Java tutorial
/* * Copyright 1999-2004 The Apache Software Foundation * * 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 org.apache.slide.cluster; import java.util.Enumeration; import java.util.EventListener; import java.util.Iterator; import java.util.Map; import org.apache.commons.httpclient.Credentials; import org.apache.commons.httpclient.UsernamePasswordCredentials; import org.apache.commons.httpclient.protocol.Protocol; import org.apache.slide.authenticate.CredentialsToken; import org.apache.slide.authenticate.SecurityToken; import org.apache.slide.common.Domain; import org.apache.slide.common.NamespaceAccessToken; import org.apache.slide.common.SlideTokenImpl; import org.apache.slide.common.Uri; import org.apache.slide.store.ExtendedStore; import org.apache.slide.store.Store; import org.apache.slide.util.conf.Configurable; import org.apache.slide.util.conf.Configuration; import org.apache.slide.util.conf.ConfigurationException; import org.apache.slide.util.logger.Logger; import org.apache.webdav.lib.NotificationListener; import org.apache.webdav.lib.Subscriber; import org.apache.webdav.lib.methods.DepthSupport; /** * <h3>Description</h3> * <p> * When configured properly this class will register with one or more external * Slide instances and listen for changes. Upon notification of a change this * class will cause the cache of the local Slide instance to be refreshed for * the changed object. * </p> * <h3>Usage</h3> * <p> * Add the following to your Domain.xml inside the <events> node. * </p> * * <pre> * * * <listener classname="org.apache.slide.cluster.ClusterCacheRefresher"> * <configuration> * <node local-host="local.host.domain" * local-port="4444" * repository-host="remote.host.domain" * repository-port="8080" * repository-protocol="http" * username="root" * password="root" * /> * </configuration> * </listener> * * * </pre> * * <p> * There should be one <node> element for each node in the cluster, * <b>except </b> for the current node. ClusterCacheRefresher should not be * configured to listen to itself except for testing purposes. * </p> * <h3><node> attributes</h3> * <table> * <tr> * <th>Attribute Name</th> * <th>Required?</th> * <th>Default Value</th> * <th>Description</th> * </tr> * <tr> * <td>local-host</td> * <td>yes</td> * <td>none</td> * <td>A network-accessible name or ip-address where the remote Slide instance * can reach <b>this server. </b></td> * </tr> * <tr> * <td>local-port</td> * <td>yes</td> * <td>none</td> * <td>A port number ClusterCacheRefresher can use to listen for notifications. * <b>Must be unique. </b></td> * </tr> * <tr> * <td>repository-host</td> * <td>yes</td> * <td>none</td> * <td>A network-accessible name or ip-address of the remote Slide instance to * monitor.</td> * </tr> * <tr> * <td>repository-port</td> * <td>yes</td> * <td>none</td> * <td>The port the remote Slide instance is running on.</td> * </tr> * <tr> * <td>repository-protocol</td> * <td>no</td> * <td>http</td> * <td>The protocol the remote Slide instance is using. Must be one of "http" * or "https".</td> * </tr> * <tr> * <td>username</td> * <td>no</td> * <td>none</td> * <td>The username to use to connect to the remote Slide instance.</td> * </tr> * <tr> * <td>password</td> * <td>no</td> * <td>none</td> * <td>The password that goes with the username.</td> * </tr> * <tr> * <td>repository-domain</td> * <td>no</td> * <td>/slide</td> * <td>The context path of the remote Slide instance.</td> * </tr> * <tr> * <td>poll-interval</td> * <td>no</td> * <td>60000</td> * <td>The number of milliseconds to wait between polling the remote Slide * instance for any changes. Polling for changes is a backup only, so this value * can be set fairly high.</td> * </tr> * <tr> * <td>udp</td> * <td>no</td> * <td>true</td> * <td>Must be "true" or "false". Indicates whether to use udp or tcp to listen * for notifications.</td> * </tr> * <tr> * <td>base-uri</td> * <td>no</td> * <td>/</td> * <td>The base path to monitor for changes. Will be appended to the * repository-domain.</td> * </tr> * <tr> * <td>subscription-lifetime</td> * <td>no</td> * <td>3600</td> * <td>The number of seconds a subscription should last. Subscriptions are * automatically refreshed. Do not set this value too high.</td> * </tr> * <tr> * <td>notification-delay</td> * <td>no</td> * <td>0</td> * <td>Number of seconds the remote Slide instance should wait before sending a * notification of a change.</td> * </tr> * </table> */ public class ClusterCacheRefresher implements EventListener, Configurable { protected static final String LOG_CHANNEL = ClusterCacheRefresher.class.getName(); protected NotificationListener listener; public ClusterCacheRefresher() { Domain.log("Creating ClusterCacheRefresher", LOG_CHANNEL, Logger.INFO); } public void configure(Configuration configuration) throws ConfigurationException { Domain.log("Configuring ClusterCacheRefresher", LOG_CHANNEL, Logger.INFO); Enumeration nodes = configuration.getConfigurations("node"); while (nodes.hasMoreElements()) { Configuration node = (Configuration) nodes.nextElement(); final String host = node.getAttribute("local-host"); final int port = node.getAttributeAsInt("local-port"); final String repositoryHost = node.getAttribute("repository-host"); final int repositoryPort = node.getAttributeAsInt("repository-port"); String repositoryProtocolString = node.getAttribute("repository-protocol", "http"); final Protocol protocol; try { protocol = Protocol.getProtocol(repositoryProtocolString); } catch (IllegalStateException exception) { throw new ConfigurationException("Unknown repository-protocol: " + repositoryProtocolString + ". Must be \"http\" or \"https\".", configuration); } String username = node.getAttribute("username", ""); String password = node.getAttribute("password", ""); final Credentials credentials = new UsernamePasswordCredentials(username, password); final String repositoryDomain = node.getAttribute("repository-domain", "/slide"); final int pollInterval = node.getAttributeAsInt("poll-interval", 60000); final boolean udp = node.getAttributeAsBoolean("udp", true); final String uri = node.getAttribute("base-uri", "/"); final int depth = DepthSupport.DEPTH_INFINITY; final int lifetime = node.getAttributeAsInt("subscription-lifetime", 3600); final int notificationDelay = node.getAttributeAsInt("notification-delay", 0); final Subscriber contentSubscriber = new Subscriber() { public void notify(String uri, Map information) { NamespaceAccessToken nat = Domain.accessNamespace(new SecurityToken(this), Domain.getDefaultNamespace()); try { nat.begin(); Iterator keys = information.keySet().iterator(); while (keys.hasNext()) { String key = keys.next().toString(); if ("uri".equals(key)) { Uri theUri = nat.getUri(new SlideTokenImpl(new CredentialsToken("")), stripUri(information.get(key).toString())); Store store = theUri.getStore(); if (store instanceof ExtendedStore) { Domain.log("Resetting cache for " + theUri, LOG_CHANNEL, Logger.INFO); ((ExtendedStore) store).removeObjectFromCache(theUri); } } } nat.commit(); } catch (Exception e) { if (Domain.isEnabled(LOG_CHANNEL, Logger.ERROR)) { Domain.log("Error clearing cache: " + e + ". See stderr for stacktrace.", LOG_CHANNEL, Logger.ERROR); e.printStackTrace(); } } } }; final Subscriber structureSubscriber = new Subscriber() { public void notify(String uri, Map information) { NamespaceAccessToken nat = Domain.accessNamespace(new SecurityToken(this), Domain.getDefaultNamespace()); try { nat.begin(); Iterator keys = information.keySet().iterator(); while (keys.hasNext()) { String key = keys.next().toString(); if ("uri".equals(key)) { Uri theUri = nat.getUri(new SlideTokenImpl(new CredentialsToken("")), stripUri(information.get(key).toString())); Store store = theUri.getParentUri().getStore(); if (store instanceof ExtendedStore) { Domain.log("Resetting cache for " + theUri.getParentUri(), LOG_CHANNEL, Logger.INFO); ((ExtendedStore) store).removeObjectFromCache(theUri.getParentUri()); } } } nat.commit(); } catch (Exception e) { if (Domain.isEnabled(LOG_CHANNEL, Logger.ERROR)) { Domain.log("Error clearing cache: " + e + ". See stderr for stacktrace.", LOG_CHANNEL, Logger.ERROR); e.printStackTrace(); } } } }; /* * This needs to be done in a thread for three reasons: * 1) If NotificationListener.subscribe() connects to a Slide instance * that is in the process of starting it will wait until the server * has finished starting before it returns. If configuration is * single-thread this prevents this Slide instance from starting * until all other Slide instances have started. This means none * of them can start if they're all waiting for each other. Simple * test case of this is a cluster of one instance. It never starts. * 2) Allows for renewing of subscriptions. * 3) Allows for retrying failed subscriptions. This will happen if * a server is down and NotificationListener.subscribe() can't * reach it. */ Thread t = new Thread(new Runnable() { private boolean success; public void run() { success = true; listener = new NotificationListener(host, port, repositoryHost, repositoryPort, protocol, credentials, repositoryDomain, pollInterval, udp); success = listener.subscribe("Update", uri, depth, lifetime, notificationDelay, contentSubscriber, credentials); success = listener.subscribe("Update/newmember", uri, depth, lifetime, notificationDelay, structureSubscriber, credentials); success = listener.subscribe("Delete", uri, depth, lifetime, notificationDelay, structureSubscriber, credentials); success = listener.subscribe("Move", uri, depth, lifetime, notificationDelay, structureSubscriber, credentials); if (!success) { // try again quickly try { Thread.sleep(10000); } catch (InterruptedException e) { // ignore } } else { // try again before the subscriptions expire try { Thread.sleep(lifetime * 1000 - 60); } catch (InterruptedException e) { // ignore } } } }); t.setDaemon(true); t.start(); } } /** * Removes the first segment of a uri. "/slide/files/foo" becomes * "/files/foo". * * @param uri the uri to strip * @return the stipped uri */ private String stripUri(String uri) { // FIXME: if this is intended to remove the servlet path this will // NOT work if the servlet is not default-servlet or is the root servlet if (uri.indexOf("/") == 0) { uri = uri.substring(1); } if (uri.indexOf("/") > -1) { uri = uri.substring(uri.indexOf("/")); } return uri; } }