到事件通知后的回調函數（應該是我們自己的事件處理邏輯）??

????????????????System.out.println(event.getType()?+?"---"?+?event.getPath());??

????????????????try?{??

????????????????????zk.getChildren("/",?true);??

????????????????}?catch?(Exception?e)?{??

????????????????}??

????????????}??

????????});??

??

????}??

??

????/**?

?????*?向zk集群注冊服務器信息?

?????*??

?????*?@param?hostname?

?????*?@throws?Exception?

?????*/??

????public?void?registerServer(String?hostname)?throws?Exception?{??

??????????

????????//運行時請手動創建父節點/servers??

????????//臨時的臨時的序列化結點??

????????String?create?=?zk.create(parentNode?+?"/server",?hostname.getBytes(),?Ids.OPEN_ACL_UNSAFE,?CreateMode.EPHEMERAL_SEQUENTIAL);??

????????System.out.println(hostname?+?"is?online.."?+?create);??

??

????}??

??

????/**?

?????*?業務功能?

?????*??

?????*?@throws?InterruptedException?

?????*/??

????public?void?handleBussiness(String?hostname)?throws?InterruptedException?{??

????????System.out.println(hostname?+?"start?working.....");??

????????Thread.sleep(Long.MAX_VALUE);????

????}??

??

??

??

}??

-----------------------華麗的分界線---------------------

客戶端源碼：

?

[java] view plaincopy

package?com.zn.zk1;??

??

import?java.util.ArrayList;??

import?java.util.List;??

??

import?org.apache.zookeeper.KeeperException;??

import?org.apache.zookeeper.WatchedEvent;??

import?org.apache.zookeeper.Watcher;??

import?org.apache.zookeeper.ZooKeeper;??

??

public?class?DistributedClient?{??

??

????private?static?final?String?connectString?=?"zk01:2181,zk02:2181,zk03:2181";??

????private?static?final?int?sessionTimeout?=?2000;??

????private?static?final?String?parentNode?=?"/servers";??

??????

????/**?注意:加<span?style="color:#ff0000;"><strong>volatile的意義</strong></span>何在？---serverList對象在JVM堆中，多線程時會對該對象進行更改，每個線程對該對象操作會?

?????*??????copy一個副本到本地線程棧，再對該對象進行修改操作，改完后，再將該對象同步到共享的堆內存中。?

?????*?????被volatile修飾的對象則不會被copy到本地線程棧。所有線程看到的該對象是同一個。不會出現多線程問題。?

?????*/??

????private?volatile?List<String>?serverList;??

????private?ZooKeeper?zk?=?null;??

??????

??????

????public?static?void?main(String[]?args)?throws?Exception?{??

??

????????//?獲取zk連接??

????????DistributedClient?client?=?new?DistributedClient();??

??????????

????????//創建zookeeper連接??

????????client.getConnect();??

??????????

????????//?獲取servers的子節點信息（并監聽），從中獲取服務器信息列表??

????????client.getServerList();??

??

????????//?業務線程啟動??

????????client.handleBussiness();??

??????????

????}??

??

????/**?

?????*?業務功能?

?????*??

?????*?@throws?InterruptedException?

?????*/??

????public?void?handleBussiness()?throws?InterruptedException?{??

????????System.out.println("client?start?working.....");??

????????Thread.sleep(Long.MAX_VALUE);??

????}??

??

????/**?

?????*?創建到zk的客戶端連接?

?????*?@throws?Exception?

?????*/??

????public?void?getConnect()?throws?Exception?{??

??

????????zk?=?new?ZooKeeper(connectString,?sessionTimeout,?new?Watcher()?{??

??????????????

????????????public?void?process(WatchedEvent?event)?{??

????????????????//?收到事件通知后的回調函數（應該是我們自己的事件處理邏輯）??

????????????????try?{??

????????????????????//重新更新服務器列表，并且注冊了監聽??

????????????????????getServerList();??

??

????????????????}?catch?(Exception?e)?{??

????????????????}??

????????????}??

????????});??

??

????}??

??

????/**?

?????*?獲取服務器信息列表?

?????*??

?????*?@throws?Exception?

?????*/??

????public?void?getServerList()?throws?Exception?{??

??

????????//?獲取服務器子節點信息，并且對父節點進行監聽??

????????List<String>?children?=?zk.getChildren(parentNode,?true);??

??

????????//?先創建一個局部的list來存服務器信息??

????????List<String>?servers?=?new?ArrayList<String>();??

????????for?(String?child?:?children)?{??

????????????//?child只是子節點的節點名??

????????????byte[]?data?=?zk.getData(parentNode?+?"/"?+?child,?false,?null);??

????????????servers.add(new?String(data));??

????????}??

????????//?把servers賦值給成員變量serverList，已提供給各業務線程使用??

????????serverList?=?servers;??

??????????

????????//打印服務器列表??

????????System.out.println(serverList);??

??????????

????}??

}??

最后：可以將兩個java文件分別打包、部署到服務器測試、也可以在IDE上測試執行效果。

轉載于:https://www.cnblogs.com/davidwang456/articles/8729355.html

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