Class SLF4JBridgeHandler

  • public class SLF4JBridgeHandler
    extends Handler

    Bridge/route all JUL log records to the SLF4J API.

    Essentially, the idea is to install on the root logger an instance of SLF4JBridgeHandler 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:

     FINER   -> DEBUG
     FINE    -> DEBUG
     INFO    -> INFO

    Programmatic installation:

     // 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

    Installation via configuration file:

     // register SLF4JBridgeHandler as handler for the j.u.l. root logger
     handlers = org.slf4j.bridge.SLF4JBridgeHandler

    Once SLF4JBridgeHandler is installed, logging by j.u.l. loggers will be directed to SLF4J. Example:

     import  java.util.logging.Logger;
     // usual pattern: get a Logger and then log a message
     Logger julLogger = Logger.getLogger("org.wombat");
     julLogger.fine("hello world"); // this will get redirected to SLF4J

    Please note that translating a java.util.logging event into SLF4J incurs the cost of constructing LogRecord instance regardless of whether the SLF4J logger is disabled for the given level. 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). 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 LevelChangePropagator.

    If you are concerned about application performance, then use of SLF4JBridgeHandler is appropriate only if any one the following two conditions is true:

    1. few j.u.l. logging statements are in play
    2. LevelChangePropagator has been installed

    As a Java 9/Jigsaw module

    Given that to is a reserved keyword under Java 9 within module productions, the MAFIFEST.MF file in jul-to-slf4j.jar declares jul_to_slf4j as its Automatic Module Name. Thus, if your application is Jigsaw modularized, the requires statement in your needs to be jul_to_slf4j (note the two underscores).

    Christian Stein, Joern Huxhorn, Ceki Gülcü, Darryl Smith
    • Method Detail

      • install

        public static void install()
        Adds a SLF4JBridgeHandler instance to jul's root logger.

        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 not reach SLF4JBridgeHandler and cannot be redirected.

      • uninstall

        public static void uninstall()
                              throws SecurityException
        Removes previously installed SLF4JBridgeHandler instances. See also install().
        SecurityException - A SecurityException is thrown, if a security manager exists and if the caller does not have LoggingPermission("control").
      • isInstalled

        public static boolean isInstalled()
        Returns true if SLF4JBridgeHandler has been previously installed, returns false otherwise.
        true if SLF4JBridgeHandler is already installed, false other wise
      • removeHandlersForRootLogger

        public static void removeHandlersForRootLogger()
        Invoking this method removes/unregisters/detaches all handlers currently attached to the root logger
      • close

        public void close()
        No-op implementation.
        Specified by:
        close in class Handler
      • flush

        public void flush()
        No-op implementation.
        Specified by:
        flush in class Handler
      • getSLF4JLogger

        protected Logger getSLF4JLogger​(LogRecord record)
        Return the Logger instance that will be used for logging.
        record - a LogRecord
        an SLF4J logger corresponding to the record parameter's logger name
      • publish

        public void publish​(LogRecord record)
        Publish a LogRecord.

        The logging request was made initially to a Logger object, which initialized the LogRecord and forwarded it here.

        This handler ignores the Level attached to the LogRecord, as SLF4J cares about discarding log statements.

        Specified by:
        publish in class Handler
        record - Description of the log event. A null record is silently ignored and is not published.