ZKUtil.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.zookeeper;

import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;

import org.apache.zookeeper.AsyncCallback.VoidCallback;
import org.apache.zookeeper.common.PathUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
         
public class ZKUtil {
    private static final Logger LOG = LoggerFactory.getLogger(ZKUtil.class);
    /**
     * Recursively delete the node with the given path. 
     * <p>
     * Important: All versions, of all nodes, under the given node are deleted.
     * <p>
     * If there is an error with deleting one of the sub-nodes in the tree, 
     * this operation would abort and would be the responsibility of the app to handle the same.
     * 
     * See {@link #delete(String, int)} for more details.
     * 
     * @throws IllegalArgumentException if an invalid path is specified
     */
    public static void deleteRecursive(ZooKeeper zk, final String pathRoot)
        throws InterruptedException, KeeperException
    {
        PathUtils.validatePath(pathRoot);
      
        List<String> tree = listSubTreeBFS(zk, pathRoot);
        LOG.debug("Deleting " + tree);
        LOG.debug("Deleting " + tree.size() + " subnodes ");
        for (int i = tree.size() - 1; i >= 0 ; --i) {
            //Delete the leaves first and eventually get rid of the root
            zk.delete(tree.get(i), -1); //Delete all versions of the node with -1.
        }
    }
    

    /**
     * Recursively delete the node with the given path. (async version).
     * 
     * <p>
     * Important: All versions, of all nodes, under the given node are deleted.
     * <p>
     * If there is an error with deleting one of the sub-nodes in the tree, 
     * this operation would abort and would be the responsibility of the app to handle the same.
     * <p>
     * @param zk the zookeeper handle
     * @param pathRoot the path to be deleted
     * @param cb call back method
     * @param ctx the context the callback method is called with
     * @throws IllegalArgumentException if an invalid path is specified
     */
    public static void deleteRecursive(ZooKeeper zk, final String pathRoot, VoidCallback cb,
        Object ctx)
        throws InterruptedException, KeeperException
    {
        PathUtils.validatePath(pathRoot);
      
        List<String> tree = listSubTreeBFS(zk, pathRoot);
        LOG.debug("Deleting " + tree);
        LOG.debug("Deleting " + tree.size() + " subnodes ");
        for (int i = tree.size() - 1; i >= 0 ; --i) {
            //Delete the leaves first and eventually get rid of the root
            zk.delete(tree.get(i), -1, cb, ctx); //Delete all versions of the node with -1.
        }
    }
    
    /**
     * BFS Traversal of the system under pathRoot, with the entries in the list, in the 
     * same order as that of the traversal.
     * <p>
     * <b>Important:</b> This is <i>not an atomic snapshot</i> of the tree ever, but the
     *  state as it exists across multiple RPCs from zkClient to the ensemble.
     * For practical purposes, it is suggested to bring the clients to the ensemble 
     * down (i.e. prevent writes to pathRoot) to 'simulate' a snapshot behavior.   
     * 
     * @param zk the zookeeper handle
     * @param pathRoot The znode path, for which the entire subtree needs to be listed.
     * @throws InterruptedException 
     * @throws KeeperException 
     */
    public static List<String> listSubTreeBFS(ZooKeeper zk, final String pathRoot) throws 
        KeeperException, InterruptedException {
        Deque<String> queue = new LinkedList<String>();
        List<String> tree = new ArrayList<String>();
        queue.add(pathRoot);
        tree.add(pathRoot);
        while (true) {
            String node = queue.pollFirst();
            if (node == null) {
                break;
            }
            List<String> children = zk.getChildren(node, false);
            for (final String child : children) {
                final String childPath = node + "/" + child;
                queue.add(childPath);
                tree.add(childPath);
            }
        }
        return tree;
    }
    
}