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What this is

This file is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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The source code

 * Copyright (C) The Apache Software Foundation. All rights reserved.
 * This software is published under the terms of the Apache Software
 * License version 1.1, a copy of which has been included with this
 * distribution in the LICENSE.txt file.  */

package org.apache.log4j;


import org.apache.log4j.spi.ErrorHandler;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.helpers.QuietWriter;
import org.apache.log4j.helpers.LogLog;

// Contibutors: Jens Uwe Pipka 
//              Ben Sandee

   WriterAppender appends log events to a {@link} or an
   {@link} 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. 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 opening an InputStream.

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}. * */ protected void closeWriter() { if(qw != null) { try { qw.close(); } catch(IOException e) { // 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) { 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 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); // = 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(this.immediateFlush) { 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; // = 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); } } }

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