org.apache.logging.log4j.jul

Class Log4jBridgeHandler

  • All Implemented Interfaces:
    PropertyChangeListener, EventListener

    public class Log4jBridgeHandler
extends Handler
implements PropertyChangeListener
    Bridge from JUL to log4j2.
    This is an alternative to log4j.jul.LogManager (running as complete JUL replacement), especially useful for webapps running on a container for which the LogManager cannot or should not be used.

    Installation/usage:
    • Declaratively inside JUL's logging.properties:
      handlers = org.apache.logging.log4j.jul.Log4jBridgeHandler
      (and typically also:   org.apache.logging.log4j.jul.Log4jBridgeHandler.propagateLevels = true )
      Note: in a webapp running on Tomcat, you may create a WEB-INF/classes/logging.properties file to configure JUL for this webapp only: configured handlers and log levels affect your webapp only! This file is then the complete JUL configuration, so JUL's defaults (e.g. log level INFO) apply for stuff not explicitly defined therein.
    • Programmatically by calling install() method, e.g. inside ServletContextListener static-class-init. or contextInitialized()
    Configuration (in JUL's logging.properties):
    • Log4jBridgeHandler.suffixToAppend
      String, suffix to append to JUL logger names, to easily recognize bridged log messages. A dot "." is automatically prepended, so configuration for the basis logger is used
      Example: Log4jBridgeHandler.suffixToAppend = _JUL
      Useful, for example, if you use JSF because it logs exceptions and throws them afterwards; you can easily recognize the duplicates with this (or concentrate on the non-JUL-logs).
    • Log4jBridgeHandler.propagateLevels   boolean, "true" to automatically propagate log4j log levels to JUL.
    • Log4jBridgeHandler.sysoutDebug   boolean, perform some (developer) debug output to sysout
    Log levels are translated with LevelTranslator, see also log4j doc.

    Restrictions:
    • Manually given source/location info in JUL (e.g. entering(), exiting(), throwing(), logp(), logrb() ) will NOT be considered, i.e. gets lost in log4j logging.
    • Log levels of JUL have to be adjusted according to log4j log levels: Either by using "propagateLevels" (preferred), or manually by specifying them explicitly, i.e. logging.properties and log4j2.xml have some redundancies.
    • Only JUL log events that are allowed according to the JUL log level get to this handler and thus to log4j. This is only relevant and important if you NOT use "propagateLevels". If you set .level = SEVERE only error logs will be seen by this handler and thus log4j - even if the corresponding log4j log level is ALL.
      On the other side, you should NOT set .level = FINER or FINEST if the log4j level is higher. In this case a lot of JUL log events would be generated, sent via this bridge to log4j and thrown away by the latter.
      Note: JUL's default log level (i.e. none specified in logger.properties) is INFO.
    (Credits: idea and concept originate from org.slf4j.bridge.SLF4JBridgeHandler; level propagation idea originates from logback/LevelChangePropagator; but no source code has been copied)

    • Constructor Detail

      • Log4jBridgeHandler

        public Log4jBridgeHandler()
        Initialize this handler by reading out JUL configuration.

      • Log4jBridgeHandler

        public Log4jBridgeHandler(boolean debugOutput,
                          String suffixToAppend,
                          boolean propagateLevels)
        Initialize this handler with given configuration.

    • Method Detail

      • install

        public static void install(boolean removeHandlersForRootLogger,
                           String suffixToAppend,
                           boolean propagateLevels)
        Adds a new Log4jBridgeHandler instance to JUL's root logger. This is a programmatic alternative to specify handlers = org.apache.logging.log4j.jul.Log4jBridgeHandler and its configuration in logging.properties.
        Parameters:
        removeHandlersForRootLogger - true to remove all other installed handlers on JUL root level

      • init

        protected void init(boolean debugOutput,
                    String suffixToAppend,
                    boolean propagateLevels)
        Perform init. of this handler with given configuration (typical use is for constructor).

      • close

        public void close()
        Specified by:
        close in class Handler

      • flush

        public void flush()
        Specified by:
        flush in class Handler

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