Logger

Logger

java.util.logging

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Java 1.4

A Logger object is used to emit log messages. Logger does not have a public constructor, but there are several ways to obtain a Logger object to use in your code:

• Typically, applications call the static getLogger( ) method to create or lookup a named Logger within a hierarchy of named loggers. Loggers have dot-separated hierarchical names , which should be based on the name of the class or package that uses them. Loggers obtained in this way inherit their logging level, resource bundle (for localization), and Handler objects from their ancestors in the hierarchy and, ultimately, from the root Logger defined by the global LogManager .

• Applets that require a Logger with no security restrictions should use the static getAnonymousLogger( ) method to create an unnamed Logger that is not part of the hierarchy of named Logger objects managed by the LogManager . A Logger created by this method has the LogManager root logger as its parent, and inherits the logging level and handlers of that root logger.

• Finally, the static Logger.global field refers to a pre-defined Logger named "global"; programmers may find this pre-defined Logger convenient during the early stages of application development, but it should not be used in production code.

Once a suitable Logger has been obtained, there are a variety of methods that can be used to create a log message:

• The log( ) methods log a specified message at the specified level, with optional parameters that can be used in message localization. These methods examine the call stack and make an attempt to determine the class and method name from which the method is emitted . Because of code optimization and just-in-time compilation techniques, however, they may not always be able to determine this information.

• The logp( ) ("log precise") methods are like the log( ) methods but allow you to explicitly specify the name of the class and method that are emitting the log message.

• The logrb( ) methods are like the logp( ) methods, but additionally take the name of a resource bundle to use for localizing the message.

• entering( ) , exiting( ) , and tHRowing( ) are convenience methods for emitting log messages that trace the execution of a program. These methods use a logging level of Level.FINER . Note that there are variants of entering( ) and exiting( ) that allow specification of method arguments and return values.

• Finally, Logger defines a set of easy-to-use convenience methods for logging a simple message at a specific logging level. These methods have the same names as the logging levels: severe( ) , warning( ) , info ( ) , config( ) , fine( ) , finer( ) , finest( ) .

A Logger has an associated logging Level , and discards any log messages with a severity lower than this. The severity level is initialized from the system configuration file, which is usually the desired behavior. You can explicitly override this setting with setLevel( ) . You might want to do this if you created the Logger with getAnonymousLogger( ) and have read the desired logging level from a configuration file of your own. If level-based filtering of log messages is not sufficient, you can associate a Filter with your Logger by calling setFilter . If you do this, any log messages rejected by the Filter will be discarded.

A Logger sends its log messages to any Handler objects that have been registered with addHandler( ) . Call getHandlers( ) to obtain an array of all registered handlers, and call removeHandler( ) to de-register a handler. By default, all log messages are also sent to the handlers of the parent logger and any other ancestor loggers. Since all named and anonymous loggers have the LogManager root logger as a parent or ancestor, all loggers by default send their log messages to the handlers defined in the system logging configuration file. See LogManager for details. If you do not want a Logger to use the handlers of its ancestors, pass false to setUseParentHandlers( ) .

getLogger( ) and getAnonymousLogger( ) allow you to specify the name of a java.util.ResourceBundle for use in localizing log messages, and logrb( ) allows you to specify the name of a resource bundle to use to localize a specific log message. If a resource bundle is specified for the Logger or for a specific log message, then the message argument to the various logging methods is treated not as a literal message but instead as a localization key for which a localized version is to be looked up in the resource bundle. As part of the localization, any parameters, such as those specified by the param1 and params arguments to the log( ) method are substituted into the localized message string as per java.text.MessageFormat . (Note, however that this localization and formatting is not performed by the Logger itself: instead, it simply stores the ResourceBundle and parameters in the LogRecord . It is the Formatter associated with the output Handler object that actually performs the localization.)

All the methods of this class are threadsafe and do not require external synchronization.

 public class  Logger  {  // Protected Constructors  protected  Logger  (String  name  , String  resourceBundleName  );  // Public Constants  public static final Logger  global  ;  // Public Class Methods  public static Logger  getAnonymousLogger  ( );  synchronized  public static Logger  getAnonymousLogger  (String  resourceBundleName  );  synchronized  public static Logger  getLogger  (String  name  );  synchronized  public static Logger  getLogger  (String  name  , String  resourceBundleName  );  synchronized   // Public Instance Methods  public void  addHandler  (Handler  handler  ) throws SecurityException;  synchronized  public void  config  (String  msg  );        public void  entering  (String  sourceClass  , String  sourceMethod  );        public void  entering  (String  sourceClass  , String  sourceMethod  , Object  param1  );        public void  entering  (String  sourceClass  , String  sourceMethod  , Object[ ]  params  );        public void  exiting  (String  sourceClass  , String  sourceMethod  );        public void  exiting  (String  sourceClass  , String  sourceMethod  , Object  result  );        public void  fine  (String  msg  );        public void  finer  (String  msg  );        public void  finest  (String  msg  );        public Filter  getFilter  ( );        public Handler[ ]  getHandlers  ( );  synchronized  public Level  getLevel  ( );        public String  getName  ( );        public Logger  getParent  ( );        public java.util.ResourceBundle  getResourceBundle  ( );        public String  getResourceBundleName  ( );        public boolean  getUseParentHandlers  ( );  synchronized  public void  info  (String  msg  );        public boolean  isLoggable  (Level  level  );        public void  log  (LogRecord  record  );        public void  log  (Level  level  , String  msg  );        public void  log  (Level  level  , String  msg  , Throwable  thrown  );        public void  log  (Level  level  , String  msg  , Object  param1  );        public void  log  (Level  level  , String  msg  , Object[ ]  params  );        public void  logp  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  msg  );        public void  logp  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  msg  , Object  param1  );        public void  logp  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  msg  , Object[ ]  params  );        public void  logp  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  msg  , Throwable  thrown  );        public void  logrb  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  bundleName  , String  msg  );        public void  logrb  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  bundleName  , String  msg  , Object  param1  );        public void logrb(Level  level  , String  sourceClass  , String  sourceMethod  ,          String  bundleName  , String  msg  , Throwable  thrown  );        public void  logrb  (Level  level  , String  sourceClass  , String  sourceMethod  ,          String  bundleName  , String  msg  , Object[ ]  params  );        public void  removeHandler  (Handler  handler  ) throws SecurityException;  synchronized  public void  setFilter  (Filter  newFilter  ) throws SecurityException;        public void  setLevel  (Level  newLevel  ) throws SecurityException;        public void  setParent  (Logger  parent  );        public void  setUseParentHandlers  (boolean  useParentHandlers  );  synchronized  public void  severe  (String  msg  );        public void  throwing  (String  sourceClass  , String  sourceMethod  , Throwable  thrown  );        public void  warning  (String  msg  );   } 

Passed To

LogManager.addLogger( )

Returned By

LogManager.getLogger( )