public class

WriterAppender

extends AppenderSkeleton
java.lang.Object
   ↳ org.apache.log4j.AppenderSkeleton
     ↳ org.apache.log4j.WriterAppender
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

WriterAppender appends log events to a java.io.Writer or an java.io.OutputStream depending on the user's choice.

Summary

Fields
protected String encoding The encoding to use when writing.
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.
protected QuietWriter qw This is the quietWriter where we will write to.
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Inherited Fields
From class org.apache.log4j.AppenderSkeleton
Public Constructors
WriterAppender()
This default constructor does nothing.
WriterAppender(Layout layout, OutputStream os)
Instantiate a WriterAppender and set the output destination to a new OutputStreamWriter initialized with os as its OutputStream.
WriterAppender(Layout layout, Writer writer)
Instantiate a WriterAppender and set the output destination to writer.
Public Methods
void activateOptions()
Does nothing.
void append(LoggingEvent event)
This method is called by the doAppend(LoggingEvent) method.
synchronized void close()
Close this appender instance.
String getEncoding()
boolean getImmediateFlush()
Returns value of the ImmediateFlush option.
boolean requiresLayout()
The WriterAppender requires a layout.
void setEncoding(String value)
synchronized void setErrorHandler(ErrorHandler eh)
Set the ErrorHandler for this WriterAppender and also the underlying QuietWriter if any.
void setImmediateFlush(boolean value)
If the ImmediateFlush option is set to true, the appender will flush at the end of each write.
synchronized void setWriter(Writer writer)

Sets the Writer where the log output will go.

Protected Methods
boolean checkEntryConditions()
This method determines if there is a sense in attempting to append.
void closeWriter()
Close the underlying java.io.Writer.
OutputStreamWriter createWriter(OutputStream os)
Returns an OutputStreamWriter when passed an OutputStream.
void reset()
Clear internal references to the writer and other variables.
boolean shouldFlush(LoggingEvent event)
Determines whether the writer should be flushed after this event is written.
void subAppend(LoggingEvent event)
Actual writing occurs here.
void writeFooter()
Write a footer as produced by the embedded layout's getFooter() method.
void writeHeader()
Write a header as produced by the embedded layout's getHeader() method.
[Expand]
Inherited Methods
From class org.apache.log4j.AppenderSkeleton
From class java.lang.Object
From interface org.apache.log4j.Appender
From interface org.apache.log4j.spi.OptionHandler

Fields

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.

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.

protected QuietWriter qw

This is the quietWriter where we will write to.

Public Constructors

public WriterAppender ()

This default constructor does nothing.

public WriterAppender (Layout layout, OutputStream os)

Instantiate a WriterAppender and set the output destination to a new OutputStreamWriter initialized with os as its OutputStream.

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.

Public Methods

public void activateOptions ()

Does nothing.

public void append (LoggingEvent event)

This method is called by the doAppend(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.

public synchronized void close ()

Close this appender instance. The underlying stream or writer is also closed.

Closed appenders cannot be reused.

See Also

public String getEncoding ()

public boolean getImmediateFlush ()

Returns value of the ImmediateFlush option.

public boolean requiresLayout ()

The WriterAppender requires a layout. Hence, this method returns true.

public void setEncoding (String value)

public synchronized void setErrorHandler (ErrorHandler eh)

Set the ErrorHandler for this WriterAppender and also the underlying QuietWriter if any.

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.

public synchronized 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.

Protected Methods

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.

protected void closeWriter ()

Close the underlying java.io.Writer.

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.

protected void reset ()

Clear internal references to the writer and other variables. Subclasses can override this method for an alternate closing behavior.

protected boolean shouldFlush (LoggingEvent event)

Determines whether the writer should be flushed after this event is written.

protected void subAppend (LoggingEvent event)

Actual writing occurs here.

Most subclasses of WriterAppender will need to override this method.

protected void writeFooter ()

Write a footer as produced by the embedded layout's getFooter() method.

protected void writeHeader ()

Write a header as produced by the embedded layout's getHeader() method.