Java tutorial
/* * Copyright 1999-2002,2004 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. * * $Id: ApplicationListener.java 372087 2006-01-25 03:38:42Z craigmcc $ */ import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.struts.apps.mailreader.dao.impl.memory.MemoryUserDatabase; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import java.io.*; /** * <p><code>ServletContextListener</code> that initializes and finalizes the * persistent storage of User and Subscription information for the Struts * Demonstration Application, using an in-memory database backed by an XML * file.</p> * <p/> * <p><strong>IMPLEMENTATION WARNING</strong> - If this web application is run * from a WAR file, or in another environment where reading and writing of the * web application resource is impossible, the initial contents will be copied * to a file in the web application temporary directory provided by the * container. This is for demonstration purposes only - you should * <strong>NOT</strong> assume that files written here will survive a restart * of your servlet container.</p> * <p/> * <p>This class was borrowed from the Shale Mailreader. Changes were:</p> * <p/> * <ul> * <p/> * <li>Path to database.xml (under classes here). </li> * <p/> * <li>Class to store protocol list (an array here). </li> * <p/> * </ul> * <p/> * DEVELOPMENT NOTE - Another approach would be to instantiate the database via Spring. * </p> */ public final class DatabaseListener implements ServletContextListener { // ------------------------------------------------------ Manifest Constants /** * <p>Appication scope attribute key under which the in-memory version of * our database is stored.</p> */ public static final String DATABASE_KEY = "database"; /** * <p>Application scope attribute key under which the valid selection * items for the protocol property is stored.</p> */ public static final String PROTOCOLS_KEY = "protocols"; // ------------------------------------------------------ Instance Variables /** * <p>The <code>ServletContext</code> for this web application.</p> */ private ServletContext context = null; /** * The {@link MemoryUserDatabase} object we construct and make available. */ private MemoryUserDatabase database = null; /** * <p>Logging output for this plug in instance.</p> */ private Log log = LogFactory.getLog(this.getClass()); // ------------------------------------------------------------- Properties /** * <p>The web application resource path of our persistent database storage * file.</p> */ private String pathname = "/WEB-INF/classes/database.xml"; /** * <p>Return the application resource path to the database.</p> * * @return application resource path path to the database */ public String getPathname() { return (this.pathname); } /** * <p>Set the application resource path to the database.</p> * * @param pathname to the database */ public void setPathname(String pathname) { this.pathname = pathname; } // ------------------------------------------ ServletContextListener Methods /** * <p>Gracefully shut down this database, releasing any resources that * were allocated at initialization.</p> * * @param event ServletContextEvent to process */ public void contextDestroyed(ServletContextEvent event) { log.info("Finalizing memory database plug in"); if (database != null) { try { database.close(); } catch (Exception e) { log.error("Closing memory database", e); } } context.removeAttribute(DATABASE_KEY); context.removeAttribute(PROTOCOLS_KEY); database = null; context = null; } /** * <p>Initialize and load our initial database from persistent * storage.</p> * * @param event The context initialization event */ public void contextInitialized(ServletContextEvent event) { log.info("Initializing memory database plug in from '" + pathname + "'"); // Remember our associated ServletContext this.context = event.getServletContext(); // Construct a new database and make it available database = new MemoryUserDatabase(); try { String path = calculatePath(); if (log.isDebugEnabled()) { log.debug(" Loading database from '" + path + "'"); } database.setPathname(path); database.open(); } catch (Exception e) { log.error("Opening memory database", e); throw new IllegalStateException("Cannot load database from '" + pathname + "': " + e); } context.setAttribute(DATABASE_KEY, database); } // -------------------------------------------------------- Private Methods /** * <p>Calculate and return an absolute pathname to the XML file to contain * our persistent storage information.</p> * * @return Absolute path to XML file. * @throws Exception if an input/output error occurs */ private String calculatePath() throws Exception { // Can we access the database via file I/O? String path = context.getRealPath(pathname); if (path != null) { return (path); } // Does a copy of this file already exist in our temporary directory File dir = (File) context.getAttribute("javax.servlet.context.tempdir"); File file = new File(dir, "struts-example-database.xml"); if (file.exists()) { return (file.getAbsolutePath()); } // Copy the static resource to a temporary file and return its path InputStream is = context.getResourceAsStream(pathname); BufferedInputStream bis = new BufferedInputStream(is, 1024); FileOutputStream os = new FileOutputStream(file); BufferedOutputStream bos = new BufferedOutputStream(os, 1024); byte buffer[] = new byte[1024]; while (true) { int n = bis.read(buffer); if (n <= 0) { break; } bos.write(buffer, 0, n); } bos.close(); bis.close(); return (file.getAbsolutePath()); } }