大數據教程(3.9):zookeeper分佈式應用系統服務器上下線動態感知程序開發_

    以前在zookeeper介紹時,有提到過zookeeper的應用場景有服務器上下線動態感知、分佈式共享鎖等等。本節博主將爲你們提供一個分佈式服務動態感知的事例,在後期博主的開源項目中的本身開發遠程分佈式框架rpc服務也將使用。因此,你們必定要掌握這塊知識點。java

    對於還不清楚動態感知原理的請先看以前的文章大數據教程(3.3):zookeeper簡介apache

(1)分佈式服務端註冊centos

package com.empire.zookeeper.test.em_zookeeper.zkdist;

import java.util.concurrent.CountDownLatch;

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.data.Stat;
import org.apache.zookeeper.ZooKeeper;

public class DistributedServer {
	private static final String connectString = "centos-aaron-07:2181,centos-aaron-08:2181,centos-aaron-16:2181";
	private static final int sessionTimeout = 2000;
	private static final String parentNode = "/servers";
	private CountDownLatch connectedSemaphore = new CountDownLatch(1); 
	private ZooKeeper zk = null;

	/**
	 * 建立到zk的客戶端鏈接
	 * 
	 * @throws Exception
	 */
	public void getConnect() throws Exception {

		zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
			@Override
			public void process(WatchedEvent event) {
				// 收到事件通知後的回調函數(應該是咱們本身的事件處理邏輯)
				System.out.println(event.getType() + "---" + event.getPath());
				try {
					zk.getChildren("/", true);
					connectedSemaphore.countDown(); 
				} catch (Exception e) {
				}
			}
		});
		connectedSemaphore.await();
	}

	/**
	 * 向zk集羣註冊服務器信息
	 * 
	 * @param hostname
	 * @throws Exception
	 */
	public void registerServer(String hostname) throws Exception {
		Stat stat = zk.exists(parentNode, false);
		System.out.println(stat==null?"not exist":"exist");
		if(stat==null) {
			String parentNodeCreate = zk.create(parentNode , null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
		}

		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);
	}

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

		// 獲取zk鏈接
		DistributedServer server = new DistributedServer();
		server.getConnect();

		// 利用zk鏈接註冊服務器信息
		server.registerServer(args[0]);

		// 啓動業務功能
		server.handleBussiness(args[0]);

	}

}

(2)分佈式客戶端感知服務狀態服務器

package com.empire.zookeeper.test.em_zookeeper.zkdist;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;

import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

public class DistributedClient {

	private static final String connectString = "centos-aaron-07:2181,centos-aaron-08:2181,centos-aaron-16:2181";
	private static final int sessionTimeout = 2000;
	private static final String parentNode = "/servers";
	// 注意:加volatile的意義何在?
	private volatile List<String> serverList;
	private CountDownLatch connectedSemaphore = new CountDownLatch(1); 
	private ZooKeeper zk = null;


	/**
	 * 建立到zk的客戶端鏈接
	 * 
	 * @throws Exception
	 */
	public void getConnect() throws Exception {

		zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
			@Override
			public void process(WatchedEvent event) {
				// 收到事件通知後的回調函數(應該是咱們本身的事件處理邏輯)
				try {
					//從新更新服務器列表,而且註冊了監聽
					getServerList();
					connectedSemaphore.countDown(); 
				} catch (Exception e) {
				}
			}
		});
		connectedSemaphore.await();
	}

	/**
	 * 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,而且對父節點進行監聽
		List<String> children = zk.getChildren(parentNode, true);

		// 先建立一個局部的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);
		
	}

	/**
	 * 業務功能
	 * 
	 * @throws InterruptedException
	 */
	public void handleBussiness() throws InterruptedException {
		System.out.println("client start working.....");
		Thread.sleep(Long.MAX_VALUE);
	}
	
	
	
	
	public static void main(String[] args) throws Exception {

		// 獲取zk鏈接
		DistributedClient client = new DistributedClient();
		client.getConnect();
		// 獲取servers的子節點信息(並監聽),從中獲取服務器信息列表
		client.getServerList();

		// 業務線程啓動
		client.handleBussiness();
		
	}

}

    注意點:在啓動server端上線時,須要輸入啓動參數hostname來啓動,該值用來惟一標識當前上線的是哪臺服務。session

    最後總結:其實分佈式服務動態感知主要運行zookeeper的短暫節點的的特性(服務器下線,zookeeper會自動刪除該服務器對於的臨時節點信息,並通知其它監聽了該節點變化的客戶端)來實現感知動態下線,以及zookeeper的節點監聽事件功能來實現感知服務動態上線。框架

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