public class Logger extends Object
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 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:
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.
| Modifier and Type | Field and Description |
|---|---|
static Logger |
global
Deprecated.
Initialization of this field is prone to deadlocks.
The field must be initialized by the Logger class initialization
which may cause deadlocks with the LogManager class initialization.
In such cases two class initialization wait for each other to complete.
The preferred way to get the global logger object is via the call
Logger.getGlobal().
For compatibility with old JDK versions where the
Logger.getGlobal() is not available use the call
Logger.getLogger(Logger.GLOBAL_LOGGER_NAME)
or Logger.getLogger("global"). |
static String |
GLOBAL_LOGGER_NAME
GLOBAL_LOGGER_NAME is a name for the global logger.
|
| Modifier | Constructor and Description |
|---|---|
protected |
Logger(String name,
String resourceBundleName)
Protected method to construct a logger for a named subsystem.
|
| Modifier and Type | Method and Description |
|---|---|
void |
addHandler(Handler handler)
Add a log Handler to receive logging messages.
|
void |
config(String msg)
Log a CONFIG message.
|
void |
entering(String sourceClass,
String sourceMethod)
Log a method entry.
|
void |
entering(String sourceClass,
String sourceMethod,
Object param1)
Log a method entry, with one parameter.
|
void |
entering(String sourceClass,
String sourceMethod,
Object[] params)
Log a method entry, with an array of parameters.
|
void |
exiting(String sourceClass,
String sourceMethod)
Log a method return.
|
void |
exiting(String sourceClass,
String sourceMethod,
Object result)
Log a method return, with result object.
|
void |
fine(String msg)
Log a FINE message.
|
void |
finer(String msg)
Log a FINER message.
|
void |
finest(String msg)
Log a FINEST message.
|
static Logger |
getAnonymousLogger()
Create an anonymous Logger.
|
static Logger |
getAnonymousLogger(String resourceBundleName)
Create an anonymous Logger.
|
Filter |
getFilter()
Get the current filter for this Logger.
|
static Logger |
getGlobal()
Return global logger object with the name Logger.GLOBAL_LOGGER_NAME.
|
Handler[] |
getHandlers()
Get the Handlers associated with this logger.
|
Level |
getLevel()
Get the log Level that has been specified for this Logger.
|
static Logger |
getLogger(String name)
Find or create a logger for a named subsystem.
|
static Logger |
getLogger(String name,
String resourceBundleName)
Find or create a logger for a named subsystem.
|
String |
getName()
Get the name for this logger.
|
Logger |
getParent()
Return the parent for this Logger.
|
ResourceBundle |
getResourceBundle()
Retrieve the localization resource bundle for this
logger for the current default locale.
|
String |
getResourceBundleName()
Retrieve the localization resource bundle name for this
logger.
|
boolean |
getUseParentHandlers()
Discover whether or not this logger is sending its output
to its parent logger.
|
void |
info(String msg)
Log an INFO message.
|
boolean |
isLoggable(Level level)
Check if a message of the given level would actually be logged
by this logger.
|
void |
log(Level level,
String msg)
Log a message, with no arguments.
|
void |
log(Level level,
String msg,
Object param1)
Log a message, with one object parameter.
|
void |
log(Level level,
String msg,
Object[] params)
Log a message, with an array of object arguments.
|
void |
log(Level level,
String msg,
Throwable thrown)
Log a message, with associated Throwable information.
|
void |
log(LogRecord record)
Log a LogRecord.
|
void |
logp(Level level,
String sourceClass,
String sourceMethod,
String msg)
Log a message, specifying source class and method,
with no arguments.
|
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.
|
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.
|
void |
logp(Level level,
String sourceClass,
String sourceMethod,
String msg,
Throwable thrown)
Log a message, specifying source class and method,
with associated Throwable information.
|
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.
|
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.
|
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.
|
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.
|
void |
removeHandler(Handler handler)
Remove a log Handler.
|
void |
setFilter(Filter newFilter)
Set a filter to control output on this Logger.
|
void |
setLevel(Level newLevel)
Set the log level specifying which message levels will be
logged by this logger.
|
void |
setParent(Logger parent)
Set the parent for this Logger.
|
void |
setUseParentHandlers(boolean useParentHandlers)
Specify whether or not this logger should send its output
to its parent Logger.
|
void |
severe(String msg)
Log a SEVERE message.
|
void |
throwing(String sourceClass,
String sourceMethod,
Throwable thrown)
Log throwing an exception.
|
void |
warning(String msg)
Log a WARNING message.
|
public static final String GLOBAL_LOGGER_NAME
@Deprecated public static final Logger global
Logger.getGlobal().
For compatibility with old JDK versions where the
Logger.getGlobal() is not available use the call
Logger.getLogger(Logger.GLOBAL_LOGGER_NAME)
or Logger.getLogger("global").protected Logger(String name, String resourceBundleName)
The logger will be initially configured with a null Level and with useParentHandlers set to true.
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.MissingResourceException - if the resourceBundleName is non-null and
no corresponding resource can be found.public static final Logger getGlobal()
public static Logger getLogger(String name)
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
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.
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.swingNullPointerException - if the name is null.public static Logger getLogger(String name, String resourceBundleName)
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
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.
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.swingresourceBundleName - name of ResourceBundle to be used for localizing
messages for this logger. May be null if none of
the messages require localization.MissingResourceException - if the resourceBundleName is non-null and
no corresponding resource can be found.IllegalArgumentException - if the Logger already exists and uses
a different resource bundle name.NullPointerException - if the name is null.public static Logger getAnonymousLogger()
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)
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.
resourceBundleName - name of ResourceBundle to be used for localizing
messages for this logger.
May be null if none of the messages require localization.MissingResourceException - if the resourceBundleName is non-null and
no corresponding resource can be found.public ResourceBundle getResourceBundle()
public String getResourceBundleName()
public void setFilter(Filter newFilter) throws SecurityException
After passing the initial "level" check, the Logger will call this Filter to check if a log record should really be published.
newFilter - a filter object (may be null)SecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control").public Filter getFilter()
public void log(LogRecord record)
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.
record - the LogRecord to be publishedpublic void log(Level level, String msg)
If the logger is currently enabled for the given message level then the given message is forwarded to all the registered output Handler objects.
level - One of the message level identifiers, e.g., SEVEREmsg - The string message (or a key in the message catalog)public void log(Level level, String msg, Object param1)
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.
level - One of the message level identifiers, e.g., SEVEREmsg - The string message (or a key in the message catalog)param1 - parameter to the messagepublic void log(Level level, String msg, Object[] params)
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.
level - One of the message level identifiers, e.g., SEVEREmsg - The string message (or a key in the message catalog)params - array of parameters to the messagepublic void log(Level level, String msg, Throwable thrown)
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.
level - One of the message level identifiers, e.g., SEVEREmsg - The string message (or a key in the message catalog)thrown - Throwable associated with log message.public void logp(Level level, String sourceClass, String sourceMethod, String msg)
If the logger is currently enabled for the given message level then the given message is forwarded to all the registered output Handler objects.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestmsg - The string message (or a key in the message catalog)public void logp(Level level, String sourceClass, String sourceMethod, String msg, Object param1)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestmsg - The string message (or a key in the message catalog)param1 - Parameter to the log message.public void logp(Level level, String sourceClass, String sourceMethod, String msg, Object[] params)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestmsg - The string message (or a key in the message catalog)params - Array of parameters to the messagepublic void logp(Level level, String sourceClass, String sourceMethod, String msg, Throwable thrown)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestmsg - The string message (or a key in the message catalog)thrown - Throwable associated with log message.public void logrb(Level level, String sourceClass, String sourceMethod, String bundleName, String msg)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestbundleName - name of resource bundle to localize msg,
can be nullmsg - The string message (or a key in the message catalog)public void logrb(Level level, String sourceClass, String sourceMethod, String bundleName, String msg, Object param1)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestbundleName - name of resource bundle to localize msg,
can be nullmsg - The string message (or a key in the message catalog)param1 - Parameter to the log message.public void logrb(Level level, String sourceClass, String sourceMethod, String bundleName, String msg, Object[] params)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestbundleName - name of resource bundle to localize msg,
can be null.msg - The string message (or a key in the message catalog)params - Array of parameters to the messagepublic void logrb(Level level, String sourceClass, String sourceMethod, String bundleName, String msg, Throwable thrown)
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.
level - One of the message level identifiers, e.g., SEVEREsourceClass - name of class that issued the logging requestsourceMethod - name of method that issued the logging requestbundleName - name of resource bundle to localize msg,
can be nullmsg - The string message (or a key in the message catalog)thrown - Throwable associated with log message.public void entering(String sourceClass, String sourceMethod)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of method that is being enteredpublic void entering(String sourceClass, String sourceMethod, Object param1)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of method that is being enteredparam1 - parameter to the method being enteredpublic void entering(String sourceClass, String sourceMethod, Object[] params)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of method that is being enteredparams - array of parameters to the method being enteredpublic void exiting(String sourceClass, String sourceMethod)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of the methodpublic void exiting(String sourceClass, String sourceMethod, Object result)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of the methodresult - Object that is being returnedpublic void throwing(String sourceClass, String sourceMethod, Throwable thrown)
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.
sourceClass - name of class that issued the logging requestsourceMethod - name of the method.thrown - The Throwable that is being thrown.public void severe(String msg)
If the logger is currently enabled for the SEVERE message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void warning(String msg)
If the logger is currently enabled for the WARNING message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void info(String msg)
If the logger is currently enabled for the INFO message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void config(String msg)
If the logger is currently enabled for the CONFIG message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void fine(String msg)
If the logger is currently enabled for the FINE message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void finer(String msg)
If the logger is currently enabled for the FINER message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void finest(String msg)
If the logger is currently enabled for the FINEST message level then the given message is forwarded to all the registered output Handler objects.
msg - The string message (or a key in the message catalog)public void setLevel(Level newLevel) throws SecurityException
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.
newLevel - the new value for the log level (may be null)SecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control").public Level getLevel()
public boolean isLoggable(Level level)
level - a message logging levelpublic String getName()
public void addHandler(Handler handler) throws SecurityException
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.
handler - a logging HandlerSecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control").public void removeHandler(Handler handler) throws SecurityException
Returns silently if the given Handler is not found or is null
handler - a logging HandlerSecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control").public Handler[] getHandlers()
public void setUseParentHandlers(boolean useParentHandlers)
useParentHandlers - true if output is to be sent to the
logger's parent.SecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control").public boolean getUseParentHandlers()
public Logger getParent()
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 void setParent(Logger parent)
It should not be called from application code.
parent - the new parent loggerSecurityException - if a security manager exists and if
the caller does not have LoggingPermission("control"). Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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