curator-examples/src/main/java/cache/PathCacheExample.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 cache;

import com.google.common.collect.Lists;
import org.apache.curator.utils.CloseableUtils;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.ChildData;
import org.apache.curator.framework.recipes.cache.PathChildrenCache;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.test.TestingServer;
import org.apache.curator.utils.ZKPaths;
import discovery.ExampleServer;
import org.apache.zookeeper.KeeperException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.List;

/**
 * An example of the PathChildrenCache. The example "harness" is a command processor
 * that allows adding/updating/removed nodes in a path. A PathChildrenCache keeps a
 * cache of these changes and outputs when updates occurs.
 */
public class PathCacheExample
{
    private static final String     PATH = "/example/cache";

    public static void main(String[] args) throws Exception
    {
        TestingServer       server = new TestingServer();
        CuratorFramework    client = null;
        PathChildrenCache   cache = null;
        try
        {
            client = CuratorFrameworkFactory.newClient(server.getConnectString(), new ExponentialBackoffRetry(1000, 3));
            client.start();

            // in this example we will cache data. Notice that this is optional.
            cache = new PathChildrenCache(client, PATH, true);
            cache.start();

            processCommands(client, cache);
        }
        finally
        {
            CloseableUtils.closeQuietly(cache);
            CloseableUtils.closeQuietly(client);
            CloseableUtils.closeQuietly(server);
        }
    }

    private static void addListener(PathChildrenCache cache)
    {
        // a PathChildrenCacheListener is optional. Here, it's used just to log changes
        PathChildrenCacheListener listener = new PathChildrenCacheListener()
        {
            @Override
            public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception
            {
                switch ( event.getType() )
                {
                    case CHILD_ADDED:
                    {
                        System.out.println("Node added: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                        break;
                    }

                    case CHILD_UPDATED:
                    {
                        System.out.println("Node changed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                        break;
                    }

                    case CHILD_REMOVED:
                    {
                        System.out.println("Node removed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                        break;
                    }
                }
            }
        };
        cache.getListenable().addListener(listener);
    }

    private static void processCommands(CuratorFramework client, PathChildrenCache cache) throws Exception
    {
        // More scaffolding that does a simple command line processor

        printHelp();

        List<ExampleServer> servers = Lists.newArrayList();
        try
        {
            addListener(cache);

            BufferedReader  in = new BufferedReader(new InputStreamReader(System.in));
            boolean         done = false;
            while ( !done )
            {
                System.out.print("> ");

                String      line = in.readLine();
                if ( line == null )
                {
                    break;
                }

                String      command = line.trim();
                String[]    parts = command.split("\\s");
                if ( parts.length == 0 )
                {
                    continue;
                }
                String      operation = parts[0];
                String      args[] = Arrays.copyOfRange(parts, 1, parts.length);

                if ( operation.equalsIgnoreCase("help") || operation.equalsIgnoreCase("?") )
                {
                    printHelp();
                }
                else if ( operation.equalsIgnoreCase("q") || operation.equalsIgnoreCase("quit") )
                {
                    done = true;
                }
                else if ( operation.equals("set") )
                {
                    setValue(client, command, args);
                }
                else if ( operation.equals("remove") )
                {
                    remove(client, command, args);
                }
                else if ( operation.equals("list") )
                {
                    list(cache);
                }

                Thread.sleep(1000); // just to allow the console output to catch up
            }
        }
        finally
        {
            for ( ExampleServer server : servers )
            {
                CloseableUtils.closeQuietly(server);
            }
        }
    }

    private static void list(PathChildrenCache cache)
    {
        if ( cache.getCurrentData().size() == 0 )
        {
            System.out.println("* empty *");
        }
        else
        {
            for ( ChildData data : cache.getCurrentData() )
            {
                System.out.println(data.getPath() + " = " + new String(data.getData()));
            }
        }
    }

    private static void remove(CuratorFramework client, String command, String[] args) throws Exception
    {
        if ( args.length != 1 )
        {
            System.err.println("syntax error (expected remove <path>): " + command);
            return;
        }

        String      name = args[0];
        if ( name.contains("/") )
        {
            System.err.println("Invalid node name" + name);
            return;
        }
        String      path = ZKPaths.makePath(PATH, name);

        try
        {
            client.delete().forPath(path);
        }
        catch ( KeeperException.NoNodeException e )
        {
            // ignore
        }
    }

    private static void setValue(CuratorFramework client, String command, String[] args) throws Exception
    {
        if ( args.length != 2 )
        {
            System.err.println("syntax error (expected set <path> <value>): " + command);
            return;
        }

        String      name = args[0];
        if ( name.contains("/") )
        {
            System.err.println("Invalid node name" + name);
            return;
        }
        String      path = ZKPaths.makePath(PATH, name);

        byte[]      bytes = args[1].getBytes();
        try
        {
            client.setData().forPath(path, bytes);
        }
        catch ( KeeperException.NoNodeException e )
        {
            client.create().creatingParentContainersIfNeeded().forPath(path, bytes);
        }
    }

    private static void printHelp()
    {
        System.out.println("An example of using PathChildrenCache. This example is driven by entering commands at the prompt:\n");
        System.out.println("set <name> <value>: Adds or updates a node with the given name");
        System.out.println("remove <name>: Deletes the node with the given name");
        System.out.println("list: List the nodes/values in the cache");
        System.out.println("quit: Quit the example");
        System.out.println();
    }
}