handler.java

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/*
 * @(#)Handler.java	1.13 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */


package java.util.logging;

/**
 * A <tt>Handler</tt> object takes log messages from a <tt>Logger</tt> and
 * exports them.  It might for example, write them to a console
 * or write them to a file, or send them to a network logging service,
 * or forward them to an OS log, or whatever.
 * <p>
 * A <tt>Handler</tt> can be disabled by doing a <tt>setLevel(Level.OFF)</tt>
 * and can  be re-enabled by doing a <tt>setLevel</tt> with an appropriate level.
 * <p>
 * <tt>Handler</tt> classes typically use <tt>LogManager</tt> properties to set
 * default values for the <tt>Handler</tt>'s <tt>Filter</tt>, <tt>Formatter</tt>,
 * and <tt>Level</tt>.  See the specific documentation for each concrete
 * <tt>Handler</tt> class.
 *
 *
 * @version 1.13, 01/23/03
 * @since 1.4
 */

public abstract class Handler {
    private static final int offValue = Level.OFF.intValue();
    private LogManager manager = LogManager.getLogManager();
    private Filter filter;
    private Formatter formatter;
    private Level logLevel = Level.ALL;
    private ErrorManager errorManager = new ErrorManager();
    private String encoding;

    // Package private support for security checking.  When sealed
    // is true, we access check updates to the class.
    boolean sealed = true;

    /**
     * Default constructor.  The resulting <tt>Handler</tt> has a log
     * level of <tt>Level.ALL</tt>, no <tt>Formatter</tt>, and no 
     * <tt>Filter</tt>.  A default <tt>ErrorManager</tt> instance is installed
     * as the <tt>ErrorManager</tt>.
     */
    protected Handler() {
    }

    /**
     * Publish a <tt>LogRecord</tt>.
     * <p>
     * The logging request was made initially to a <tt>Logger</tt> object,
     * which initialized the <tt>LogRecord</tt> and forwarded it here.
     * <p>
     * The <tt>Handler</tt>  is responsible for formatting the message, when and
     * if necessary.  The formatting should include localization.
     *
     * @param  record  description of the log event
     */
    public abstract void publish(LogRecord record);

    /**
     * Flush any buffered output.
     */
    public abstract void flush();

    /**
     * Close the <tt>Handler</tt> and free all associated resources.
     * <p>
     * The close method will perform a <tt>flush</tt> and then close the
     * <tt>Handler</tt>.   After close has been called this <tt>Handler</tt>
     * should no longer be used.  Method calls may either be silently
     * ignored or may throw runtime exceptions.
     *
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public abstract void close() throws SecurityException;

    /**
     * Set a <tt>Formatter</tt>.  This <tt>Formatter</tt> will be used 
     * to format <tt>LogRecords</tt> for this <tt>Handler</tt>.
     * <p>
     * Some <tt>Handlers</tt> may not use <tt>Formatters</tt>, in 
     * which case the <tt>Formatter</tt> will be remembered, but not used.
     * <p>
     * @param newFormatter the <tt>Formatter</tt> to use (may not be null)
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public void setFormatter(Formatter newFormatter) throws SecurityException {
	checkAccess();
	// Check for a null pointer:
	newFormatter.getClass();
	formatter = newFormatter;
    }

    /**
     * Return the <tt>Formatter</tt> for this <tt>Handler</tt>.
     * @return the <tt>Formatter</tt> (may be null).
     */
    public Formatter getFormatter() {
	return formatter;
    }

    /**
     * Set the character encoding used by this <tt>Handler</tt>.
     * <p>
     * The encoding should be set before any <tt>LogRecords</tt> are written
     * to the <tt>Handler</tt>.
     *
     * @param encoding  The name of a supported character encoding.
     *	      May be null, to indicate the default platform encoding.
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     * @exception  UnsupportedEncodingException if the named encoding is
     *		not supported.
     */
    public void setEncoding(String encoding) 
			throws SecurityException, java.io.UnsupportedEncodingException {
	checkAccess();
	if (encoding != null) {
	    // Check the encoding exists.
	    sun.io.CharToByteConverter.getConverter(encoding);
	}
	this.encoding = encoding;
    }

    /**
     * Return the character encoding for this <tt>Handler</tt>.
     *
     * @return  The encoding name.  May be null, which indicates the
     *	    	default encoding should be used.
     */
    public String getEncoding() {
	return encoding;
    }

    /**
     * Set a <tt>Filter</tt> to control output on this <tt>Handler</tt>.
     * <P>
     * For each call of <tt>publish</tt> the <tt>Handler</tt> will call
     * this <tt>Filter</tt> (if it is non-null) to check if the
     * <tt>LogRecord</tt> should be published or discarded.
     *
     * @param   newFilter  a <tt>Filter</tt> object (may be null)
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public void setFilter(Filter newFilter) throws SecurityException {
	checkAccess();
	filter = newFilter;
    }

    /**
     * Get the current <tt>Filter</tt> for this <tt>Handler</tt>.
     *
     * @return  a </tt>Filter</tt> object (may be null)
     */
    public Filter getFilter() {
	return filter;
    }

    /**
     * Define an ErrorManager for this Handler.
     * <p>
     * The ErrorManager's "error" method will be invoked if any
     * errors occur while using this Handler.
     *
     * @param em  the new ErrorManager
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public void setErrorManager(ErrorManager em) {
	checkAccess();
	if (em == null) {
	   throw new NullPointerException();
	}
	errorManager = em;
    }
 
    /**
     * Retrieves the ErrorManager for this Handler.
     *
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public ErrorManager getErrorManager() {
	checkAccess();
	return errorManager;
    }

   /**
     * Protected convenience method to report an error to this Handler's
     * ErrorManager.  Note that this method retrieves and uses the ErrorManager
     * without doing a security check.  It can therefore be used in
     * environments where the caller may be non-privileged.
     *
     * @param msg    a descriptive string (may be null)
     * @param ex     an exception (may be null)
     * @param code   an error code defined in ErrorManager
     */
    protected void reportError(String msg, Exception ex, int code) {
	try {
	    errorManager.error(msg, ex, code);
	} catch (Exception ex2) {
	    System.err.println("Handler.reportError caught:");	
	    ex2.printStackTrace();
	}
    }

    /**
     * Set the log level specifying which message levels will be
     * logged by this <tt>Handler</tt>.  Message levels lower than this
     * value will be discarded. 
     * <p>
     * The intention is to allow developers to turn on voluminous
     * logging, but to limit the messages that are sent to certain
     * <tt>Handlers</tt>.
     * 
     * @param newLevel   the new value for the log level
     * @exception  SecurityException  if a security manager exists and if
     *             the caller does not have <tt>LoggingPermission("control")</tt>.
     */
    public synchronized void setLevel(Level newLevel) throws SecurityException {
	if (newLevel == null) {
	    throw new NullPointerException();
	}
	checkAccess();
	logLevel = newLevel;
    }

    /**
     * Get the log level specifying which messages will be
     * logged by this <tt>Handler</tt>.  Message levels lower
     * than this level will be discarded.
     * @return	the level of messages being logged.
     */
    public synchronized Level getLevel() {
	return logLevel;
    }

    /**
     * Check if this <tt>Handler</tt> would actually log a given <tt>LogRecord</tt>.
     * <p>
     * This method checks if the <tt>LogRecord</tt> has an appropriate 
     * <tt>Level</tt> and  whether it satisfies any <tt>Filter</tt>.  It also
     * may make other <tt>Handler</tt> specific checks that might prevent a
     * handler from logging the <tt>LogRecord</tt>.
     * <p>
     * @param record  a <tt>LogRecord</tt>
     * @return true if the <tt>LogRecord</tt> would be logged.
     *
     */
    public boolean isLoggable(LogRecord record) {
	int levelValue = getLevel().intValue();
	if (record.getLevel().intValue() < levelValue || levelValue == offValue) {
	    return false;
	}
	Filter filter = getFilter();
	if (filter == null) {	
	    return true;
	}
	return filter.isLoggable(record);
    }

    // Package-private support method for security checks.
    // If "sealed" is true, we check that the caller has
    // appropriate security privileges to update Handler
    // state and if not throw a SeucirtyException.
    void checkAccess() throws SecurityException {
	if (sealed) {
	    manager.checkAccess();
	}
    }
}