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FileHandler

public class FileHandler
extends StreamHandler

java.lang.Object
   ↳ java.util.logging.Handler
     ↳ java.util.logging.StreamHandler
       ↳ java.util.logging.FileHandler


Simple file logging Handler.

The FileHandler can either write to a specified file, or it can write to a rotating set of files.

For a rotating set of files, as each file reaches a given size limit, it is closed, rotated out, and a new file opened. Successively older files are named by adding "0", "1", "2", etc. into the base filename.

By default buffering is enabled in the IO libraries but each log record is flushed out when it is complete.

By default the XMLFormatter class is used for formatting.

Configuration: By default each FileHandler is initialized using the following LogManager configuration properties. If properties are not defined (or have invalid values) then the specified default values are used.

  • java.util.logging.FileHandler.level specifies the default level for the Handler (defaults to Level.ALL).
  • java.util.logging.FileHandler.filter specifies the name of a Filter class to use (defaults to no Filter).
  • java.util.logging.FileHandler.formatter specifies the name of a Formatter class to use (defaults to java.util.logging.XMLFormatter)
  • java.util.logging.FileHandler.encoding the name of the character set encoding to use (defaults to the default platform encoding).
  • java.util.logging.FileHandler.limit specifies an approximate maximum amount to write (in bytes) to any one file. If this is zero, then there is no limit. (Defaults to no limit).
  • java.util.logging.FileHandler.count specifies how many output files to cycle through (defaults to 1).
  • java.util.logging.FileHandler.pattern specifies a pattern for generating the output file name. See below for details. (Defaults to "%h/java%u.log").
  • java.util.logging.FileHandler.append specifies whether the FileHandler should append onto any existing files (defaults to false).

A pattern consists of a string that includes the following special components that will be replaced at runtime:

  • "/" the local pathname separator
  • "%t" the system temporary directory
  • "%h" the value of the "user.home" system property
  • "%g" the generation number to distinguish rotated logs
  • "%u" a unique number to resolve conflicts
  • "%%" translates to a single percent sign "%"
If no "%g" field has been specified and the file count is greater than one, then the generation number will be added to the end of the generated filename, after a dot.

Thus for example a pattern of "%t/java%g.log" with a count of 2 would typically cause log files to be written on Solaris to /var/tmp/java0.log and /var/tmp/java1.log whereas on Windows 95 they would be typically written to C:\TEMP\java0.log and C:\TEMP\java1.log

Generation numbers follow the sequence 0, 1, 2, etc.

Normally the "%u" unique field is set to 0. However, if the FileHandler tries to open the filename and finds the file is currently in use by another process it will increment the unique number field and try again. This will be repeated until FileHandler finds a file name that is not currently in use. If there is a conflict and no "%u" field has been specified, it will be added at the end of the filename after a dot. (This will be after any automatically added generation number.)

Thus if three processes were all trying to log to fred%u.%g.txt then they might end up using fred0.0.txt, fred1.0.txt, fred2.0.txt as the first file in their rotating sequences.

Note that the use of unique ids to avoid conflicts is only guaranteed to work reliably when using a local disk file system.

Summary

Public constructors

FileHandler()

Construct a default FileHandler.

FileHandler(String pattern)

Initialize a FileHandler to write to the given filename.

FileHandler(String pattern, boolean append)

Initialize a FileHandler to write to the given filename, with optional append.

FileHandler(String pattern, int limit, int count)

Initialize a FileHandler to write to a set of files.

FileHandler(String pattern, int limit, int count, boolean append)

Initialize a FileHandler to write to a set of files with optional append.

Public methods

void close()

Close all the files.

void publish(LogRecord record)

Format and publish a LogRecord.

Inherited methods

From class java.util.logging.StreamHandler
From class java.util.logging.Handler
From class java.lang.Object

Public constructors

FileHandler

Added in API level 1
FileHandler ()

Construct a default FileHandler. This will be configured entirely from LogManager properties (or their default values).

Throws
IOException if there are IO problems opening the files.
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control")).
NullPointerException if pattern property is an empty String.

FileHandler

Added in API level 1
FileHandler (String pattern)

Initialize a FileHandler to write to the given filename.

The FileHandler is configured based on LogManager properties (or their default values) except that the given pattern argument is used as the filename pattern, the file limit is set to no limit, and the file count is set to one.

There is no limit on the amount of data that may be written, so use this with care.

Parameters
pattern String: the name of the output file
Throws
IOException if there are IO problems opening the files.
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control").
IllegalArgumentException if pattern is an empty string

FileHandler

Added in API level 1
FileHandler (String pattern, 
                boolean append)

Initialize a FileHandler to write to the given filename, with optional append.

The FileHandler is configured based on LogManager properties (or their default values) except that the given pattern argument is used as the filename pattern, the file limit is set to no limit, the file count is set to one, and the append mode is set to the given append argument.

There is no limit on the amount of data that may be written, so use this with care.

Parameters
pattern String: the name of the output file
append boolean: specifies append mode
Throws
IOException if there are IO problems opening the files.
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control").
IllegalArgumentException if pattern is an empty string

FileHandler

Added in API level 1
FileHandler (String pattern, 
                int limit, 
                int count)

Initialize a FileHandler to write to a set of files. When (approximately) the given limit has been written to one file, another file will be opened. The output will cycle through a set of count files.

The FileHandler is configured based on LogManager properties (or their default values) except that the given pattern argument is used as the filename pattern, the file limit is set to the limit argument, and the file count is set to the given count argument.

The count must be at least 1.

Parameters
pattern String: the pattern for naming the output file
limit int: the maximum number of bytes to write to any one file
count int: the number of files to use
Throws
IOException if there are IO problems opening the files.
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control").
IllegalArgumentException if limit < 0, or count < 1.
IllegalArgumentException if pattern is an empty string

FileHandler

Added in API level 1
FileHandler (String pattern, 
                int limit, 
                int count, 
                boolean append)

Initialize a FileHandler to write to a set of files with optional append. When (approximately) the given limit has been written to one file, another file will be opened. The output will cycle through a set of count files.

The FileHandler is configured based on LogManager properties (or their default values) except that the given pattern argument is used as the filename pattern, the file limit is set to the limit argument, and the file count is set to the given count argument, and the append mode is set to the given append argument.

The count must be at least 1.

Parameters
pattern String: the pattern for naming the output file
limit int: the maximum number of bytes to write to any one file
count int: the number of files to use
append boolean: specifies append mode
Throws
IOException if there are IO problems opening the files.
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control").
IllegalArgumentException if limit < 0, or count < 1.
IllegalArgumentException if pattern is an empty string

Public methods

close

Added in API level 1
void close ()

Close all the files.

Throws
SecurityException if a security manager exists and if the caller does not have LoggingPermission("control").

publish

Added in API level 1
void publish (LogRecord record)

Format and publish a LogRecord.

Parameters
record LogRecord: description of the log event. A null record is silently ignored and is not published
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