The version of Apache log4j used by SoundHelix.

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v1_2_2 :: src / xdocs /

index.xml

<?xml version="1.0"?>
<document>

  <properties>
    <author email="ceki@apache.org">Ceki Gulcu</author>
    <title>Introduction</title>
  </properties>

  <meta name="keywords" content="java, logging, tracing, component, framework, API, log4j"/>


<body>
    <section name="Introduction">

      <p>Inserting log statements into your code is a low-tech method
	for debugging it.  It may also be the only way because
	debuggers are not always available or applicable.  This is
	often the case for distributed applications.</p>

      <p>On the other hand, some people argue that log statements
	pollute source code and decrease legibility. (We believe that
	the contrary is true).  In the Java language where a
	preprocessor is not available, log statements increase the
	size of the code and reduce its speed, even when logging is
	turned off.  Given that a reasonably sized application may
	contain thousands of log statements, speed is of particular
	importance.</p>


      <p>With log4j it is possible to enable logging at runtime
	without modifying the application binary. The log4j package is
	designed so that these statements can remain in shipped code
	without incurring a heavy performance cost. Logging behavior
	can be controlled by editing a configuration file, without
	touching the application binary.</p>

      <p>Logging equips the developer with <i>detailed context</i> for
	application failures. On the other hand, testing provides
	quality assurance and confidence in the application. Logging
	and testing should not be confused. They are
	complementary. When logging is wisely used, it can prove to be
	an essential tool.</p>

      <p>One of the distinctive features of log4j is the notion of
	<i>inheritance</i> in loggers. Using a logger
	<em>hierarchy</em> it is possible to control which log
	statements are output at arbitrarily fine granularity but also
	great ease. This helps reduce the volume of logged output and
	minimize the cost of logging.</p>

      <p>The target of the log output can be a file, an
	<code>OutputStream</code>, a <code>java.io.Writer</code>, a
	remote log4j server, a remote Unix Syslog daemon, or even a NT
	Event logger among many other output targets.</p>

      <p>On a 233 MHz ThinkPad running JDK 1.1.7B, it costs about 46
	nanoseconds to determine if that statement should be logged or
	not. Actual logging is also quite fast, ranging from 79
	microseconds using the SimpleLayout, 164 microseconds using
	the TTCCLayout and around a millisecond when printing
	exceptions. The performance of the PatternLayout is almost as
	good as the dedicated layouts, except that it is a lot more
	flexible.</p>

      <p>The package is being constantly improved thanks to input from
	users and code contributed by authors in the community.
      </p>

    </section>
  </body>
</document>
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