大数据学习笔记-------------------(12_2)

11.7 setData方法

zookeeper类提供setData方法来修改附着在指定znode的数据。setData方法：

setData(String path, byte[] data, int version)<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">  </span>

参数解释说明：

path-----------znode路径

data-----------存储在指定znode路径的数据

version-------znode当前版本。只要数据发生改变，zookeeper就会更新znode的版本号

创建一个新的Java应用程序帮助理解ZooKeeperAPI的setData函数。创建一个文件ZKSetData.java。在main方法中，使用ZooKeeperConnection对象创建一个ZooKeeper对象ZK。然后，调用ZK对象的SetData方法：指定路径、新数据、该节点的版本。

下面是完整的程序代码来修改附加在指定znode数据：ZKSetData.java 

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import java.io.IOException;
public class ZKSetData {
private static ZooKeeper zk;
private static ZooKeeperConnection conn;
// Method to update the data in a znode. Similar to getData but without watcher.
public static void update(String path, byte[] data) throws KeeperException,InterruptedException {
zk.setData(path, data, zk.exists(path,true).getVersion());
}
public static void main(String[] args) throws InterruptedException,KeeperException {
String path= "/MyFirstZnode";
byte[] data = "Success".getBytes(); //Assign data which is to be updated.
try {
conn = new ZooKeeperConnection();
zk = conn.connect("localhost");
update(path, data); // Update znode data to the specified path
      }
catch(Exception e) {
System.out.println(e.getMessage());
}
}
}

一旦编译并运行，使用zookeeperCLI zkCli.sh检查指定znode数据变化：

 启动客服端：bin/zkCli.sh start

 调用get：get /MyFirstZnode

11.8 getChildren 方法

zookeeper类提供的getChildren方法来获取指定znode的所有子节点。getChildren方法：

getChildren(String path, Watcher watcher)<span style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; background-color: rgb(255, 255, 255);">       </span><span style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; background-color: rgb(255, 255, 255);">    </span>

参数解释说明：

path----------znode路径​

watcher----调用类型为watcher函数。当指定znode被删除或znode以下的children被创建/删除时，zookeeper ensemble会通知。只会通知一次​

代码：ZKGetChildren.java

import java.io.IOException;
import java.util.*;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.data.Stat;
public class ZKGetChildren {
private static ZooKeeper zk;
private static ZooKeeperConnection conn;
// Method to check existence of znode and its status, if znode is available.
public static Stat znode_exists(String path) throws KeeperException,InterruptedException {
return zk.exists(path,true);
}
public static void main(String[] args) throws InterruptedException,KeeperException {
String path= "/MyFirstZnode"; // Assign path to the znode
try {
conn = new ZooKeeperConnection();
zk = conn.connect("localhost");
Stat stat = znode_exists(path); // Stat checks the path
if(stat!= null) {
//“getChildren” method- get all the children of znode.It has two args, path and watch
List<String> children = zk.getChildren(path, false);
for(int i = 0; i < children.size(); i++)
System.out.println(children.get(i)); //Print children's
} else {
System.out.println("Node does not exists");
}
}
catch(Exception e) {
System.out.println(e.getMessage());
}
}
}

在运行程序之前，使用ZooKeeper CLI，zkCli.sh为/MyFirstZnode创建两个子节点：

启动客服端：bin/zkCli.sh start

调用create：

create/MyFirstZnode/myfirstsubnode Hi   
create /MyFirstZnode/mysecondsubmode Hi

现在，编译和运行程序的输出上面创建的znodes：myfirstsubnode 、mysecondsubnode

11.9 删除Znode

 zookeeper类提供delete方法来删除指定znode。Delete方法：

delete(String path, int version)

参数解释说明：

path------znode路径

version---当前znode的版本

 创建一个新的Java应用程序帮助理解ZooKeeperAPI的delete函数。创建一个文件ZKDelete.java。在main方法中，使用ZooKeeperConnection对象创建一个ZooKeeper对象ZK。然后，调用ZK对象的delete方法:节点的指定路径和版本。

完整的程序代码来删除一个znode如下：ZKDelete.java

import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.KeeperException;
public class ZKDelete {
   private static ZooKeeper zk;
private static ZooKeeperConnection conn;
// Method to check existence of znode and its status, if znode is available.
public static void delete(String path) throws KeeperException,InterruptedException {
zk.delete(path,zk.exists(path,true).getVersion());
}
public static void main(String[] args) throws InterruptedException,KeeperException {
String path= "/MyFirstZnode"; //Assign path to the znode
try{
conn = new ZooKeeperConnection();
zk = conn.connect("localhost");
delete(path); //delete the node with the specified path
}
catch(Exception e) {
System.out.println(e.getMessage()); // catches error messages
}
}
}