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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.
 */
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).
		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;
    }
}
