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Class FileHandler

java.lang.Object
java.util.logging.Handler
java.util.logging.StreamHandler
java.util.logging.FileHandler
public class FileHandler extends StreamHandler
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 where <handler-name> refers to the fully-qualified class name of the handler. If properties are not defined (or have invalid values) then the specified default values are used.

  • <handler-name>.level specifies the default level for the Handler (defaults to Level.ALL).
  • <handler-name>.filter specifies the name of a Filter class to use (defaults to no Filter).
  • <handler-name>.formatter specifies the name of a Formatter class to use (defaults to java.util.logging.XMLFormatter)
  • <handler-name>.encoding the name of the character set encoding to use (defaults to the default platform encoding).
  • <handler-name>.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).
  • <handler-name>.count specifies how many output files to cycle through (defaults to 1).
  • <handler-name>.pattern specifies a pattern for generating the output file name. See below for details. (Defaults to "%h/java%u.log").
  • <handler-name>.append specifies whether the FileHandler should append onto any existing files (defaults to false).
  • <handler-name>.maxLocks specifies the maximum number of concurrent locks held by FileHandler (defaults to 100).

For example, the properties for FileHandler would be:

  • java.util.logging.FileHandler.level=INFO
  • java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter

For a custom handler, e.g. com.foo.MyHandler, the properties would be:

  • com.foo.MyHandler.level=INFO
  • com.foo.MyHandler.formatter=java.util.logging.SimpleFormatter

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.

Since:
1.4

Constructor Summary

Constructor Description
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.
FileHandler(String pattern, long limit, int count, boolean append)
Initialize a FileHandler to write to a set of files with optional append.

Method Summary

Modifier and Type Method Description
void close()
Close all the files.
void publish(LogRecord record)
Format and publish a LogRecord.

Methods declared in class java.util.logging.StreamHandler

flush, isLoggable, setEncoding, setOutputStream

Methods declared in class java.util.logging.Handler

getEncoding, getErrorManager, getFilter, getFormatter, getLevel, reportError, setErrorManager, setFilter, setFormatter, setLevel

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

FileHandler

public FileHandler() throws IOException, SecurityException
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

public FileHandler(String pattern) throws IOException, SecurityException
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 - 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

public FileHandler(String pattern, boolean append) throws IOException, SecurityException
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 - the name of the output file
append - 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

public FileHandler(String pattern, int limit, int count) throws IOException, SecurityException
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 - the pattern for naming the output file
limit - the maximum number of bytes to write to any one file
count - 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

public FileHandler(String pattern, int limit, int count, boolean append) throws IOException, SecurityException
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 - the pattern for naming the output file
limit - the maximum number of bytes to write to any one file
count - the number of files to use
append - 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

FileHandler

public FileHandler(String pattern, long limit, int count, boolean append) throws IOException
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 - the pattern for naming the output file
limit - the maximum number of bytes to write to any one file
count - the number of files to use
append - 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
Since:
9

Method Details

publish

public void publish(LogRecord record)
Format and publish a LogRecord.
Overrides:
publish in class StreamHandler
Parameters:
record - description of the log event. A null record is silently ignored and is not published

close

public void close() throws SecurityException
Close all the files.
Overrides:
close in class StreamHandler
Throws:
SecurityException - if a security manager exists and if the caller does not have LoggingPermission("control").

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.logging/java/util/logging/FileHandler.html