Module java.logging

Class MemoryHandler


public class MemoryHandler extends Handler
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., the properties would be:

  • Constructor Details

    • MemoryHandler

      public MemoryHandler()
      Create a MemoryHandler and configure it based on LogManager configuration properties.
    • MemoryHandler

      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.

      target - the Handler to which to publish output.
      size - the number of log records to buffer (must be greater than zero)
      pushLevel - message level to push on
      IllegalArgumentException - if size is <= 0
  • Method Details

    • publish

      public void publish(LogRecord record)
      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.

      Specified by:
      publish in class Handler
      record - description of the log event. A null record is silently ignored and is not published
    • push

      public void push()
      Push any buffered output to the target Handler.

      The buffer is then cleared.

    • flush

      public void 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".

      Specified by:
      flush in class Handler
    • close

      public void close() throws SecurityException
      Close the Handler and free all associated resources. This will also close the target Handler.
      Specified by:
      close in class Handler
      SecurityException - if a security manager exists and if the caller does not have LoggingPermission("control").
    • setPushLevel

      public void setPushLevel(Level newLevel) throws SecurityException
      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.
      newLevel - the new value of the pushLevel
      SecurityException - if a security manager exists and if the caller does not have LoggingPermission("control").
    • getPushLevel

      public Level getPushLevel()
      Get the pushLevel.
      the value of the pushLevel
    • isLoggable

      public boolean isLoggable(LogRecord record)
      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.

      isLoggable in class Handler
      record - a LogRecord (may be null).
      true if the LogRecord would be logged.