Package org.slf4j.bridge

Class SLF4JBridgeHandler

  • public class SLF4JBridgeHandler
extends java.util.logging.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: 

     FINEST  -> TRACE
 FINER   -> DEBUG
 FINE    -> DEBUG
 INFO    -> INFO
 WARNING -> WARN
 SEVERE  -> ERROR

    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
 SLF4JBridgeHandler.install();

    Installation via logging.properties 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
    Since:
    1.5.1

    • Constructor Summary

      Constructors 
      Constructor Description
      SLF4JBridgeHandler()
      Initialize this handler.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      protected void callLocationAwareLogger​(LocationAwareLogger lal, java.util.logging.LogRecord record)  
      protected void callPlainSLF4JLogger​(Logger slf4jLogger, java.util.logging.LogRecord record)  
      void close()
      No-op implementation.
      void flush()
      No-op implementation.
      private java.lang.String getMessageI18N​(java.util.logging.LogRecord record)
      Get the record's message, possibly via a resource bundle.
      private static java.util.logging.Logger getRootLogger()  
      protected Logger getSLF4JLogger​(java.util.logging.LogRecord record)
      Return the Logger instance that will be used for logging.
      static void install()
      Adds a SLF4JBridgeHandler instance to jul's root logger.
      static boolean isInstalled()
      Returns true if SLF4JBridgeHandler has been previously installed, returns false otherwise.
      void publish​(java.util.logging.LogRecord record)
      Publish a LogRecord.
      static void removeHandlersForRootLogger()
      Invoking this method removes/unregisters/detaches all handlers currently attached to the root logger
      static void uninstall()
      Removes previously installed SLF4JBridgeHandler instances.

      • Methods inherited from class java.util.logging.Handler

        getEncoding, getErrorManager, getFilter, getFormatter, getLevel, isLoggable, reportError, setEncoding, setErrorManager, setFilter, setFormatter, setLevel

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • FQCN

        private static final java.lang.String FQCN

      • UNKNOWN_LOGGER_NAME

        private static final java.lang.String UNKNOWN_LOGGER_NAME
        See Also:
        Constant Field Values

      • TRACE_LEVEL_THRESHOLD

        private static final int TRACE_LEVEL_THRESHOLD

      • DEBUG_LEVEL_THRESHOLD

        private static final int DEBUG_LEVEL_THRESHOLD

      • INFO_LEVEL_THRESHOLD

        private static final int INFO_LEVEL_THRESHOLD

      • WARN_LEVEL_THRESHOLD

        private static final int WARN_LEVEL_THRESHOLD

    • Constructor Detail

      • SLF4JBridgeHandler

        public SLF4JBridgeHandler()
        Initialize this handler.

    • 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.

      • getRootLogger

        private static java.util.logging.Logger getRootLogger()

      • uninstall

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

      • isInstalled

        public static boolean isInstalled()
                           throws java.lang.SecurityException
        Returns true if SLF4JBridgeHandler has been previously installed, returns false otherwise.
        Returns:
        true if SLF4JBridgeHandler is already installed, false other wise
        Throws:
        java.lang.SecurityException

      • removeHandlersForRootLogger

        public static void removeHandlersForRootLogger()
        Invoking this method removes/unregisters/detaches all handlers currently attached to the root logger
        Since:
        1.6.5

      • close

        public void close()
        No-op implementation.
        Specified by:
        close in class java.util.logging.Handler

      • flush

        public void flush()
        No-op implementation.
        Specified by:
        flush in class java.util.logging.Handler

      • getSLF4JLogger

        protected Logger getSLF4JLogger​(java.util.logging.LogRecord record)
        Return the Logger instance that will be used for logging.

      • callLocationAwareLogger

        protected void callLocationAwareLogger​(LocationAwareLogger lal,
                                       java.util.logging.LogRecord record)

      • callPlainSLF4JLogger

        protected void callPlainSLF4JLogger​(Logger slf4jLogger,
                                    java.util.logging.LogRecord record)

      • getMessageI18N

        private java.lang.String getMessageI18N​(java.util.logging.LogRecord record)
        Get the record's message, possibly via a resource bundle.
        Parameters:
        record -
        Returns:

      • publish

        public void publish​(java.util.logging.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 java.util.logging.Handler
        Parameters:
        record - Description of the log event. A null record is silently ignored and is not published.