CommandMap.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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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.
 *
 * @since 1.6
 */
public abstract class CommandMap {
    private static CommandMap defaultCommandMap = null;
    private static Map<ClassLoader,CommandMap> map =
                                new WeakHashMap<ClassLoader,CommandMap>();

    /**
     * Get the default CommandMap.
     * <p>
     *
     * <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).
                if (CommandMap.class.getClassLoader() == null ||
                    CommandMap.class.getClassLoader() !=
                            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;
    }
}