org.apache.log4j

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 Summary

Fields

Modifier and Type	Field and Description
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.

Fields inherited from class org.apache.log4j.AppenderSkeleton

closed, errorHandler, headFilter, layout, name, tailFilter, threshold

Constructor Summary

Constructors

Constructor and Description
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.

Method Summary

Modifier and Type	Method and Description
void	activateOptions() Does nothing.
void	append(LoggingEvent event) This method is called by the AppenderSkeleton.doAppend(org.apache.log4j.spi.LoggingEvent) method.
protected boolean	checkEntryConditions() This method determines if there is a sense in attempting to append.
void	close() Close this appender instance.
protected void	closeWriter() Close the underlying Writer.
protected OutputStreamWriter	createWriter(OutputStream os) Returns an OutputStreamWriter when passed an OutputStream.
String	getEncoding()
boolean	getImmediateFlush() Returns value of the ImmediateFlush option.
boolean	requiresLayout() The WriterAppender requires a layout.
protected void	reset() Clear internal references to the writer and other variables.
void	setEncoding(String value)
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.
void	setWriter(Writer writer) Sets the Writer where the log output will go.
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.
protected void	writeFooter() Write a footer as produced by the embedded layout's Layout.getFooter() method.
protected void	writeHeader() Write a header as produced by the embedded layout's Layout.getHeader() method.

Methods inherited from class org.apache.log4j.AppenderSkeleton

addFilter, clearFilters, doAppend, finalize, getErrorHandler, getFilter, getFirstFilter, getLayout, getName, getThreshold, isAsSevereAsThreshold, setLayout, setName, setThreshold

Methods inherited from class java.lang.Object

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

Field Detail

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 Detail

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 Detail

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:

setWriter(java.io.Writer)

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