Zookeeper api增刪改查節點

Exists - 檢查Znode的存在

ZooKeeper類提供了 exists 方法來檢查znode的存在。如果指定的znode存在，則返回一個znode的元數據。exists方法的簽名如下：

exists(String path, boolean watcher)

• path- Znode路徑

• watcher - 布爾值，用於指定是否監視指定的znode

讓我們創建一個新的Java應用程序來檢查ZooKeeper API的“exists”功能。創建文件“ZKExists.java”。在main方法中，使用“ZooKeeperConnection”對象創建ZooKeeper對象“zk”。然后，使用自定義“path”調用“zk”對象的“exists”方法。完整的列表如下：

編碼：ZKExists.java

import java.io.IOException;

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 ZKExists {
   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 znode to the specified path
			
      try {
         conn = new ZooKeeperConnection();
         zk = conn.connect("localhost");
         Stat stat = znode_exists(path); // Stat checks the path of the znode
				
         if(stat != null) {
            System.out.println("Node exists and the node version is " +
            stat.getVersion());
         } else {
            System.out.println("Node does not exists");
         }
				
      } catch(Exception e) {
         System.out.println(e.getMessage()); // Catches error messages
      }
   }
}

一旦編譯和執行應用程序，你將獲得以下輸出。

Node exists and the node version is 1.

getData方法

ZooKeeper類提供 getData 方法來獲取附加在指定znode中的數據及其狀態。 getData 方法的簽名如下：

getData(String path, Watcher watcher, Stat stat)

• path - Znode路徑。

• watcher - 監視器類型的回調函數。當指定的znode的數據改變時，ZooKeeper集合將通過監視器回調進行通知。這是一次性通知。

• stat - 返回znode的元數據。

讓我們創建一個新的Java應用程序來了解ZooKeeper API的 getData 功能。創建文件 ZKGetData.java 。在main方法中，使用 ZooKeeperConnection 對象創建一個ZooKeeper對象 zk 。然后，使用自定義路徑調用zk對象的 getData 方法。

下面是從指定節點獲取數據的完整程序代碼：

編碼：ZKGetData.java

import java.io.IOException;
import java.util.concurrent.CountDownLatch;

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 ZKGetData {

   private static ZooKeeper zk;
   private static ZooKeeperConnection conn;
   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";
      final CountDownLatch connectedSignal = new CountDownLatch(1);
		
      try {
         conn = new ZooKeeperConnection();
         zk = conn.connect("localhost");
         Stat stat = znode_exists(path);
			
         if(stat != null) {
            byte[] b = zk.getData(path, new Watcher() {
				
               public void process(WatchedEvent we) {
					
                  if (we.getType() == Event.EventType.None) {
                     switch(we.getState()) {
                        case Expired:
                        connectedSignal.countDown();
                        break;
                     }
							
                  } else {
                     String path = "/MyFirstZnode";
							
                     try {
                        byte[] bn = zk.getData(path,
                        false, null);
                        String data = new String(bn,
                        "UTF-8");
                        System.out.println(data);
                        connectedSignal.countDown();
							
                     } catch(Exception ex) {
                        System.out.println(ex.getMessage());
                     }
                  }
               }
            }, null);
				
            String data = new String(b, "UTF-8");
            System.out.println(data);
            connectedSignal.await();
				
         } else {
            System.out.println("Node does not exists");
         }
      } catch(Exception e) {
        System.out.println(e.getMessage());
      }
   }
}

一旦編譯和執行應用程序，你將獲得以下輸出

My first zookeeper app

應用程序將等待ZooKeeper集合的進一步通知。使用ZooKeeper CLI zkCli.sh 更改指定znode的數據。

cd /path/to/zookeeper
bin/zkCli.sh
>>> set /MyFirstZnode Hello

現在，應用程序將打印以下輸出並退出。

Hello

setData方法

ZooKeeper類提供 setData 方法來修改指定znode中附加的數據。 setData 方法的簽名如下：

setData(String path, byte[] data, int version)

• path- Znode路徑

• data - 要存儲在指定znode路徑中的數據。

• version- znode的當前版本。每當數據更改時，ZooKeeper會更新znode的版本號。

現在讓我們創建一個新的Java應用程序來了解ZooKeeper API的 setData 功能。創建文件 ZKSetData.java。在main方法中，使用 ZooKeeperConnection 對象創建一個ZooKeeper對象 zk 。然后，使用指定的路徑，新數據和節點版本調用 zk 對象的 setData 方法。

以下是修改附加在指定znode中的數據的完整程序代碼。

編碼：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());
      }
   }
}

編譯並執行應用程序后，指定的znode的數據將被改變，並且可以使用ZooKeeper CLI zkCli.sh 進行檢查。

cd /path/to/zookeeper
bin/zkCli.sh
>>> get /MyFirstZnode

getChildren方法

ZooKeeper類提供 getChildren 方法來獲取特定znode的所有子節點。 getChildren 方法的簽名如下：

getChildren(String path, Watcher watcher)

• path - Znode路徑。

• watcher - 監視器類型的回調函數。當指定的znode被刪除或znode下的子節點被創建/刪除時，ZooKeeper集合將進行通知。這是一次性通知。

編碼：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());
      }

   }

}

在運行程序之前，讓我們使用ZooKeeper CLI zkCli.sh 為 /MyFirstZnode 創建兩個子節點。

cd /path/to/zookeeper
bin/zkCli.sh
>>> create /MyFirstZnode/myfirstsubnode Hi
>>> create /MyFirstZnode/mysecondsubmode Hi

現在，編譯和運行程序將輸出上面創建的znode。

myfirstsubnode
mysecondsubnode

刪除Znode

ZooKeeper類提供了 delete 方法來刪除指定的znode。 delete 方法的簽名如下：

delete(String path, int version)

• path - Znode路徑。

• version - znode的當前版本。

讓我們創建一個新的Java應用程序來了解ZooKeeper API的 delete 功能。創建文件 ZKDelete.java 。在main方法中，使用 ZooKeeperConnection 對象創建一個ZooKeeper對象 zk 。然后，使用指定的路徑和版本號調用 zk 對象的 delete 方法。

刪除znode的完整程序代碼如下：

編碼：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
      }
   }
}