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. */ package org.apache.struts.webapp.example2.memory; import java.io.BufferedInputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.util.HashMap; import org.apache.commons.digester.Digester; import org.apache.commons.digester.ObjectCreationFactory; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.struts.webapp.example2.Subscription; import org.apache.struts.webapp.example2.User; import org.apache.struts.webapp.example2.UserDatabase; import org.xml.sax.Attributes; /** * <p>Concrete implementation of {@link UserDatabase} for an in-memory * database backed by an XML data file.</p> * * @author Craig R. McClanahan * @version $Rev: 54934 $ $Date: 2004-10-16 18:07:50 +0100 (Sat, 16 Oct 2004) $ * @since Struts 1.1 */ public final class MemoryUserDatabase implements UserDatabase { // ----------------------------------------------------------- Constructors // ----------------------------------------------------- Instance Variables /** * Logging output for this user database instance. */ private Log log = LogFactory.getLog(this.getClass()); /** * The {@link User}s associated with this UserDatabase, keyed by username. */ private HashMap users = new HashMap(); // ------------------------------------------------------------- Properties /** * Absolute pathname to the persistent file we use for loading and storing * persistent data. */ private String pathname = null; private String pathnameOld = null; private String pathnameNew = null; public String getPathname() { return (this.pathname); } public void setPathname(String pathname) { this.pathname = pathname; pathnameOld = pathname + ".old"; pathnameNew = pathname + ".new"; } // --------------------------------------------------------- Public Methods /** * <p>Finalize access to the underlying persistence layer.</p> * * @exception Exception if a database access error occurs */ public void close() throws Exception { save(); } /** * <p>Create and return a new {@link User} defined in this user database. * </p> * * @param username Username of the new user * * @exception IllegalArgumentExceptionif the specified username * is not unique */ public User createUser(String username) { synchronized (users) { if (users.get(username) != null) { throw new IllegalArgumentException("Duplicate user '" + username + "'"); } if (log.isTraceEnabled()) { log.trace("Creating user '" + username + "'"); } MemoryUser user = new MemoryUser(this, username); synchronized (users) { users.put(username, user); } return (user); } } /** * <p>Return the existing {@link User} with the specified username, * if any; otherwise return <code>null</code>.</p> * * @param username Username of the user to retrieve */ public User findUser(String username) { synchronized (users) { return ((User) users.get(username)); } } /** * <p>Return the set of {@link User}s defined in this user database.</p> */ public User[] findUsers() { synchronized (users) { User results[] = new User[users.size()]; return ((User[]) users.values().toArray(results)); } } /** * <p>Initiate access to the underlying persistence layer.</p> * * @exception Exception if a database access error occurs */ public void open() throws Exception { FileInputStream fis = null; BufferedInputStream bis = null; try { // Acquire an input stream to our database file if (log.isDebugEnabled()) { log.debug("Loading database from '" + pathname + "'"); } fis = new FileInputStream(pathname); bis = new BufferedInputStream(fis); // Construct a digester to use for parsing Digester digester = new Digester(); digester.push(this); digester.setValidating(false); digester.addFactoryCreate("database/user", new MemoryUserCreationFactory(this)); digester.addFactoryCreate("database/user/subscription", new MemorySubscriptionCreationFactory(this)); // Parse the input stream to initialize our database digester.parse(bis); bis.close(); bis = null; fis = null; } catch (Exception e) { log.error("Loading database from '" + pathname + "':", e); throw e; } finally { if (bis != null) { try { bis.close(); } catch (Throwable t) { ; } bis = null; fis = null; } } } /** * Remove the specified {@link User} from this database. * * @param user User to be removed * * @exception IllegalArgumentException if the specified user is not * associated with this database */ public void removeUser(User user) { if (!(this == user.getDatabase())) { throw new IllegalArgumentException("User not associated with this database"); } if (log.isTraceEnabled()) { log.trace("Removing user '" + user.getUsername() + "'"); } synchronized (users) { users.remove(user.getUsername()); } } /** * <p>Save any pending changes to the underlying persistence layer.</p> * * @exception Exception if a database access error occurs */ public void save() throws Exception { if (log.isDebugEnabled()) { log.debug("Saving database to '" + pathname + "'"); } File fileNew = new File(pathnameNew); PrintWriter writer = null; try { // Configure our PrintWriter FileOutputStream fos = new FileOutputStream(fileNew); OutputStreamWriter osw = new OutputStreamWriter(fos); writer = new PrintWriter(osw); // Print the file prolog writer.println("<?xml version='1.0'?>"); writer.println("<database>"); // Print entries for each defined user and associated subscriptions User users[] = findUsers(); for (int i = 0; i < users.length; i++) { writer.print(" "); writer.println(users[i]); Subscription subscriptions[] = users[i].getSubscriptions(); for (int j = 0; j < subscriptions.length; j++) { writer.print(" "); writer.println(subscriptions[j]); writer.print(" "); writer.println("</subscription>"); } writer.print(" "); writer.println("</user>"); } // Print the file epilog writer.println("</database>"); // Check for errors that occurred while printing if (writer.checkError()) { writer.close(); fileNew.delete(); throw new IOException("Saving database to '" + pathname + "'"); } writer.close(); writer = null; } catch (IOException e) { if (writer != null) { writer.close(); } fileNew.delete(); throw e; } // Perform the required renames to permanently save this file File fileOrig = new File(pathname); File fileOld = new File(pathnameOld); if (fileOrig.exists()) { fileOld.delete(); if (!fileOrig.renameTo(fileOld)) { throw new IOException("Renaming '" + pathname + "' to '" + pathnameOld + "'"); } } if (!fileNew.renameTo(fileOrig)) { if (fileOld.exists()) { fileOld.renameTo(fileOrig); } throw new IOException("Renaming '" + pathnameNew + "' to '" + pathname + "'"); } fileOld.delete(); } } /** * Digester object creation factory for subscription instances. */ class MemorySubscriptionCreationFactory implements ObjectCreationFactory { public MemorySubscriptionCreationFactory(MemoryUserDatabase database) { this.database = database; } private MemoryUserDatabase database = null; private Digester digester = null; public Digester getDigester() { return (this.digester); } public void setDigester(Digester digester) { this.digester = digester; } public Object createObject(Attributes attributes) { String host = attributes.getValue("host"); User user = (User) digester.peek(); Subscription subscription = user.createSubscription(host); String autoConnect = attributes.getValue("autoConnect"); if (autoConnect == null) { autoConnect = "false"; } if ("true".equalsIgnoreCase(autoConnect) || "yes".equalsIgnoreCase(autoConnect)) { subscription.setAutoConnect(true); } else { subscription.setAutoConnect(false); } subscription.setPassword(attributes.getValue("password")); subscription.setType(attributes.getValue("type")); subscription.setUsername(attributes.getValue("username")); return (subscription); } } /** * Digester object creation factory for user instances. */ class MemoryUserCreationFactory implements ObjectCreationFactory { public MemoryUserCreationFactory(MemoryUserDatabase database) { this.database = database; } private MemoryUserDatabase database = null; private Digester digester = null; public Digester getDigester() { return (this.digester); } public void setDigester(Digester digester) { this.digester = digester; } public Object createObject(Attributes attributes) { String username = attributes.getValue("username"); User user = database.createUser(username); user.setFromAddress(attributes.getValue("fromAddress")); user.setFullName(attributes.getValue("fullName")); user.setPassword(attributes.getValue("password")); user.setReplyToAddress(attributes.getValue("replyToAddress")); return (user); } }