Class System.LoggerFinder
- Enclosing class:
System
LoggerFinder service is responsible for creating, managing,
and configuring loggers to the underlying framework it uses.
A logger finder is a concrete implementation of this class that has a
zero-argument constructor and implements the abstract methods defined
by this class.
The loggers returned from a logger finder are capable of routing log
messages to the logging backend this provider supports.
A given invocation of the Java Runtime maintains a single
system-wide LoggerFinder instance that is loaded as follows:
- First it finds any custom
LoggerFinderprovider using theServiceLoaderfacility with the system class loader. - If no
LoggerFinderprovider is found, the system defaultLoggerFinderimplementation will be used.
An application can replace the logging backend
even when the java.logging module is present, by simply providing
and declaring an implementation of the System.LoggerFinder service.
Default Implementation
The system default LoggerFinder implementation uses
java.util.logging as the backend framework when the
java.logging module is present.
It returns a logger instance
that will route log messages to a java.util.logging.Logger. Otherwise, if java.logging is not
present, the default implementation will return a simple logger
instance that will route log messages of INFO level and above to
the console (System.err).
Logging Configuration
Logger instances obtained from the
LoggerFinder factory methods are not directly configurable by
the application. Configuration is the responsibility of the underlying
logging backend, and usually requires using APIs specific to that backend.
For the default LoggerFinder implementation
using java.util.logging as its backend, refer to
java.util.logging for logging configuration.
For the default LoggerFinder implementation returning simple loggers
when the java.logging module is absent, the configuration
is implementation dependent.
Usually an application that uses a logging framework will log messages through a logger facade defined (or supported) by that framework. Applications that wish to use an external framework should log through the facade associated with that framework.
A system class that needs to log messages will typically obtain
a System.Logger instance to route messages to the logging
framework selected by the application.
Libraries and classes that only need loggers to produce log messages
should not attempt to configure loggers by themselves, as that
would make them dependent from a specific implementation of the
LoggerFinder service.
Message Levels and Mapping to backend levels
A logger finder is responsible for mapping from a
System.Logger.Level to a level supported by the logging backend it uses.
The default LoggerFinder using java.util.logging as the backend
maps System.Logger levels to
java.util.logging levels
of corresponding severity - as described in Logger.Level.
- Since:
- 9
- See Also:
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptiongetLocalizedLogger(String name, ResourceBundle bundle, Module module) Returns a localizable instance ofLoggerfor the givenmodule.abstract System.LoggerReturns an instance ofLoggerfor the givenmodule.static System.LoggerFinderReturns theLoggerFinderinstance.
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Constructor Details
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LoggerFinder
protected LoggerFinder()Creates a new instance ofLoggerFinder.- Implementation Note:
- It is recommended that a
LoggerFinderservice implementation does not perform any heavy initialization in its constructor, in order to avoid possible risks of deadlock or class loading cycles during the instantiation of the service provider.
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Method Details
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getLogger
Returns an instance ofLoggerfor the givenmodule.- Parameters:
name- the name of the logger.module- the module for which the logger is being requested.- Returns:
- a
loggersuitable for use within the given module. - Throws:
NullPointerException- ifnameisnullormoduleisnull.
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getLocalizedLogger
Returns a localizable instance ofLoggerfor the givenmodule. The returned logger will use the provided resource bundle for message localization.- Implementation Requirements:
- By default, this method calls
this.getLogger(name, module)to obtain a logger, then wraps that logger in aSystem.Loggerinstance where all methods that do not take aResourceBundleas parameter are redirected to one which does - passing the givenbundlefor localization. So for instance, a call toLogger.log(Level.INFO, msg)will end up as a call toLogger.log(Level.INFO, bundle, msg, (Object[])null)on the wrapped logger instance. Note however that by default, string messages returned bySupplier<String>will not be localized, as it is assumed that such strings are messages which are already constructed, rather than keys in a resource bundle.An implementation of
LoggerFindermay override this method, for example, when the underlying logging backend provides its own mechanism for localizing log messages, then such aLoggerFinderwould be free to return a logger that makes direct use of the mechanism provided by the backend. - Parameters:
name- the name of the logger.bundle- a resource bundle; can benull.module- the module for which the logger is being requested.- Returns:
- an instance of
Loggerwhich will use the provided resource bundle for message localization. - Throws:
NullPointerException- ifnameisnullormoduleisnull.
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getLoggerFinder
Returns theLoggerFinderinstance. There is one single system-wideLoggerFinderinstance in the Java Runtime. See the class specification of how theLoggerFinderimplementation is located and loaded.- Returns:
- the
LoggerFinderinstance.
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