Logger JDK 1.6)

Description

public class Logger

A Logger object is used to log messages for a specific system or application component.

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.

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:

There are a set of "log" methods that take a log level, a message string, and optionally some parameters to the message string.
There are a set of "logp" methods (for "log precise") that are like the "log" methods, but also take an explicit source class name and method name.
There are a set of "logrb" method (for "log with resource bundle") that are like the "logp" method, but also take an explicit resource bundle name for use in localizing the log message.
There are convenience methods for tracing method entries (the "entering" methods), method returns (the "exiting" methods) and throwing exceptions (the "throwing" methods).
Finally, there are a set of convenience methods for use in the very simplest cases, when a developer simply wants to log a simple string at a given log level. These methods are named after the standard Level names ("severe", "warning", "info", etc.) and take a single argument, a message string.

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.

See also:

Methods

Hide/Show inherited methods

publicsynchronized void addHandler (Handler handler) throws SecurityException

Add a log Handler to receive logging messages.

public void config (String msg)

Log a CONFIG message.

public void entering (String sourceClass, String sourceMethod)

Log a method entry.

public void entering (String sourceClass, String sourceMethod, Object param1)

Log a method entry, with one parameter.

public void entering (String sourceClass, String sourceMethod, Object params)

Log a method entry, with an array of parameters.

public void exiting (String sourceClass, String sourceMethod)

Log a method return.

public void exiting (String sourceClass, String sourceMethod, Object result)

Log a method return, with result object.

public void fine (String msg)

Log a FINE message.

public void finer (String msg)

Log a FINER message.

public void finest (String msg)

Log a FINEST message.

publicstaticsynchronized Logger getAnonymousLogger ()

Create an anonymous Logger.

publicstaticsynchronized Logger getAnonymousLogger (String resourceBundleName)

Create an anonymous Logger.

public Filter getFilter ()

Get the current filter for this Logger.

publicsynchronized Handler getHandlers ()

Get the Handlers associated with this logger.

public Level getLevel ()

Get the log Level that has been specified for this Logger.

publicstaticsynchronized Logger getLogger (String name)

Find or create a logger for a named subsystem.

publicstaticsynchronized Logger getLogger (String name, String resourceBundleName)

Find or create a logger for a named subsystem.

public String getName ()

Get the name for this logger.

public Logger getParent ()

Return the parent for this Logger.

public ResourceBundle getResourceBundle ()

Retrieve the localization resource bundle for this logger for the current default locale.

public String getResourceBundleName ()

Retrieve the localization resource bundle name for this logger.

publicsynchronized 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.

public boolean isLoggable (Level level)

Check if a message of the given level would actually be logged by this logger.

public void log (Level level, String msg)

Log a message, with no arguments.

public void log (Level level, String msg, Object param1)

Log a message, with one object parameter.

public void log (Level level, String msg, Object params)

Log a message, with an array of object arguments.

public void log (Level level, String msg, Throwable thrown)

Log a message, with associated Throwable information.

public void log (LogRecord record)

Log a LogRecord.

public void logp (Level level, String sourceClass, String sourceMethod, String msg)

Log a message, specifying source class and method, with no arguments.

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.

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.

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.

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.

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.

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.

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.

publicsynchronized void removeHandler (Handler handler) throws SecurityException

Remove a log Handler.

public void setFilter (Filter newFilter) throws SecurityException

Set a filter to control output on this Logger.

public void setLevel (Level newLevel) throws SecurityException

Set the log level specifying which message levels will be logged by this logger.

pack-private void setLogManager (LogManager manager)

public void setParent (Logger parent)

Set the parent for this Logger.

publicsynchronized void setUseParentHandlers (boolean useParentHandlers)

Specify whether or not this logger should send its output to it's parent Logger.

public void severe (String msg)

Log a SEVERE message.

public void throwing (String sourceClass, String sourceMethod, Throwable thrown)

Log throwing an exception.

public void warning (String msg)

Log a WARNING message.