Home » openjdk-7 » java » util » logging » [javadoc | source]
java.util.logging
public class: Logger [javadoc | source]
java.lang.Object
   java.util.logging.Logger

Direct Known Subclasses:
    RootLogger

A Logger object is used to log messages for a specific system or application component. Loggers are normally named, using a hierarchical dot-separated namespace. Logger names can be arbitrary strings, but they should normally be based on the package name or class name of the logged component, such as java.net or javax.swing. In addition it is possible to create "anonymous" Loggers that are not stored in the Logger namespace.

Logger objects may be obtained by calls on one of the getLogger factory methods. These will either create a new Logger or return a suitable existing Logger. It is important to note that the Logger returned by one of the {@code getLogger} factory methods may be garbage collected at any time if a strong reference to the Logger is not kept.

Logging messages will be forwarded to registered Handler objects, which can forward the messages to a variety of destinations, including consoles, files, OS logs, etc.

Each Logger keeps track of a "parent" Logger, which is its nearest existing ancestor in the Logger namespace.

Each Logger has a "Level" associated with it. This reflects a minimum Level that this logger cares about. If a Logger's level is set to null, then its effective level is inherited from its parent, which may in turn obtain it recursively from its parent, and so on up the tree.

The log level can be configured based on the properties from the logging configuration file, as described in the description of the LogManager class. However it may also be dynamically changed by calls on the Logger.setLevel method. If a logger's level is changed the change may also affect child loggers, since any child logger that has null as its level will inherit its effective level from its parent.

On each logging call the Logger initially performs a cheap check of the request level (e.g., SEVERE or FINE) against the effective log level of the logger. If the request level is lower than the log level, the logging call returns immediately.

After passing this initial (cheap) test, the Logger will allocate a LogRecord to describe the logging message. It will then call a Filter (if present) to do a more detailed check on whether the record should be published. If that passes it will then publish the LogRecord to its output Handlers. By default, loggers also publish to their parent's Handlers, recursively up the tree.

Each Logger may have a ResourceBundle name associated with it. The named bundle will be used for localizing logging messages. If a Logger does not have its own ResourceBundle name, then it will inherit the ResourceBundle name from its parent, recursively up the tree.

Most of the logger output methods take a "msg" argument. This msg argument may be either a raw value or a localization key. During formatting, if the logger has (or inherits) a localization ResourceBundle and if the ResourceBundle has a mapping for the msg string, then the msg string is replaced by the localized value. Otherwise the original msg string is used. Typically, formatters use java.text.MessageFormat style formatting to format parameters, so for example a format string "{0} {1}" would format two parameters as strings.

When mapping ResourceBundle names to ResourceBundles, the Logger will first try to use the Thread's ContextClassLoader. If that is null it will try the SystemClassLoader instead. As a temporary transition feature in the initial implementation, if the Logger is unable to locate a ResourceBundle from the ContextClassLoader or SystemClassLoader the Logger will also search up the class stack and use successive calling ClassLoaders to try to locate a ResourceBundle. (This call stack search is to allow containers to transition to using ContextClassLoaders and is likely to be removed in future versions.)

Formatting (including localization) is the responsibility of the output Handler, which will typically call a Formatter.

Note that formatting need not occur synchronously. It may be delayed until a LogRecord is actually written to an external sink.

The logging methods are grouped in five main categories:

For the methods that do not take an explicit source name and method name, the Logging framework will make a "best effort" to determine which class and method called into the logging method. However, it is important to realize that this automatically inferred information may only be approximate (or may even be quite wrong!). Virtual machines are allowed to do extensive optimizations when JITing and may entirely remove stack frames, making it impossible to reliably locate the calling class and method.

All methods on Logger are multi-thread safe.

Subclassing Information: Note that a LogManager class may provide its own implementation of named Loggers for any point in the namespace. Therefore, any subclasses of Logger (unless they are implemented in conjunction with a new LogManager class) should take care to obtain a Logger instance from the LogManager class and should delegate operations such as "isLoggable" and "log(LogRecord)" to that instance. Note that in order to intercept all logging output, subclasses need only override the log(LogRecord) method. All the other logging methods are implemented as calls on this log(LogRecord) method.

Field Summary
public static final  String GLOBAL_LOGGER_NAME    GLOBAL_LOGGER_NAME is a name for the global logger.
    since: 1.6 -
 
public static final  Logger global    The "global" Logger object is provided as a convenience to developers who are making casual use of the Logging package. Developers who are making serious use of the logging package (for example in products) should create and use their own Logger objects, with appropriate names, so that logging can be controlled on a suitable per-Logger granularity. Developers also need to keep a strong reference to their Logger objects to prevent them from being garbage collected.

     
    Constructor:
     protected Logger(String name,
        String resourceBundleName) 
      Protected method to construct a logger for a named subsystem.

      The logger will be initially configured with a null Level and with useParentHandlers set to true.

      Parameters:
      name - A name for the logger. This should be a dot-separated name and should normally be based on the package name or class name of the subsystem, such as java.net or javax.swing. It may be null for anonymous Loggers.
      resourceBundleName - name of ResourceBundle to be used for localizing messages for this logger. May be null if none of the messages require localization.
      Throws:
      MissingResourceException - if the resourceBundleName is non-null and no corresponding resource can be found.
    Method from java.util.logging.Logger Summary:
    addHandler,   config,   entering,   entering,   entering,   exiting,   exiting,   fine,   finer,   finest,   getAnonymousLogger,   getAnonymousLogger,   getFilter,   getGlobal,   getHandlers,   getLevel,   getLogger,   getLogger,   getName,   getParent,   getResourceBundle,   getResourceBundleName,   getUseParentHandlers,   info,   isLoggable,   log,   log,   log,   log,   log,   logp,   logp,   logp,   logp,   logrb,   logrb,   logrb,   logrb,   removeChildLogger,   removeHandler,   setFilter,   setLevel,   setLogManager,   setParent,   setUseParentHandlers,   severe,   throwing,   warning
    Methods from java.lang.Object:
    clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
    Method from java.util.logging.Logger Detail:
     public  void addHandler(Handler handler) throws SecurityException 
      Add a log Handler to receive logging messages.

      By default, Loggers also send their output to their parent logger. Typically the root Logger is configured with a set of Handlers that essentially act as default handlers for all loggers.

     public  void config(String msg) 
      Log a CONFIG message.

      If the logger is currently enabled for the CONFIG message level then the given message is forwarded to all the registered output Handler objects.

     public  void entering(String sourceClass,
        String sourceMethod) 
      Log a method entry.

      This is a convenience method that can be used to log entry to a method. A LogRecord with message "ENTRY", log level FINER, and the given sourceMethod and sourceClass is logged.

     public  void entering(String sourceClass,
        String sourceMethod,
        Object param1) 
      Log a method entry, with one parameter.

      This is a convenience method that can be used to log entry to a method. A LogRecord with message "ENTRY {0}", log level FINER, and the given sourceMethod, sourceClass, and parameter is logged.

     public  void entering(String sourceClass,
        String sourceMethod,
        Object[] params) 
      Log a method entry, with an array of parameters.

      This is a convenience method that can be used to log entry to a method. A LogRecord with message "ENTRY" (followed by a format {N} indicator for each entry in the parameter array), log level FINER, and the given sourceMethod, sourceClass, and parameters is logged.

     public  void exiting(String sourceClass,
        String sourceMethod) 
      Log a method return.

      This is a convenience method that can be used to log returning from a method. A LogRecord with message "RETURN", log level FINER, and the given sourceMethod and sourceClass is logged.

     public  void exiting(String sourceClass,
        String sourceMethod,
        Object result) 
      Log a method return, with result object.

      This is a convenience method that can be used to log returning from a method. A LogRecord with message "RETURN {0}", log level FINER, and the gives sourceMethod, sourceClass, and result object is logged.

     public  void fine(String msg) 
      Log a FINE message.

      If the logger is currently enabled for the FINE message level then the given message is forwarded to all the registered output Handler objects.

     public  void finer(String msg) 
      Log a FINER message.

      If the logger is currently enabled for the FINER message level then the given message is forwarded to all the registered output Handler objects.

     public  void finest(String msg) 
      Log a FINEST message.

      If the logger is currently enabled for the FINEST message level then the given message is forwarded to all the registered output Handler objects.

     public static Logger getAnonymousLogger() 
      Create an anonymous Logger. The newly created Logger is not registered in the LogManager namespace. There will be no access checks on updates to the logger.

      This factory method is primarily intended for use from applets. Because the resulting Logger is anonymous it can be kept private by the creating class. This removes the need for normal security checks, which in turn allows untrusted applet code to update the control state of the Logger. For example an applet can do a setLevel or an addHandler on an anonymous Logger.

      Even although the new logger is anonymous, it is configured to have the root logger ("") as its parent. This means that by default it inherits its effective level and handlers from the root logger.

     public static Logger getAnonymousLogger(String resourceBundleName) 
      Create an anonymous Logger. The newly created Logger is not registered in the LogManager namespace. There will be no access checks on updates to the logger.

      This factory method is primarily intended for use from applets. Because the resulting Logger is anonymous it can be kept private by the creating class. This removes the need for normal security checks, which in turn allows untrusted applet code to update the control state of the Logger. For example an applet can do a setLevel or an addHandler on an anonymous Logger.

      Even although the new logger is anonymous, it is configured to have the root logger ("") as its parent. This means that by default it inherits its effective level and handlers from the root logger.

     public Filter getFilter() 
      Get the current filter for this Logger.
     public static final Logger getGlobal() 
      Return global logger object with the name Logger.GLOBAL_LOGGER_NAME.
     public Handler[] getHandlers() 
      Get the Handlers associated with this logger.

     public Level getLevel() 
      Get the log Level that has been specified for this Logger. The result may be null, which means that this logger's effective level will be inherited from its parent.
     public static Logger getLogger(String name) 
      Find or create a logger for a named subsystem. If a logger has already been created with the given name it is returned. Otherwise a new logger is created.

      If a new logger is created its log level will be configured based on the LogManager configuration and it will configured to also send logging output to its parent's Handlers. It will be registered in the LogManager global namespace.

      Note: The LogManager may only retain a weak reference to the newly created Logger. It is important to understand that a previously created Logger with the given name may be garbage collected at any time if there is no strong reference to the Logger. In particular, this means that two back-to-back calls like {@code getLogger("MyLogger").log(...)} may use different Logger objects named "MyLogger" if there is no strong reference to the Logger named "MyLogger" elsewhere in the program.

     public static Logger getLogger(String name,
        String resourceBundleName) 
      Find or create a logger for a named subsystem. If a logger has already been created with the given name it is returned. Otherwise a new logger is created.

      If a new logger is created its log level will be configured based on the LogManager and it will configured to also send logging output to its parent's Handlers. It will be registered in the LogManager global namespace.

      Note: The LogManager may only retain a weak reference to the newly created Logger. It is important to understand that a previously created Logger with the given name may be garbage collected at any time if there is no strong reference to the Logger. In particular, this means that two back-to-back calls like {@code getLogger("MyLogger", ...).log(...)} may use different Logger objects named "MyLogger" if there is no strong reference to the Logger named "MyLogger" elsewhere in the program.

      If the named Logger already exists and does not yet have a localization resource bundle then the given resource bundle name is used. If the named Logger already exists and has a different resource bundle name then an IllegalArgumentException is thrown.

     public String getName() 
      Get the name for this logger.
     public Logger getParent() 
      Return the parent for this Logger.

      This method returns the nearest extant parent in the namespace. Thus if a Logger is called "a.b.c.d", and a Logger called "a.b" has been created but no logger "a.b.c" exists, then a call of getParent on the Logger "a.b.c.d" will return the Logger "a.b".

      The result will be null if it is called on the root Logger in the namespace.

     public ResourceBundle getResourceBundle() 
      Retrieve the localization resource bundle for this logger for the current default locale. Note that if the result is null, then the Logger will use a resource bundle inherited from its parent.
     public String getResourceBundleName() 
      Retrieve the localization resource bundle name for this logger. Note that if the result is null, then the Logger will use a resource bundle name inherited from its parent.
     public boolean getUseParentHandlers() 
      Discover whether or not this logger is sending its output to its parent logger.
     public  void info(String msg) 
      Log an INFO message.

      If the logger is currently enabled for the INFO message level then the given message is forwarded to all the registered output Handler objects.

     public boolean isLoggable(Level level) 
      Check if a message of the given level would actually be logged by this logger. This check is based on the Loggers effective level, which may be inherited from its parent.
     public  void log(LogRecord record) 
      Log a LogRecord.

      All the other logging methods in this class call through this method to actually perform any logging. Subclasses can override this single method to capture all log activity.

     public  void log(Level level,
        String msg) 
      Log a message, with no arguments.

      If the logger is currently enabled for the given message level then the given message is forwarded to all the registered output Handler objects.

     public  void log(Level level,
        String msg,
        Object param1) 
      Log a message, with one object parameter.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

     public  void log(Level level,
        String msg,
        Object[] params) 
      Log a message, with an array of object arguments.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

     public  void log(Level level,
        String msg,
        Throwable thrown) 
      Log a message, with associated Throwable information.

      If the logger is currently enabled for the given message level then the given arguments are stored in a LogRecord which is forwarded to all registered output handlers.

      Note that the thrown argument is stored in the LogRecord thrown property, rather than the LogRecord parameters property. Thus is it processed specially by output Formatters and is not treated as a formatting parameter to the LogRecord message property.

     public  void logp(Level level,
        String sourceClass,
        String sourceMethod,
        String msg) 
      Log a message, specifying source class and method, with no arguments.

      If the logger is currently enabled for the given message level then the given message is forwarded to all the registered output Handler objects.

     public  void logp(Level level,
        String sourceClass,
        String sourceMethod,
        String msg,
        Object param1) 
      Log a message, specifying source class and method, with a single object parameter to the log message.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

     public  void logp(Level level,
        String sourceClass,
        String sourceMethod,
        String msg,
        Object[] params) 
      Log a message, specifying source class and method, with an array of object arguments.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

     public  void logp(Level level,
        String sourceClass,
        String sourceMethod,
        String msg,
        Throwable thrown) 
      Log a message, specifying source class and method, with associated Throwable information.

      If the logger is currently enabled for the given message level then the given arguments are stored in a LogRecord which is forwarded to all registered output handlers.

      Note that the thrown argument is stored in the LogRecord thrown property, rather than the LogRecord parameters property. Thus is it processed specially by output Formatters and is not treated as a formatting parameter to the LogRecord message property.

     public  void logrb(Level level,
        String sourceClass,
        String sourceMethod,
        String bundleName,
        String msg) 
      Log a message, specifying source class, method, and resource bundle name with no arguments.

      If the logger is currently enabled for the given message level then the given message is forwarded to all the registered output Handler objects.

      The msg string is localized using the named resource bundle. If the resource bundle name is null, or an empty String or invalid then the msg string is not localized.

     public  void logrb(Level level,
        String sourceClass,
        String sourceMethod,
        String bundleName,
        String msg,
        Object param1) 
      Log a message, specifying source class, method, and resource bundle name, with a single object parameter to the log message.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

      The msg string is localized using the named resource bundle. If the resource bundle name is null, or an empty String or invalid then the msg string is not localized.

     public  void logrb(Level level,
        String sourceClass,
        String sourceMethod,
        String bundleName,
        String msg,
        Object[] params) 
      Log a message, specifying source class, method, and resource bundle name, with an array of object arguments.

      If the logger is currently enabled for the given message level then a corresponding LogRecord is created and forwarded to all the registered output Handler objects.

      The msg string is localized using the named resource bundle. If the resource bundle name is null, or an empty String or invalid then the msg string is not localized.

     public  void logrb(Level level,
        String sourceClass,
        String sourceMethod,
        String bundleName,
        String msg,
        Throwable thrown) 
      Log a message, specifying source class, method, and resource bundle name, with associated Throwable information.

      If the logger is currently enabled for the given message level then the given arguments are stored in a LogRecord which is forwarded to all registered output handlers.

      The msg string is localized using the named resource bundle. If the resource bundle name is null, or an empty String or invalid then the msg string is not localized.

      Note that the thrown argument is stored in the LogRecord thrown property, rather than the LogRecord parameters property. Thus is it processed specially by output Formatters and is not treated as a formatting parameter to the LogRecord message property.

     final  void removeChildLogger(LoggerWeakRef child) 
     public  void removeHandler(Handler handler) throws SecurityException 
      Remove a log Handler.

      Returns silently if the given Handler is not found or is null

     public  void setFilter(Filter newFilter) throws SecurityException 
      Set a filter to control output on this Logger.

      After passing the initial "level" check, the Logger will call this Filter to check if a log record should really be published.

     public  void setLevel(Level newLevel) throws SecurityException 
      Set the log level specifying which message levels will be logged by this logger. Message levels lower than this value will be discarded. The level value Level.OFF can be used to turn off logging.

      If the new level is null, it means that this node should inherit its level from its nearest ancestor with a specific (non-null) level value.

      void setLogManager(LogManager manager) 
     public  void setParent(Logger parent) 
      Set the parent for this Logger. This method is used by the LogManager to update a Logger when the namespace changes.

      It should not be called from application code.

     public  void setUseParentHandlers(boolean useParentHandlers) 
      Specify whether or not this logger should send its output to its parent Logger. This means that any LogRecords will also be written to the parent's Handlers, and potentially to its parent, recursively up the namespace.
     public  void severe(String msg) 
      Log a SEVERE message.

      If the logger is currently enabled for the SEVERE message level then the given message is forwarded to all the registered output Handler objects.

     public  void throwing(String sourceClass,
        String sourceMethod,
        Throwable thrown) 
      Log throwing an exception.

      This is a convenience method to log that a method is terminating by throwing an exception. The logging is done using the FINER level.

      If the logger is currently enabled for the given message level then the given arguments are stored in a LogRecord which is forwarded to all registered output handlers. The LogRecord's message is set to "THROW".

      Note that the thrown argument is stored in the LogRecord thrown property, rather than the LogRecord parameters property. Thus is it processed specially by output Formatters and is not treated as a formatting parameter to the LogRecord message property.

     public  void warning(String msg) 
      Log a WARNING message.

      If the logger is currently enabled for the WARNING message level then the given message is forwarded to all the registered output Handler objects.