Class WriterAppender

java.lang.Object
org.apache.log4j.AppenderSkeleton
org.apache.log4j.WriterAppender
All Implemented Interfaces:
Appender, OptionHandler
Direct Known Subclasses:
ConsoleAppender, FileAppender

public class WriterAppender extends AppenderSkeleton
WriterAppender appends log events to a Writer or an OutputStream depending on the user's choice.
Since:
1.1
Author:
Ceki Gülcü
  • Field Details

    • immediateFlush

      protected boolean immediateFlush
      Immediate flush means that the underlying writer or output stream will be flushed at the end of each append operation unless shouldFlush() is overridden. Immediate flush is slower but ensures that each append request is actually written. If immediateFlush is set to false, then there is a good chance that the last few logs events are not actually written to persistent media if and when the application crashes.

      The immediateFlush variable is set to true by default.

    • encoding

      protected String encoding
      The encoding to use when writing.

      The encoding variable is set to null by default which results in the utilization of the system's default encoding.

    • qw

      protected QuietWriter qw
      This is the quietWriter where we will write to.
  • Constructor Details

    • WriterAppender

      public WriterAppender()
      This default constructor does nothing.
    • WriterAppender

      public WriterAppender(Layout layout, OutputStream os)
      Instantiate a WriterAppender and set the output destination to a new OutputStreamWriter initialized with os as its OutputStream.
    • WriterAppender

      public WriterAppender(Layout layout, Writer writer)
      Instantiate a WriterAppender and set the output destination to writer.

      The writer must have been previously opened by the user.

  • Method Details

    • setImmediateFlush

      public void setImmediateFlush(boolean value)
      If the ImmediateFlush option is set to true, the appender will flush at the end of each write. This is the default behavior. If the option is set to false, then the underlying stream can defer writing to physical medium to a later time.

      Avoiding the flush operation at the end of each append results in a performance gain of 10 to 20 percent. However, there is safety tradeoff involved in skipping flushing. Indeed, when flushing is skipped, then it is likely that the last few log events will not be recorded on disk when the application exits. This is a high price to pay even for a 20% performance gain.

    • getImmediateFlush

      public boolean getImmediateFlush()
      Returns value of the ImmediateFlush option.
    • activateOptions

      public void activateOptions()
      Does nothing.
      Specified by:
      activateOptions in interface OptionHandler
      Overrides:
      activateOptions in class AppenderSkeleton
    • append

      public void append(LoggingEvent event)
      This method is called by the AppenderSkeleton.doAppend(org.apache.log4j.spi.LoggingEvent) method.

      If the output stream exists and is writable then write a log statement to the output stream. Otherwise, write a single warning message to System.err.

      The format of the output will depend on this appender's layout.

      Specified by:
      append in class AppenderSkeleton
    • checkEntryConditions

      protected boolean checkEntryConditions()
      This method determines if there is a sense in attempting to append.

      It checks whether there is a set output target and also if there is a set layout. If these checks fail, then the boolean value false is returned.

    • close

      public void close()
      Close this appender instance. The underlying stream or writer is also closed.

      Closed appenders cannot be reused.

      Since:
      0.8.4
      See Also:
    • closeWriter

      protected void closeWriter()
      Close the underlying Writer.
    • createWriter

      protected OutputStreamWriter createWriter(OutputStream os)
      Returns an OutputStreamWriter when passed an OutputStream. The encoding used will depend on the value of the encoding property. If the encoding value is specified incorrectly the writer will be opened using the default system encoding (an error message will be printed to the loglog.
    • getEncoding

      public String getEncoding()
    • setEncoding

      public void setEncoding(String value)
    • setErrorHandler

      public void setErrorHandler(ErrorHandler eh)
      Set the ErrorHandler for this WriterAppender and also the underlying QuietWriter if any.
      Specified by:
      setErrorHandler in interface Appender
      Overrides:
      setErrorHandler in class AppenderSkeleton
    • setWriter

      public void setWriter(Writer writer)

      Sets the Writer where the log output will go. The specified Writer must be opened by the user and be writable.

      The java.io.Writer will be closed when the appender instance is closed.

      WARNING: Logging to an unopened Writer will fail.

      Parameters:
      writer - An already opened Writer.
    • subAppend

      protected void subAppend(LoggingEvent event)
      Actual writing occurs here.

      Most subclasses of WriterAppender will need to override this method.

      Since:
      0.9.0
    • requiresLayout

      public boolean requiresLayout()
      The WriterAppender requires a layout. Hence, this method returns true.
    • reset

      protected void reset()
      Clear internal references to the writer and other variables. Subclasses can override this method for an alternate closing behavior.
    • writeFooter

      protected void writeFooter()
      Write a footer as produced by the embedded layout's Layout.getFooter() method.
    • writeHeader

      protected void writeHeader()
      Write a header as produced by the embedded layout's Layout.getHeader() method.
    • shouldFlush

      protected boolean shouldFlush(LoggingEvent event)
      Determines whether the writer should be flushed after this event is written.
      Since:
      1.2.16