Apache Log4j provides the interface that applications should code to and provides the adapter components required for implementers to create a logging implementation.

Bytecode (Java 1.4) for Apache Log4j is provided in a JAR file like log4j-1.2.17.jar.

Source Code files for Apache Log4j are provided in both binary packge like log4j-1.2.17.zip and source package like log4j-1.2.17-sources.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j 1.2.17 below.

⏎ org/apache/log4j/xml/XMLLayout.java

/*
 * 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.
 */

// Contributors:   Mathias Bogaert

package org.apache.log4j.xml;

import org.apache.log4j.Layout;
import org.apache.log4j.helpers.Transform;
import org.apache.log4j.spi.LocationInfo;
import org.apache.log4j.spi.LoggingEvent;

import java.util.Set;
import java.util.Arrays;

/**
 * The output of the XMLLayout consists of a series of log4j:event
 * elements as defined in the <a
 * href="log4j.dtd">log4j.dtd</a>. It does not output a
 * complete well-formed XML file. The output is designed to be
 * included as an <em>external entity</em> in a separate file to form
 * a correct XML file.
 *
 * <p>For example, if <code>abc</code> is the name of the file where
 * the XMLLayout ouput goes, then a well-formed XML file would be:
 *
  <pre>
   &lt;?xml version="1.0" ?&gt;
 
  &lt;!DOCTYPE log4j:eventSet PUBLIC "-//APACHE//DTD LOG4J 1.2//EN" "log4j.dtd" [&lt;!ENTITY data SYSTEM "abc"&gt;]&gt;
 
  &lt;log4j:eventSet version="1.2" xmlns:log4j="http://jakarta.apache.org/log4j/"&gt;
 	&nbsp;&nbsp;&data;
  &lt;/log4j:eventSet&gt;
  </pre>
 
 * <p>This approach enforces the independence of the XMLLayout and the
 * appender where it is embedded.
 *
 * <p>The <code>version</code> attribute helps components to correctly
 * intrepret output generated by XMLLayout. The value of this
 * attribute should be "1.1" for output generated by log4j versions
 * prior to log4j 1.2 (final release) and "1.2" for relase 1.2 and
 * later.
 *
 * Appenders using this layout should have their encoding
 * set to UTF-8 or UTF-16, otherwise events containing
 * non ASCII characters could result in corrupted
 * log files. 
 *
 * @author Ceki  G&uuml;lc&uuml;
 * @since 0.9.0 
 * */
public class XMLLayout extends Layout {

  private  final int DEFAULT_SIZE = 256;
  private final int UPPER_LIMIT = 2048;

  private StringBuffer buf = new StringBuffer(DEFAULT_SIZE);
  private boolean locationInfo = false;
  private boolean properties = false;
 
  /**
   * The <b>LocationInfo</b> option takes a boolean value. By default,
   * it is set to false which means there will be no location
   * information output by this layout. If the the option is set to
   * true, then the file name and line number of the statement at the
   * origin of the log statement will be output.
   *
   * <p>If you are embedding this layout within an {@link
   * org.apache.log4j.net.SMTPAppender} then make sure to set the
   * <b>LocationInfo</b> option of that appender as well.
   * */
  public void setLocationInfo(boolean flag) {
    locationInfo = flag;
  }
  
  /**
     Returns the current value of the <b>LocationInfo</b> option.
   */
  public boolean getLocationInfo() {
    return locationInfo;
  }

    /**
     * Sets whether MDC key-value pairs should be output, default false.
     * @param flag new value.
     * @since 1.2.15
     */
  public void setProperties(final boolean flag) {
      properties = flag;
  }

    /**
     * Gets whether MDC key-value pairs should be output.
     * @return true if MDC key-value pairs are output.
     * @since 1.2.15
     */
  public boolean getProperties() {
      return properties;
  }

  /** No options to activate. */
  public void activateOptions() {
  }


  /**
   * Formats a {@link org.apache.log4j.spi.LoggingEvent} in conformance with the log4j.dtd.
   * */
  public String format(final LoggingEvent event) {

    // Reset working buffer. If the buffer is too large, then we need a new
    // one in order to avoid the penalty of creating a large array.
    if(buf.capacity() > UPPER_LIMIT) {
      buf = new StringBuffer(DEFAULT_SIZE);
    } else {
      buf.setLength(0);
    }
    
    // We yield to the \r\n heresy.

    buf.append("<log4j:event logger=\"");
    buf.append(Transform.escapeTags(event.getLoggerName()));
    buf.append("\" timestamp=\"");
    buf.append(event.timeStamp);
    buf.append("\" level=\"");
    buf.append(Transform.escapeTags(String.valueOf(event.getLevel())));
    buf.append("\" thread=\"");
    buf.append(Transform.escapeTags(event.getThreadName()));
    buf.append("\">\r\n");

    buf.append("<log4j:message><![CDATA[");
    // Append the rendered message. Also make sure to escape any
    // existing CDATA sections.
    Transform.appendEscapingCDATA(buf, event.getRenderedMessage());
    buf.append("]]></log4j:message>\r\n");       
    
    String ndc = event.getNDC();
    if(ndc != null) {
      buf.append("<log4j:NDC><![CDATA[");
      Transform.appendEscapingCDATA(buf, ndc);
      buf.append("]]></log4j:NDC>\r\n");       
    }
    
    String[] s = event.getThrowableStrRep();
    if(s != null) {
      buf.append("<log4j:throwable><![CDATA[");
      for(int i = 0; i < s.length; i++) {
          Transform.appendEscapingCDATA(buf, s[i]);
	      buf.append("\r\n");
      }
      buf.append("]]></log4j:throwable>\r\n");
    }
    
    if(locationInfo) { 
      LocationInfo locationInfo = event.getLocationInformation();	
      buf.append("<log4j:locationInfo class=\"");
      buf.append(Transform.escapeTags(locationInfo.getClassName()));
      buf.append("\" method=\"");
      buf.append(Transform.escapeTags(locationInfo.getMethodName()));
      buf.append("\" file=\"");
      buf.append(Transform.escapeTags(locationInfo.getFileName()));
      buf.append("\" line=\"");
      buf.append(locationInfo.getLineNumber());
      buf.append("\"/>\r\n");
    }

    if (properties) {
        Set keySet = event.getPropertyKeySet();
        if (keySet.size() > 0) {
            buf.append("<log4j:properties>\r\n");
            Object[] keys = keySet.toArray();
            Arrays.sort(keys);
            for (int i = 0; i < keys.length; i++) {
                String key = keys[i].toString();
                Object val = event.getMDC(key);
                if (val != null) {
                    buf.append("<log4j:data name=\"");
                    buf.append(Transform.escapeTags(key));
                    buf.append("\" value=\"");
                    buf.append(Transform.escapeTags(String.valueOf(val)));
                    buf.append("\"/>\r\n");
                }
            }
            buf.append("</log4j:properties>\r\n");
        }
    }
    
    buf.append("</log4j:event>\r\n\r\n");
    
    return buf.toString();
  }
  
  /**
     The XMLLayout prints and does not ignore exceptions. Hence the
     return value <code>false</code>.
  */
  public boolean ignoresThrowable() {
    return false;
  }
}

⏎ org/apache/log4j/xml/XMLLayout.java

Or download all of them as a single archive file:

File name: log4j-1.2.17-sources.jar
File size: 481200 bytes
Release date: 2012-05-06
Download 

⇒ Download and Install apache-log4j-1.2.15.zip

⇐ Download and Install log4j-1.2.17.zip

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