jul-to-slf4j/src/main/java/org/slf4j/bridge/SLF4JBridgeHandler.java

/**
 * Copyright (c) 2004-2011 QOS.ch
 * All rights reserved.
 *
 * Permission is hereby granted, free  of charge, to any person obtaining
 * a  copy  of this  software  and  associated  documentation files  (the
 * "Software"), to  deal in  the Software without  restriction, including
 * without limitation  the rights to  use, copy, modify,  merge, publish,
 * distribute,  sublicense, and/or sell  copies of  the Software,  and to
 * permit persons to whom the Software  is furnished to do so, subject to
 * the following conditions:
 *
 * The  above  copyright  notice  and  this permission  notice  shall  be
 * included in all copies or substantial portions of the Software.
 *
 * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
 * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
 * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */
package org.slf4j.bridge;

import java.text.MessageFormat;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.LogManager;
import java.util.logging.LogRecord;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.spi.LocationAwareLogger;

// Based on http://jira.qos.ch/browse/SLF4J-30

/**
 * <p>Bridge/route all JUL log records to the SLF4J API.
 * <p>Essentially, the idea is to install on the root logger an instance of
 * <code>SLF4JBridgeHandler</code> as the sole JUL handler in the system. Subsequently, the
 * SLF4JBridgeHandler instance will redirect all JUL log records are redirected
 * to the SLF4J API based on the following mapping of levels:
 * 
 * <pre>
 * FINEST  -&gt; TRACE
 * FINER   -&gt; DEBUG
 * FINE    -&gt; DEBUG
 * INFO    -&gt; INFO
 * WARNING -&gt; WARN
 * SEVERE  -&gt; ERROR</pre>
 * <p><b>Programmatic installation:</b>
 * <pre>
 * // Optionally remove existing handlers attached to j.u.l root logger
 * SLF4JBridgeHandler.removeHandlersForRootLogger();  // (since SLF4J 1.6.5)

 * // add SLF4JBridgeHandler to j.u.l's root logger, should be done once during
 * // the initialization phase of your application
 * SLF4JBridgeHandler.install();</pre>
 * <p><b>Installation via <em>logging.properties</em> configuration file:</b>
 * <pre>
 * // register SLF4JBridgeHandler as handler for the j.u.l. root logger
 * handlers = org.slf4j.bridge.SLF4JBridgeHandler</pre>
 * <p>Once SLF4JBridgeHandler is installed, logging by j.u.l. loggers will be directed to
 * SLF4J. Example: 
 * <pre>
 * import  java.util.logging.Logger;
 * ...
 * // usual pattern: get a Logger and then log a message
 * Logger julLogger = Logger.getLogger(&quot;org.wombat&quot;);
 * julLogger.fine(&quot;hello world&quot;); // this will get redirected to SLF4J</pre>
 *
 * <p>Please note that translating a java.util.logging event into SLF4J incurs the
 * cost of constructing {@link LogRecord} instance regardless of whether the
 * SLF4J logger is disabled for the given level. <b>Consequently, j.u.l. to
 * SLF4J translation can seriously increase the cost of disabled logging
 * statements (60 fold or 6000% increase) and measurably impact the performance of enabled log
 * statements (20% overall increase).</b> Please note that as of logback-version 0.9.25,
 * it is possible to completely eliminate the 60-fold translation overhead for disabled
 * log statements with the help of <a href="http://logback.qos.ch/manual/configuration.html#LevelChangePropagator">LevelChangePropagator</a>.
 * 
 *
 * <p>If you are concerned about application performance, then use of <code>SLF4JBridgeHandler</code>
 * is appropriate only if any of the following conditions is true:
 * <ol>
 * <li>few j.u.l. logging statements are in play</li>
 * <li>LevelChangePropagator has been installed</li>
 * </ol>
 *
 * <h2>As a Java 9/Jigsaw module</h2>
 * 
 * <p>Given that <b>to</b> is a reserved keyword under Java 9 within module productions, 
 * the MANIFEST.MF file in <em>jul-to-slf4j.jar</em> declares <b>jul_to_slf4j</b> as
 * its Automatic Module Name. Thus, if your application is Jigsaw modularized, the requires 
 * statement in your <em>module-info.java</em> needs to be <b>jul_to_slf4j</b> 
 * (note the two underscores).
 *
 * 
 * @author Christian Stein
 * @author Joern Huxhorn
 * @author Ceki G&uuml;lc&uuml;
 * @author Darryl Smith
 * @since 1.5.1
 */
public class SLF4JBridgeHandler extends Handler {

    // The caller is java.util.logging.Logger
    private static final String FQCN = java.util.logging.Logger.class.getName();
    private static final String UNKNOWN_LOGGER_NAME = "unknown.jul.logger";

    private static final int TRACE_LEVEL_THRESHOLD = Level.FINEST.intValue();
    private static final int DEBUG_LEVEL_THRESHOLD = Level.FINE.intValue();
    private static final int INFO_LEVEL_THRESHOLD = Level.INFO.intValue();
    private static final int WARN_LEVEL_THRESHOLD = Level.WARNING.intValue();

    /**
     * Adds a SLF4JBridgeHandler instance to jul's root logger.
     * 
     * <p>This handler will redirect j.u.l. logging to SLF4J. However, only logs enabled
     * in j.u.l. will be redirected. For example, if a log statement invoking a
     * j.u.l. logger is disabled, then the corresponding non-event will <em>not</em>
     * reach SLF4JBridgeHandler and cannot be redirected.
     */
    public static void install() {
        LogManager.getLogManager().getLogger("").addHandler(new SLF4JBridgeHandler());
    }

    private static java.util.logging.Logger getRootLogger() {
        return LogManager.getLogManager().getLogger("");
    }

    /**
     * Removes previously installed SLF4JBridgeHandler instances. See also
     * {@link #install()}.
     *
     * @throws SecurityException A <code>SecurityException</code> is thrown, if a security manager
     *                           exists and if the caller does not have
     *                           LoggingPermission("control").
     */
    public static void uninstall() throws SecurityException {
        java.util.logging.Logger rootLogger = getRootLogger();
        Handler[] handlers = rootLogger.getHandlers();
        for (Handler handler : handlers) {
            if (handler instanceof SLF4JBridgeHandler) {
                rootLogger.removeHandler(handler);
            }
        }
    }

    /**
     * Returns true if SLF4JBridgeHandler has been previously installed, returns false otherwise.
     *
     * @return true if SLF4JBridgeHandler is already installed, false otherwise
     *
     */
    public static boolean isInstalled() {
        java.util.logging.Logger rootLogger = getRootLogger();
        Handler[] handlers = rootLogger.getHandlers();
        for (Handler handler : handlers) {
            if (handler instanceof SLF4JBridgeHandler) {
                return true;
            }
        }
        return false;
    }

    /**
     * Invoking this method removes/unregisters/detaches all handlers currently attached to the root logger
     * @since 1.6.5
     */
    public static void removeHandlersForRootLogger() {
        java.util.logging.Logger rootLogger = getRootLogger();
        java.util.logging.Handler[] handlers = rootLogger.getHandlers();
        for (Handler handler : handlers) {
            rootLogger.removeHandler(handler);
        }
    }

    /**
     * Initialize this handler.
     */
    public SLF4JBridgeHandler() {
    }

    /**
     * No-op implementation.
     */
    public void close() {
        // empty
    }

    /**
     * No-op implementation.
     */
    public void flush() {
        // empty
    }

    /**
     * Return the Logger instance that will be used for logging.
     * 
     * @param record a LogRecord
     * @return an SLF4J logger corresponding to the record parameter's logger name
     */
    protected Logger getSLF4JLogger(LogRecord record) {
        String name = record.getLoggerName();
        if (name == null) {
            name = UNKNOWN_LOGGER_NAME;
        }
        return LoggerFactory.getLogger(name);
    }

    protected void callLocationAwareLogger(LocationAwareLogger lal, LogRecord record) {
        int julLevelValue = record.getLevel().intValue();
        int slf4jLevel;

        if (julLevelValue <= TRACE_LEVEL_THRESHOLD) {
            slf4jLevel = LocationAwareLogger.TRACE_INT;
        } else if (julLevelValue <= DEBUG_LEVEL_THRESHOLD) {
            slf4jLevel = LocationAwareLogger.DEBUG_INT;
        } else if (julLevelValue <= INFO_LEVEL_THRESHOLD) {
            slf4jLevel = LocationAwareLogger.INFO_INT;
        } else if (julLevelValue <= WARN_LEVEL_THRESHOLD) {
            slf4jLevel = LocationAwareLogger.WARN_INT;
        } else {
            slf4jLevel = LocationAwareLogger.ERROR_INT;
        }
        String i18nMessage = getMessageI18N(record);
        lal.log(null, FQCN, slf4jLevel, i18nMessage, null, record.getThrown());
    }

    protected void callPlainSLF4JLogger(Logger slf4jLogger, LogRecord record) {
        String i18nMessage = getMessageI18N(record);
        int julLevelValue = record.getLevel().intValue();
        if (julLevelValue <= TRACE_LEVEL_THRESHOLD) {
            slf4jLogger.trace(i18nMessage, record.getThrown());
        } else if (julLevelValue <= DEBUG_LEVEL_THRESHOLD) {
            slf4jLogger.debug(i18nMessage, record.getThrown());
        } else if (julLevelValue <= INFO_LEVEL_THRESHOLD) {
            slf4jLogger.info(i18nMessage, record.getThrown());
        } else if (julLevelValue <= WARN_LEVEL_THRESHOLD) {
            slf4jLogger.warn(i18nMessage, record.getThrown());
        } else {
            slf4jLogger.error(i18nMessage, record.getThrown());
        }
    }

    /**
     * Get the record's message, possibly via a resource bundle.
     *
     * @param record
     * @return
     */
    private String getMessageI18N(LogRecord record) {
        String message = record.getMessage();

        if (message == null) {
            return null;
        }

        ResourceBundle bundle = record.getResourceBundle();
        if (bundle != null) {
            try {
                message = bundle.getString(message);
            } catch (MissingResourceException e) {
            }
        }
        Object[] params = record.getParameters();
        // avoid formatting when there are no or 0 parameters. see also
        // http://jira.qos.ch/browse/SLF4J-203
        if (params != null && params.length > 0) {
            try {
                message = MessageFormat.format(message, params);
            } catch (IllegalArgumentException e) {
                // default to the same behavior as in java.util.logging.Formatter.formatMessage(LogRecord)
                // see also http://jira.qos.ch/browse/SLF4J-337
                return message;
            }
        }
        return message;
    }

    /**
     * Publish a LogRecord.
     * <p>
     * The logging request was made initially to a Logger object, which
     * initialized the LogRecord and forwarded it here.
     * <p>
     * This handler ignores the Level attached to the LogRecord, as SLF4J cares
     * about discarding log statements.
     *
     * @param record Description of the log event. A null record is silently ignored
     *               and is not published.
     */
    public void publish(LogRecord record) {
        // Silently ignore null records.
        if (record == null) {
            return;
        }

        Logger slf4jLogger = getSLF4JLogger(record);
        // this is a check to avoid calling the underlying logging system
        // with a null message. While it is legitimate to invoke j.u.l. with
        // a null message, other logging frameworks do not support this.
        // see also http://jira.qos.ch/browse/SLF4J-99
        if (record.getMessage() == null) {
            record.setMessage("");
        }
        if (slf4jLogger instanceof LocationAwareLogger) {
            callLocationAwareLogger((LocationAwareLogger) slf4jLogger, record);
        } else {
            callPlainSLF4JLogger(slf4jLogger, record);
        }
    }

}