Java tutorial
/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER. * * Copyright (c) 1997-2017 Oracle and/or its affiliates. All rights reserved. * * The contents of this file are subject to the terms of either the GNU * General Public License Version 2 only ("GPL") or the Common Development * and Distribution License("CDDL") (collectively, the "License"). You * may not use this file except in compliance with the License. You can * obtain a copy of the License at * https://oss.oracle.com/licenses/CDDL+GPL-1.1 * or LICENSE.txt. See the License for the specific * language governing permissions and limitations under the License. * * When distributing the software, include this License Header Notice in each * file and include the License file at LICENSE.txt. * * GPL Classpath Exception: * Oracle designates this particular file as subject to the "Classpath" * exception as provided by Oracle in the GPL Version 2 section of the License * file that accompanied this code. * * Modifications: * If applicable, add the following below the License Header, with the fields * enclosed by brackets [] replaced by your own identifying information: * "Portions Copyright [year] [name of copyright owner]" * * Contributor(s): * If you wish your version of this file to be governed by only the CDDL or * only the GPL Version 2, indicate your decision by adding "[Contributor] * elects to include this software in this distribution under the [CDDL or GPL * Version 2] license." If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. */ package javax.activation; import java.util.Map; import java.util.WeakHashMap; /** * The CommandMap class provides an interface to a registry of * command objects available in the system. * Developers are expected to either use the CommandMap * implementation included with this package (MailcapCommandMap) or * develop their own. Note that some of the methods in this class are * abstract. */ public abstract class CommandMap { private static CommandMap defaultCommandMap = null; private static Map<ClassLoader, CommandMap> map = new WeakHashMap<ClassLoader, CommandMap>(); /** * Get the default CommandMap. * * <ul> * <li> In cases where a CommandMap instance has been previously set * to some value (via <i>setDefaultCommandMap</i>) * return the CommandMap. * <li> * In cases where no CommandMap has been set, the CommandMap * creates an instance of <code>MailcapCommandMap</code> and * set that to the default, returning its value. * * </ul> * * @return the CommandMap */ public static synchronized CommandMap getDefaultCommandMap() { if (defaultCommandMap != null) return defaultCommandMap; // fetch per-thread-context-class-loader default ClassLoader tccl = SecuritySupport.getContextClassLoader(); CommandMap def = map.get(tccl); if (def == null) { def = new MailcapCommandMap(); map.put(tccl, def); } return def; } /** * Set the default CommandMap. Reset the CommandMap to the default by * calling this method with <code>null</code>. * * @param commandMap The new default CommandMap. * @exception SecurityException if the caller doesn't have permission * to change the default */ public static synchronized void setDefaultCommandMap(CommandMap commandMap) { SecurityManager security = System.getSecurityManager(); if (security != null) { try { // if it's ok with the SecurityManager, it's ok with me... security.checkSetFactory(); } catch (SecurityException ex) { // otherwise, we also allow it if this code and the // factory come from the same (non-system) class loader (e.g., // the JAF classes were loaded with the applet classes). ClassLoader cl = CommandMap.class.getClassLoader(); if (cl == null || cl.getParent() == null || cl != commandMap.getClass().getClassLoader()) { throw ex; } } } // remove any per-thread-context-class-loader CommandMap map.remove(SecuritySupport.getContextClassLoader()); defaultCommandMap = commandMap; } /** * Get the preferred command list from a MIME Type. The actual semantics * are determined by the implementation of the CommandMap. * * @param mimeType the MIME type * @return the CommandInfo classes that represent the command Beans. */ abstract public CommandInfo[] getPreferredCommands(String mimeType); /** * Get the preferred command list from a MIME Type. The actual semantics * are determined by the implementation of the CommandMap. <p> * * The <code>DataSource</code> provides extra information, such as * the file name, that a CommandMap implementation may use to further * refine the list of commands that are returned. The implementation * in this class simply calls the <code>getPreferredCommands</code> * method that ignores this argument. * * @param mimeType the MIME type * @param ds a DataSource for the data * @return the CommandInfo classes that represent the command Beans. * @since JAF 1.1 */ public CommandInfo[] getPreferredCommands(String mimeType, DataSource ds) { return getPreferredCommands(mimeType); } /** * Get all the available commands for this type. This method * should return all the possible commands for this MIME type. * * @param mimeType the MIME type * @return the CommandInfo objects representing all the commands. */ abstract public CommandInfo[] getAllCommands(String mimeType); /** * Get all the available commands for this type. This method * should return all the possible commands for this MIME type. <p> * * The <code>DataSource</code> provides extra information, such as * the file name, that a CommandMap implementation may use to further * refine the list of commands that are returned. The implementation * in this class simply calls the <code>getAllCommands</code> * method that ignores this argument. * * @param mimeType the MIME type * @param ds a DataSource for the data * @return the CommandInfo objects representing all the commands. * @since JAF 1.1 */ public CommandInfo[] getAllCommands(String mimeType, DataSource ds) { return getAllCommands(mimeType); } /** * Get the default command corresponding to the MIME type. * * @param mimeType the MIME type * @param cmdName the command name * @return the CommandInfo corresponding to the command. */ abstract public CommandInfo getCommand(String mimeType, String cmdName); /** * Get the default command corresponding to the MIME type. <p> * * The <code>DataSource</code> provides extra information, such as * the file name, that a CommandMap implementation may use to further * refine the command that is chosen. The implementation * in this class simply calls the <code>getCommand</code> * method that ignores this argument. * * @param mimeType the MIME type * @param cmdName the command name * @param ds a DataSource for the data * @return the CommandInfo corresponding to the command. * @since JAF 1.1 */ public CommandInfo getCommand(String mimeType, String cmdName, DataSource ds) { return getCommand(mimeType, cmdName); } /** * Locate a DataContentHandler that corresponds to the MIME type. * The mechanism and semantics for determining this are determined * by the implementation of the particular CommandMap. * * @param mimeType the MIME type * @return the DataContentHandler for the MIME type */ abstract public DataContentHandler createDataContentHandler(String mimeType); /** * Locate a DataContentHandler that corresponds to the MIME type. * The mechanism and semantics for determining this are determined * by the implementation of the particular CommandMap. <p> * * The <code>DataSource</code> provides extra information, such as * the file name, that a CommandMap implementation may use to further * refine the choice of DataContentHandler. The implementation * in this class simply calls the <code>createDataContentHandler</code> * method that ignores this argument. * * @param mimeType the MIME type * @param ds a DataSource for the data * @return the DataContentHandler for the MIME type * @since JAF 1.1 */ public DataContentHandler createDataContentHandler(String mimeType, DataSource ds) { return createDataContentHandler(mimeType); } /** * Get all the MIME types known to this command map. * If the command map doesn't support this operation, * null is returned. * * @return array of MIME types as strings, or null if not supported * @since JAF 1.1 */ public String[] getMimeTypes() { return null; } }