OpenJDK 27 · java.util.logging.MemoryHandler · APIdia, the JavaDoc alternative

Handler that buffers requests in a circular buffer in memory.

Normally this Handler simply stores incoming LogRecords into its memory buffer and discards earlier records. This buffering is very cheap and avoids formatting costs. On certain trigger conditions, the MemoryHandler will push out its current buffer contents to a target Handler, which will typically publish them to the outside world.

There are three main models for triggering a push of the buffer:

An incoming LogRecord has a type that is greater than a pre-defined level, the pushLevel.
An external class calls the push method explicitly.
A subclass overrides the log method and scans each incoming LogRecord and calls push if a record matches some desired criteria.

Configuration: By default each MemoryHandler 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. If no default value is defined then a RuntimeException is thrown.

<handler-name>.level specifies the 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>.size defines the buffer size (defaults to 1000).
<handler-name>.push defines the pushLevel (defaults to level.SEVERE).
<handler-name>.target specifies the name of the target Handler class. (no default).

For example, the properties for MemoryHandler would be:

java.util.logging.MemoryHandler.level=INFO
java.util.logging.MemoryHandler.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

Field Summary

Modifier and Type	Field and Description
private LogRecord[]	buffer
pack-priv int	count
private static final int	DEFAULT_SIZE
private volatile Level	pushLevel
private int	size
pack-priv int	start
private Handler	target

Constructor Summary

Access	Constructor and Description
public	MemoryHandler() Create a `MemoryHandler` and configure it based on `LogManager` configuration properties.
public	MemoryHandler(Handler the Handler to which to publish output. target, int the number of log records to buffer (must be greater than zero) size, Level message level to push on pushLevel) Create a `MemoryHandler`.

Method Summary

Modifier and Type	Method and Description
public void	close() Implements abstract java.util.logging.Handler.close. Close the `Handler` and free all associated resources.
public void	flush() Implements abstract java.util.logging.Handler.flush. Causes a flush on the target `Handler`.
public Level	Returns: the value of the `pushLevel` getPushLevel() Get the `pushLevel`.
private void	init()
public boolean	Returns: true if the `LogRecord` would be logged. isLoggable(LogRecord a `LogRecord` (may be null). record) Overrides java.util.logging.Handler.isLoggable. Check if this `Handler` would actually log a given `LogRecord` into its internal buffer.
public synchronized void	publish(LogRecord description of the log event. A null record is silently ignored and is not published record) Implements abstract java.util.logging.Handler.publish. Store a `LogRecord` in an internal buffer.
public synchronized void	push() Push any buffered output to the target `Handler`.
public synchronized void	setPushLevel(Level the new value of the `pushLevel` newLevel) Set the `pushLevel`.

Inherited from java.util.logging.Handler:: getEncoding getErrorManager getFilter getFormatter getLevel reportError setEncoding setErrorManager setFilter setFormatter setLevel

Field Detail

buffer	back to summary
private LogRecord[] buffer

count	back to summary
pack-priv int count

DEFAULT_SIZE	back to summary
private static final int DEFAULT_SIZE

pushLevel	back to summary
private volatile Level pushLevel

size	back to summary
private int size

start	back to summary
pack-priv int start

target	back to summary
private Handler target

Constructor Detail

MemoryHandler	back to summary
public MemoryHandler() Create a `MemoryHandler` and configure it based on `LogManager` configuration properties.

MemoryHandler back to summary

MemoryHandler	back to summary
public MemoryHandler(Handler target, int size, Level pushLevel) Create a `MemoryHandler`. The `MemoryHandler` is configured based on `LogManager` properties (or their default values) except that the given `pushLevel` argument and buffer size argument are used. Parameters target:Handler the Handler to which to publish output. size:int the number of log records to buffer (must be greater than zero) pushLevel:Level message level to push on Exceptions IllegalArgumentException: if `size is <= 0`

public MemoryHandler(Handler target, int size, Level pushLevel)

Create a MemoryHandler.

The MemoryHandler is configured based on LogManager properties (or their default values) except that the given pushLevel argument and buffer size argument are used.

Parameters

target:Handler: the Handler to which to publish output.
size:int: the number of log records to buffer (must be greater than zero)
pushLevel:Level: message level to push on

Exceptions

IllegalArgumentException:: if size is <= 0

Method Detail

close back to summary

close	back to summary
public void close() Implements abstract java.util.logging.Handler.close. Close the `Handler` and free all associated resources. This will also close the target `Handler`. Annotations @Override

public void close()

Implements abstract java.util.logging.Handler.close.

Close the Handler and free all associated resources. This will also close the target Handler.

Annotations

@Override

flush back to summary

flush	back to summary
public void flush() Implements abstract java.util.logging.Handler.flush. Causes a flush on the target `Handler`. Note that the current contents of the `MemoryHandler` buffer are not written out. That requires a "push". Annotations @Override

public void flush()

Implements abstract java.util.logging.Handler.flush.

Causes a flush on the target Handler.

Note that the current contents of the MemoryHandler buffer are not written out. That requires a "push".

Annotations

@Override

getPushLevel back to summary

getPushLevel	back to summary
public Level getPushLevel() Get the `pushLevel`. Returns:Level the value of the `pushLevel`

public Level getPushLevel()

Get the pushLevel.

Returns:Level: the value of the pushLevel

init	back to summary
private void init()

isLoggable back to summary

isLoggable	back to summary
public boolean isLoggable(LogRecord record) Overrides java.util.logging.Handler.isLoggable. Check if this `Handler` would actually log a given `LogRecord` into its internal buffer. This method checks if the `LogRecord` has an appropriate level and whether it satisfies any `Filter`. However it does not check whether the `LogRecord` would result in a "push" of the buffer contents. It will return false if the `LogRecord` is null. Parameters record:LogRecord a `LogRecord` (may be null). Returns:boolean true if the `LogRecord` would be logged. Annotations @Override

public boolean isLoggable(LogRecord record)

Overrides java.util.logging.Handler.isLoggable.

Check if this Handler would actually log a given LogRecord into its internal buffer.

This method checks if the LogRecord has an appropriate level and whether it satisfies any Filter. However it does not check whether the LogRecord would result in a "push" of the buffer contents. It will return false if the LogRecord is null.

Parameters

record:LogRecord: a LogRecord (may be null).

Returns:boolean

true if the LogRecord would be logged.

Annotations

@Override

publish back to summary

publish	back to summary
public synchronized void publish(LogRecord record) Implements abstract java.util.logging.Handler.publish. Store a `LogRecord` in an internal buffer. If there is a `Filter`, its `isLoggable` method is called to check if the given log record is loggable. If not we return. Otherwise the given record is copied into an internal circular buffer. Then the record's level property is compared with the `pushLevel`. If the given level is greater than or equal to the `pushLevel` then `push` is called to write all buffered records to the target output `Handler`. Parameters record:LogRecord description of the log event. A null record is silently ignored and is not published Annotations @Override

public synchronized void publish(LogRecord record)

Implements abstract java.util.logging.Handler.publish.

Store a LogRecord in an internal buffer.

If there is a Filter, its isLoggable method is called to check if the given log record is loggable. If not we return. Otherwise the given record is copied into an internal circular buffer. Then the record's level property is compared with the pushLevel. If the given level is greater than or equal to the pushLevel then push is called to write all buffered records to the target output Handler.

Parameters

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

Annotations

@Override

push back to summary

push	back to summary
public synchronized void push() Push any buffered output to the target `Handler`. The buffer is then cleared.

public synchronized void push()

Push any buffered output to the target Handler.

The buffer is then cleared.

setPushLevel back to summary

setPushLevel	back to summary
public synchronized void setPushLevel(Level newLevel) Set the `pushLevel`. After a `LogRecord` is copied into our internal buffer, if its level is greater than or equal to the `pushLevel`, then `push` will be called. Parameters newLevel:Level the new value of the `pushLevel`

public synchronized void setPushLevel(Level newLevel)

Set the pushLevel. After a LogRecord is copied into our internal buffer, if its level is greater than or equal to the pushLevel, then push will be called.

Parameters

newLevel:Level: the new value of the pushLevel

public Class MemoryHandler

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail