org.apache.log4j.WriterAppender Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.log4j;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.helpers.QuietWriter;
import org.apache.log4j.spi.ErrorHandler;
import org.apache.log4j.spi.LoggingEvent;
// Contibutors: Jens Uwe Pipka
// Ben Sandee
/**
WriterAppender appends log events to a {@link java.io.Writer} or an
{@link java.io.OutputStream} depending on the user's choice.
@author Ceki Gülcü
@since 1.1 */
public class WriterAppender extends AppenderSkeleton {
/**
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 boolean immediateFlush = true;
/**
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 String encoding;
/**
This is the {@link QuietWriter quietWriter} where we will write
to.
*/
protected QuietWriter qw;
/**
This default constructor does nothing. */
public
WriterAppender() {
}
/**
Instantiate a WriterAppender and set the output destination to a
new {@link OutputStreamWriter} initialized with os
as its {@link OutputStream}. */
public
WriterAppender(Layout layout, OutputStream os) {
this(layout, new OutputStreamWriter(os));
}
/**
Instantiate a WriterAppender and set the output destination to
writer.
The writer must have been previously opened by
the user. */
public
WriterAppender(Layout layout, Writer writer) {
this.layout = layout;
this.setWriter(writer);
}
/**
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
void setImmediateFlush(boolean value) {
immediateFlush = value;
}
/**
Returns value of the ImmediateFlush option.
*/
public
boolean getImmediateFlush() {
return immediateFlush;
}
/**
Does nothing.
*/
public
void activateOptions() {
}
/**
This method is called by the {@link AppenderSkeleton#doAppend}
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
void append(LoggingEvent event) {
// Reminder: the nesting of calls is:
//
// doAppend()
// - check threshold
// - filter
// - append();
// - checkEntryConditions();
// - subAppend();
if(!checkEntryConditions()) {
return;
}
subAppend(event);
}
/**
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
boolean checkEntryConditions() {
if(this.closed) {
LogLog.warn("Not allowed to write to a closed appender.");
return false;
}
if(this.qw == null) {
errorHandler.error("No output stream or file set for the appender named ["+
name+"].");
return false;
}
if(this.layout == null) {
errorHandler.error("No layout set for the appender named ["+ name+"].");
return false;
}
return true;
}
/**
Close this appender instance. The underlying stream or writer is
also closed.
Closed appenders cannot be reused.
@see #setWriter
@since 0.8.4 */
public
synchronized
void close() {
if(this.closed)
return;
this.closed = true;
writeFooter();
reset();
}
/**
* Close the underlying {@link java.io.Writer}.
* */
protected void closeWriter() {
if(qw != null) {
try {
qw.close();
} catch(IOException e) {
if (e instanceof InterruptedIOException) {
Thread.currentThread().interrupt();
}
// There is do need to invoke an error handler at this late
// stage.
LogLog.error("Could not close " + qw, e);
}
}
}
/**
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
OutputStreamWriter createWriter(OutputStream os) {
OutputStreamWriter retval = null;
String enc = getEncoding();
if(enc != null) {
try {
retval = new OutputStreamWriter(os, enc);
} catch(IOException e) {
if (e instanceof InterruptedIOException) {
Thread.currentThread().interrupt();
}
LogLog.warn("Error initializing output writer.");
LogLog.warn("Unsupported encoding?");
}
}
if(retval == null) {
retval = new OutputStreamWriter(os);
}
return retval;
}
public String getEncoding() {
return encoding;
}
public void setEncoding(String value) {
encoding = value;
}
/**
Set the {@link ErrorHandler} for this WriterAppender and also the
underlying {@link QuietWriter} if any. */
public synchronized void setErrorHandler(ErrorHandler eh) {
if(eh == null) {
LogLog.warn("You have tried to set a null error-handler.");
} else {
this.errorHandler = eh;
if(this.qw != null) {
this.qw.setErrorHandler(eh);
}
}
}
/**
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.
@param writer An already opened Writer. */
public synchronized void setWriter(Writer writer) {
reset();
this.qw = new QuietWriter(writer, errorHandler);
//this.tp = new TracerPrintWriter(qw);
writeHeader();
}
/**
Actual writing occurs here.
Most subclasses of WriterAppender will need to
override this method.
@since 0.9.0 */
protected
void subAppend(LoggingEvent event) {
this.qw.write(this.layout.format(event));
if(layout.ignoresThrowable()) {
String[] s = event.getThrowableStrRep();
if (s != null) {
int len = s.length;
for(int i = 0; i < len; i++) {
this.qw.write(s[i]);
this.qw.write(Layout.LINE_SEP);
}
}
}
if(shouldFlush(event)) {
this.qw.flush();
}
}
/**
The WriterAppender requires a layout. Hence, this method returns
true.
*/
public
boolean requiresLayout() {
return true;
}
/**
Clear internal references to the writer and other variables.
Subclasses can override this method for an alternate closing
behavior. */
protected
void reset() {
closeWriter();
this.qw = null;
//this.tp = null;
}
/**
Write a footer as produced by the embedded layout's {@link
Layout#getFooter} method. */
protected
void writeFooter() {
if(layout != null) {
String f = layout.getFooter();
if(f != null && this.qw != null) {
this.qw.write(f);
this.qw.flush();
}
}
}
/**
Write a header as produced by the embedded layout's {@link
Layout#getHeader} method. */
protected
void writeHeader() {
if(layout != null) {
String h = layout.getHeader();
if(h != null && this.qw != null)
this.qw.write(h);
}
}
/**
* Determines whether the writer should be flushed after
* this event is written.
*
* @since 1.2.16
*/
protected boolean shouldFlush(final LoggingEvent event) {
return immediateFlush;
}
}