Java tutorial
/* * Copyright 2012 Netflix, Inc. * * Licensed 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 zookeeper.example.cache; import com.google.common.collect.Lists; import com.google.common.io.Closeables; import com.netflix.curator.framework.CuratorFramework; import com.netflix.curator.framework.CuratorFrameworkFactory; import com.netflix.curator.framework.recipes.cache.ChildData; import com.netflix.curator.framework.recipes.cache.PathChildrenCache; import com.netflix.curator.framework.recipes.cache.PathChildrenCacheEvent; import com.netflix.curator.framework.recipes.cache.PathChildrenCacheListener; import com.netflix.curator.retry.ExponentialBackoffRetry; import com.netflix.curator.test.TestingServer; import com.netflix.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 { Closeables.closeQuietly(cache); Closeables.closeQuietly(client); Closeables.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 command = in.readLine().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) { Closeables.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().creatingParentsIfNeeded().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("delete: List the nodes/values in the cache"); System.out.println("quit: Quit the example"); System.out.println(); } }