Source code: org/apache/log4j/PatternLayout.java

   /*
    * 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 file.
    */
   
   package org.apache.log4j;
  
  import org.apache.log4j.Layout;
  import org.apache.log4j.spi.LoggingEvent;
  import org.apache.log4j.helpers.PatternParser;
  import org.apache.log4j.helpers.PatternConverter;
  
  
  // Contributors:   Nelson Minar <nelson@monkey.org>
  //                 Anders Kristensen <akristensen@dynamicsoft.com>
  
  /**
  
     A flexible layout configurable with pattern string.
  
     <p>The goal of this class is to {@link #format format} a {@link
     LoggingEvent} and return the results as a String. The results
     depend on the <em>conversion pattern</em>.
  
     <p>The conversion pattern is closely related to the conversion
     pattern of the printf function in C. A conversion pattern is
     composed of literal text and format control expressions called
     <em>conversion specifiers</em>.
  
     <p><i>You are free to insert any literal text within the conversion
     pattern.</i>
  
     <p>Each conversion specifier starts with a percent sign (%) and is
     followed by optional <em>format modifiers</em> and a <em>conversion
     character</em>. The conversion character specifies the type of
     data, e.g. category, priority, date, thread name. The format
     modifiers control such things as field width, padding, left and
     right justification. The following is a simple example.
  
     <p>Let the conversion pattern be <b>"%-5p [%t]: %m%n"</b> and assume
     that the log4j environment was set to use a PatternLayout. Then the
     statements
     <pre>
     Category root = Category.getRoot();
     root.debug("Message 1");
     root.warn("Message 2");
     </pre>
     would yield the output
     <pre>
     DEBUG [main]: Message 1
     WARN  [main]: Message 2
     </pre>
  
     <p>Note that there is no explicit separator between text and
     conversion specifiers. The pattern parser knows when it has reached
     the end of a conversion specifier when it reads a conversion
     character. In the example above the conversion specifier
     <b>%-5p</b> means the priority of the logging event should be left
     justified to a width of five characters.
  
     The recognized conversion characters are
  
     <p>
     <table border="1" CELLPADDING="8">
     <th>Conversion Character</th>
     <th>Effect</th>
  
     <tr>
       <td align=center><b>c</b></td>
  
       <td>Used to output the category of the logging event. The
       category conversion specifier can be optionally followed by
       <em>precision specifier</em>, that is a decimal constant in
       brackets.
  
       <p>If a precision specifier is given, then only the corresponding
       number of right most components of the category name will be
       printed. By default the category name is printed in full.
  
       <p>For example, for the category name "a.b.c" the pattern
       <b>%c{2}</b> will output "b.c".
  
       </td>
     </tr>
  
     <tr>
       <td align=center><b>C</b></td>
  
       <td>Used to output the fully qualified class name of the caller
       issuing the logging request. This conversion specifier
       can be optionally followed by <em>precision specifier</em>, that
       is a decimal constant in brackets.
  
       <p>If a precision specifier is given, then only the corresponding
       number of right most components of the class name will be
       printed. By default the class name is output in fully qualified form.
 
      <p>For example, for the class name "org.apache.xyz.SomeClass", the
      pattern <b>%C{1}</b> will output "SomeClass".
 
      <p><b>WARNING</b> Generating the caller class information is
      slow. Thus, it's use should be avoided unless execution speed is
      not an issue.
 
      </td>
      </tr>
 
    <tr> <td align=center><b>d</b></td> <td>Used to output the date of
    the logging event. The date conversion specifier may be
    followed by a <em>date format specifier</em> enclosed between
    braces. For example, <b>%d{HH:mm:ss,SSS}</b> or
    <b>%d{dd&nbsp;MMM&nbsp;yyyy&nbsp;HH:mm:ss,SSS}</b>.  If no
    date format specifier is given then ISO8601 format is
    assumed.
 
    <p>The date format specifier admits the same syntax as the
    time pattern string of the {@link
    java.text.SimpleDateFormat}. Although part of the standard
    JDK, the performance of <code>SimpleDateFormat</code> is
    quite poor.
 
    <p>For better results it is recommended to use the log4j date
    formatters. These can be specified using one of the strings
    "ABSOLUTE", "DATE" and "ISO8601" for specifying {@link
    org.apache.log4j.helpers.AbsoluteTimeDateFormat
    AbsoluteTimeDateFormat}, {@link
    org.apache.log4j.helpers.DateTimeDateFormat DateTimeDateFormat}
    and respectively {@link
    org.apache.log4j.helpers.ISO8601DateFormat
    ISO8601DateFormat}. For example, <b>%d{ISO8601}</b> or
    <b>%d{ABSOLUTE}</b>.
 
    <p>These dedicated date formatters perform significantly
    better than {@link java.text.SimpleDateFormat}.
      </td>
    </tr>
 
    <tr>
    <td align=center><b>F</b></td>
 
    <td>Used to output the file name where the logging request was
    issued.
 
    <p><b>WARNING</b> Generating caller location information is
    extremely slow. It's use should be avoided unless execution speed
    is not an issue.
 
    </tr>
 
    <tr>
    <td align=center><b>l</b></td>
 
      <td>Used to output location information of the caller which generated
      the logging event.
 
      <p>The location information depends on the JVM implementation but
      usually consists of the fully qualified name of the calling
      method followed by the callers source the file name and line
      number between parentheses.
 
      <p>The location information can be very useful. However, it's
      generation is <em>extremely</em> slow. It's use should be avoided
      unless execution speed is not an issue.
 
      </td>
    </tr>
 
    <tr>
    <td align=center><b>L</b></td>
 
    <td>Used to output the line number from where the logging request
    was issued.
 
    <p><b>WARNING</b> Generating caller location information is
    extremely slow. It's use should be avoided unless execution speed
    is not an issue.
 
    </tr>
 
 
    <tr>
      <td align=center><b>m</b></td>
      <td>Used to output the application supplied message associated with
      the logging event.</td>
    </tr>
 
    <tr>
    <td align=center><b>M</b></td>
 
    <td>Used to output the method name where the logging request was
    issued.
 
    <p><b>WARNING</b> Generating caller location information is
    extremely slow. It's use should be avoided unless execution speed
    is not an issue.
 
    </tr>
 
    <tr>
      <td align=center><b>n</b></td>
 
      <td>Outputs the platform dependent line separator character or
      characters.
 
      <p>This conversion character offers practically the same
      performance as using non-portable line separator strings such as
      "\n", or "\r\n". Thus, it is the preferred way of specifying a
      line separator.
 
 
    </tr>
 
    <tr>
      <td align=center><b>p</b></td>
      <td>Used to output the priority of the logging event.</td>
    </tr>
 
    <tr>
 
      <td align=center><b>r</b></td>
 
      <td>Used to output the number of milliseconds elapsed since the start
      of the application until the creation of the logging event.</td>
    </tr>
 
 
    <tr>
      <td align=center><b>t</b></td>
 
      <td>Used to output the name of the thread that generated the
      logging event.</td>
 
    </tr>
 
    <tr>
 
      <td align=center><b>x</b></td>
 
      <td>Used to output the NDC (nested diagnostic context) associated
      with the thread that generated the logging event.
      </td>
    </tr>
 
 
    <tr>
      <td align=center><b>X</b></td>
 
      <td> 
      
      <p>Used to output the MDC (mapped diagnostic context) associated
      with the thread that generated the logging event. The <b>X</b>
      conversion character <em>must</em> be followed by the key for the
      map placed between braces, as in <b>%X{clientNumber}</b> where
      <code>clientNumber</code> is the key. The value in the MDC
      corresponding to the key will be output.</p>
      
      <p>See {@link MDC} class for more details.
      </p>
      
      </td>
    </tr>
 
    <tr>
 
      <td align=center><b>%</b></td>
 
      <td>The sequence %% outputs a single percent sign.
      </td>
    </tr>
 
    </table>
 
    <p>By default the relevant information is output as is. However,
    with the aid of format modifiers it is possible to change the
    minimum field width, the maximum field width and justification.
 
    <p>The optional format modifier is placed between the percent sign
    and the conversion character.
 
    <p>The first optional format modifier is the <em>left justification
    flag</em> which is just the minus (-) character. Then comes the
    optional <em>minimum field width</em> modifier. This is a decimal
    constant that represents the minimum number of characters to
    output. If the data item requires fewer characters, it is padded on
    either the left or the right until the minimum width is
    reached. The default is to pad on the left (right justify) but you
    can specify right padding with the left justification flag. The
    padding character is space. If the data item is larger than the
    minimum field width, the field is expanded to accommodate the
    data. The value is never truncated.
 
    <p>This behavior can be changed using the <em>maximum field
    width</em> modifier which is designated by a period followed by a
    decimal constant. If the data item is longer than the maximum
    field, then the extra characters are removed from the
    <em>beginning</em> of the data item and not from the end. For
    example, it the maximum field width is eight and the data item is
    ten characters long, then the first two characters of the data item
    are dropped. This behavior deviates from the printf function in C
    where truncation is done from the end.
 
    <p>Below are various format modifier examples for the category
    conversion specifier.
 
    <p>
    <TABLE BORDER=1 CELLPADDING=8>
    <th>Format modifier
    <th>left justify
    <th>minimum width
    <th>maximum width
    <th>comment
 
    <tr>
    <td align=center>%20c</td>
    <td align=center>false</td>
    <td align=center>20</td>
    <td align=center>none</td>
 
    <td>Left pad with spaces if the category name is less than 20
    characters long.
 
    <tr> <td align=center>%-20c</td> <td align=center>true</td> <td
    align=center>20</td> <td align=center>none</td> <td>Right pad with
    spaces if the category name is less than 20 characters long.
 
    <tr>
    <td align=center>%.30c</td>
    <td align=center>NA</td>
    <td align=center>none</td>
    <td align=center>30</td>
 
    <td>Truncate from the beginning if the category name is longer than 30
    characters.
 
    <tr>
    <td align=center>%20.30c</td>
    <td align=center>false</td>
    <td align=center>20</td>
    <td align=center>30</td>
 
    <td>Left pad with spaces if the category name is shorter than 20
    characters. However, if category name is longer than 30 characters,
    then truncate from the beginning.
 
    <tr>
    <td align=center>%-20.30c</td>
    <td align=center>true</td>
    <td align=center>20</td>
    <td align=center>30</td>
 
    <td>Right pad with spaces if the category name is shorter than 20
    characters. However, if category name is longer than 30 characters,
    then truncate from the beginning.
 
    </table>
 
    <p>Below are some examples of conversion patterns.
 
    <dl>
 
    <p><dt><b>%r [%t] %-5p %c %x - %m\n</b>
    <p><dd>This is essentially the TTCC layout.
 
    <p><dt><b>%-6r [%15.15t] %-5p %30.30c %x - %m\n</b>
 
    <p><dd>Similar to the TTCC layout except that the relative time is
    right padded if less than 6 digits, thread name is right padded if
    less than 15 characters and truncated if longer and the category
    name is left padded if shorter than 30 characters and truncated if
    longer.
 
   </dl>
 
    <p>The above text is largely inspired from Peter A. Darnell and
    Philip E. Margolis' highly recommended book "C -- a Software
    Engineering Approach", ISBN 0-387-97389-3.
 
    @author <a href="mailto:cakalijp@Maritz.com">James P. Cakalic</a>
    @author Ceki G&uuml;lc&uuml;
 
 
    @since 0.8.2 */
 public class PatternLayout extends Layout {
 
 
   /** Default pattern string for log output. Currently set to the
       string <b>"%m%n"</b> which just prints the application supplied
       message. */
   public final static String DEFAULT_CONVERSION_PATTERN ="%m%n";
 
   /** A conversion pattern equivalent to the TTCCCLayout.
       Current value is <b>%r [%t] %p %c %x - %m%n</b>. */
   public final static String TTCC_CONVERSION_PATTERN
                                              = "%r [%t] %p %c %x - %m%n";
 
 
   protected final int BUF_SIZE = 256;
   protected final int MAX_CAPACITY = 1024;
 
 
   // output buffer appended to when format() is invoked
   private StringBuffer sbuf = new StringBuffer(BUF_SIZE);
 
   private String pattern;
 
   private PatternConverter head;
 
   private String timezone;
 
   /**
      Constructs a PatternLayout using the DEFAULT_LAYOUT_PATTERN.
 
      The default pattern just produces the application supplied message.
   */
   public PatternLayout() {
     this(DEFAULT_CONVERSION_PATTERN);
   }
 
   /**
      Constructs a PatternLayout using the supplied conversion pattern.
   */
   public PatternLayout(String pattern) {
     this.pattern = pattern;
     head = createPatternParser((pattern == null) ? DEFAULT_CONVERSION_PATTERN :
            pattern).parse();
   }
 
    /**
      Set the <b>ConversionPattern</b> option. This is the string which
      controls formatting and consists of a mix of literal content and
      conversion specifiers.
    */
   public
   void setConversionPattern(String conversionPattern) {
     pattern = conversionPattern;
     head = createPatternParser(conversionPattern).parse();
   }
 
   /**
      Returns the value of the <b>ConversionPattern</b> option.
    */
   public
   String getConversionPattern() {
     return pattern;
   }
 
   /**
      Does not do anything as options become effective
   */
   public
   void activateOptions() {
     // nothing to do.
   }
 
  /**
      The PatternLayout does not handle the throwable contained within
      {@link LoggingEvent LoggingEvents}. Thus, it returns
      <code>true</code>.
 
      @since 0.8.4 */
   public
   boolean ignoresThrowable() {
     return true;
   }
 
   /**
     Returns PatternParser used to parse the conversion string. Subclasses
     may override this to return a subclass of PatternParser which recognize
     custom conversion characters.
 
     @since 0.9.0
   */
   protected PatternParser createPatternParser(String pattern) {
     return new PatternParser(pattern);
   }
 
 
   /**
      Produces a formatted string as specified by the conversion pattern.
   */
   public String format(LoggingEvent event) {
     // Reset working stringbuffer
     if(sbuf.capacity() > MAX_CAPACITY) {
       sbuf = new StringBuffer(BUF_SIZE);
     } else {
       sbuf.setLength(0);
     }
 
     PatternConverter c = head;
 
     while(c != null) {
       c.format(sbuf, event);
       c = c.next;
     }
     return sbuf.toString();
   }
 }