本文来介绍原生的API来操作ZK节点，从而引出下节要说明的Curator客户端。
环境准备
新建一个普通的java项目即可，然后引入一些jar包的依赖：
代码在code-for-chapter9
客户端与ZK建立连接
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| import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import java.io.IOException;
public class ZKConnect implements Watcher {
public static void main(String[] args) throws IOException {
String serverPath = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
ZooKeeper zk = new ZooKeeper(serverPath,5*1000,new ZKConnect());
System.out.println("客户端开始连接zk...，连接状态为:"+zk.getState());
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("连接状态为:"+zk.getState());
}
@Override
public void process(WatchedEvent watchedEvent) {
System.out.println("接受到的watch通知："+watchedEvent);
}
}
|
会话重连机制
主要的思路就是上一个程序注释中所描述:用上一次连接的sessionId和sessionPasswd这两个参数代入到下次连接中，就可以重新获取上一次的连接了。
下面就是不断地看seesionId来判断是否为同一个连接。
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| public class ZKConnectSessionWatcher implements Watcher {
public static void main(String[] args) throws IOException {
String serverPath = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
long sessionId = 999L;
byte[] sessionPasswd = null;
ZooKeeper zk = new ZooKeeper(serverPath,5*1000,new ZKConnectSessionWatcher());
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (zk.getState().equals(ZooKeeper.States.CONNECTED)){
sessionId = zk.getSessionId();
System.out.println(sessionId);
String ssid = "0x" + Long.toHexString(sessionId);
System.out.println(ssid);
sessionPasswd = zk.getSessionPasswd();
}
System.out.println("会话重连...");
ZooKeeper zkSession = new ZooKeeper(serverPath,5*1000,new ZKConnectSessionWatcher(),sessionId,sessionPasswd);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("重连之后的sessionId为："+zkSession.getSessionId());
}
@Override
public void process(WatchedEvent watchedEvent) {
System.out.println("接受到的watch通知："+watchedEvent);
}
}
|
节点的增删改查
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| public class ZKNodeOperator implements Watcher {
final static String serverPath = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
private ZooKeeper zooKeeper = null;
public ZooKeeper getZooKeeper(){
return zooKeeper;
}
public void setZooKeeper(ZooKeeper zooKeeper){
this.zooKeeper = zooKeeper;
}
public ZKNodeOperator(){}
public ZKNodeOperator(String connectionString,int sessionTimeout){
try {
zooKeeper = new ZooKeeper(connectionString,sessionTimeout,new ZKNodeOperator());
} catch (IOException e) {
e.printStackTrace();
if(zooKeeper != null){
try {
zooKeeper.close();
} catch (InterruptedException e1) {
e1.printStackTrace();
}
}
}
}
public static void main(String[] args) {
ZKNodeOperator zkServer = new ZKNodeOperator(serverPath,5*1000);
String ctx = "{'delete':'success'}";
zkServer.getZooKeeper().delete("/testNode1",0,new DeleteCallBack(),ctx);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@Override
public void process(WatchedEvent watchedEvent) {
System.out.println("watch被触发..."+watchedEvent);
}
}
|
countDownLatch
上面学习了对于节点的增删改，还差一个查，这里先学习一下countDownLatch：
demo的场景是：有一个监控中心，监控很多地方的调度中心的情况，每检查一个，就返回一个状态，直到所有的调度中心都检查完。
代码在文件夹countdownlatchdemo.
这个玩意就是一个计数器。引入这个玩意，是为了配合下面的案例，使得线程能挂起，我们可以测试数据变化一下，然后触发watcher,拿到变化后的值，然后主线程执行结束。
获取父节点数据
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| public class ZKGetNodeData implements Watcher {
private ZooKeeper zooKeeper;
final static String serverPath = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
private static Stat stat = new Stat();
private static CountDownLatch countDownLatch = new CountDownLatch(1);
public ZKGetNodeData(){}
public ZKGetNodeData(String connectionString,int sessionTimeout){
try {
zooKeeper = new ZooKeeper(connectionString,sessionTimeout,new ZKGetNodeData());
} catch (IOException e) {
e.printStackTrace();
if(zooKeeper != null){
try {
zooKeeper.close();
} catch (InterruptedException e1) {
e1.printStackTrace();
}
}
}
}
public static void main(String[] args) throws InterruptedException, KeeperException {
ZKGetNodeData zkServer = new ZKGetNodeData(serverPath,5*1000);
byte[] resByte = zkServer.getZooKeeper().getData("/hello",true,stat);
String result = new String(resByte);
System.out.println("当前值:"+result);
countDownLatch.await();
}
@Override
public void process(WatchedEvent event) {
try {
if(event.getType() == Event.EventType.NodeDataChanged){
ZKGetNodeData zkServer = new ZKGetNodeData(serverPath,5*1000);
byte[] resByte = zkServer.getZooKeeper().getData("/hello",true,stat);
String result = new String(resByte);
System.out.println("更改后的值："+result);
System.out.println("版本："+stat.getVersion());
countDownLatch.countDown();
}else if(event.getType() == Event.EventType.NodeCreated){
}else if(event.getType() == Event.EventType.NodeChildrenChanged){
}else if(event.getType() == Event.EventType.NodeDeleted){
}
}catch (Exception e){
e.printStackTrace();
}
}
public ZooKeeper getZooKeeper() {
return zooKeeper;
}
public void setZooKeeper(ZooKeeper zooKeeper) {
this.zooKeeper = zooKeeper;
}
}
|
获取子节点数据
基本同上，见代码ZKGetChildrenList
判断节点是否存在
基本同上，见代码ZKNodeExist。
