Zookeeper:API(二)
检查Znode的存在
ZooKeeper类提供了exists方法来检查znode的存在。如果指定的znode存在,它将返回znode的元数据。exists方法如下
exists(String path, boolean watcher)
其中,
path: Znode路径
watcher :布尔值,用于指定是否查看指定的znode
让我们创建一个新的Java应用程序来检查ZooKeeper API的exists功能。创建一个文件“ZKExists.java”。在main方法中,使用“ZooKeeperConnection”对象创建zk对象。然后,用自定义的path调用“zk”对象的exists方法。完整列表如下
//Coding: 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 } } }
一旦应用程序被编译和执行,您将得到下面的输出。
Node exists and the node version is 1.
getData方法
ZooKeeper类提供getData方法来获取指定znode中附加的数据及其状态。getData方法如下
getData(String path, Watcher watcher, Stat stat)
其中;
path:Znode路径
watcher:类型监视器的回调函数。当指定znode的数据发生变化时,ZooKeeper集成将通过监视器回调进行通知。这是一次性通知
stat:返回znode的元数据。
让我们创建一个新的Java应用程序来理解ZooKeeper应用程序接口的getData功能。创建一个文件ZKGetData.java。在主方法中,使用ZooKeeperConnection对象创建一个ZooKeeper对象zk。然后,用自定义路径调用zk对象的getData方法。
以下是从指定节点获取数据的完整程序代码:
//Coding: 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()); } } }
一旦编译并执行了应用程序,您将获得以下输出:
My first zookeeper app
应用程序将等待ZooKeeper的进一步通知。使用ZooKeeper CLI更改指定znode的数据
cd /path/to/zookeeper bin/zkCli.sh >>> set /MyFirstZnode Hello
现在,应用程序将打印以下输出并退出。
Hello
setData方法
ZooKeeper类提供setData方法来修改指定znode中附加的数据。setData方法如下:
setData(String path, byte[] data, int version)
其中,
path:Znode路径
data:要存储在指定znode路径中的数据。
version:znode的当前版本。每当数据发生变化时,ZooKeeper都会更新znode的版本号。
现在让我们创建一个新的Java应用程序来理解ZooKeeper应用程序接口的设置数据功能。创建一个文件ZKSetData.java。在主方法中,使用ZooKeeperConnection对象创建zk。然后,用指定的路径、新数据和节点版本调用zk对象的setData方法。
以下是修改指定znode中附加数据的完整程序代码。
//Code: 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()); } } }
一旦应用程序被编译和执行,指定znode的数据将被更改,并且可以使用ZooKeeper CLI检查它
cd /path/to/zookeeper bin/zkCli.sh >>> get /MyFirstZnode
getChildren方法
ZooKeeper类提供getChildren方法来获取特定znode的所有子节点。getChildren方法如下:
getChildren(String path, Watcher watcher)
其中
path:Znode路径
watcher:Watcher类型的回调函数。ZooKeeper集成将在指定的znode被删除或znode下的子节点被创建/删除时发出通知。这是一次性通知。
//Coding: 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,让我们使用ZkKeep CLI为/MyFirstZnode创建两个子节点
cd /path/to/zookeeper bin/zkCli.sh >>> create /MyFirstZnode/myfirstsubnode Hi >>> create /MyFirstZnode/mysecondsubmode Hi
现在,编译和运行程序将输出上面创建的znodes。
myfirstsubnode mysecondsubnode
删除Znode
ZooKeeper类提供delete方法来删除指定的znode。删除方法的签名如下
delete(String path, int version)
其中,
path:Znode路径.
version:znode的当前版本.
让我们创建一个新的Java应用程序来理解ZooKeeper应用程序接口的删除功能。创建一个文件ZKDelete.java。在主方法中,使用ZooKeeperConnection对象创建zk。然后,用指定的路径和节点版本调用zk对象的delete方法。
删除znode的完整程序代码如下:
//Coding: 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 } } }