The version of Apache log4j used by SoundHelix.
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:: docs
/
ugli.html
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<title>Log4j project - Universal and Generic Logging Interface (UGLI) </title>
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<h1>Universal and Generic Logging Interface (UGLI)</h1>
<p>The Universal and Generic Logging Interface or UGLI is
intended to serve as a simple abstraction of various logging
APIs allowing to plug in the desired implementation at
deployment time. Note that log4j version 1.3 and later support
UGLI directly. Log4j is implemented in terms of the UGLI
interfaces.
</p>
<h2>Typical usage pattern</h2>
<pre class="source">
1: <b>import org.apache.ugli.ULogger;</b>
2: <b>import org.apache.ugli.LoggerFactory;</b>
3:
4: public class Wombat {
5:
6: <b>final ULogger logger = LoggerFactory.getLogger(Wombat.class);</b>
7: Integer t;
8: Integer oldT;
9:
10: public void setTemperature(Integer temparature) {
11:
12: oldT = t;
13: t = temperature;
14:
15: <b>logger.debug("Temperature set to {}. Old temperature was {}.", t, oldT);</b>
16:
17: if(temperature.intValue() > 50) {
18: <b>logger.info("Temperature has risen above 50 degrees".);</b>
19: }
20: }
21: }
</pre>
<p>The example above illustrates the typical usage pattern for
UGLI. Note the use of parameterized log messages on line 15. See
the question <a href="http://logging.apache.org/log4j/docs/faq.html#2.3">
"What is the fastest way of (not) logging?"</a> in the log4j
FAQ for more details.
</p>
<h2>Swapping implementations at deployment time</h2>
<p>UGLI currently supports four implementations, namely, NOP,
Simple, JDK 1.4 logging and log4j. Log4j 1.3 ships with four
jar files <em>ugli-nop.jar</em>, <em>ugli-simple.jar</em>,
<em>ugli-jdk14.jar</em> and <em>log4j.jar</em>. Each of these
jar files are hardwired <em>at compile-time</em> to use just one
implementation, that is NOP, Simple, JDK 1.4 logging and log4j,
respectively.
</p>
<p>Small applications where configuring log4j can be somewhat
of an overkill can drop in <em>ugli-simple.jar</em> in place
of <em>log4j.jar</em>.
</p>
<p>Authors of widely-distributed components and libraries may
code against the UGLI interface in order to avoid imposing an
logging API implementation on the end-user. At deployment
time, the end-user may choose the desired logging API
implementation by inserting the corresponding jar file in her
classpath. This stupid, simple but robust approach avoids many
of the painful bugs associated with dynamic discovery
processes. Life is too short to be spending it hunting down
class loader problems.
</p>
<h2>Simplicity</h2>
<p>The UGLI interfaces and their various adapters are
extremely simple. Most developers familiar with the Java
language should be able to read and fully understand the code
in less than one hour.
</p>
<p>As noted earlier, UGLI does not rely on any classloader
tricks. Every variant of <em>ugli-<impl>.jar</em> is
statically hardwired (at compile time) to use one specific
implementation. Thus, UGLI suffers none of the <a href="http://www.qos.ch/logging/classloader.jsp">class loader
problems observed when using JCL</a>.</p>
<p>We hope that simplicity of the UGLI interfaces and the
deployment model will make it easy for developers of other
logging APIs to conform to the UGLI model.
</p>
<h2>Built-in support in log4j</h2>
<p>The <code>Logger</code> class in log4j directly implements
UGLI's <code>ULogger</code> interface. Moreover, log4j makes
extensive use of UGLI internally.
</p>
<p>Log4j's built-in support for UGLI means that the adapter
for log4j does not need to wrap log4j objects in order to make
them conform to UGLI's <code>ULogger</code> interface. A log4j
<code>Logger</code> <em>is</em> a <code>ULogger</code>. Thus,
using UGLI in conjunction with log4j involves strictly zero
memory overhead and near-zero computational overhead. The
computational overhead is so small as to be unobservable.
</p>
<h2>Where can I get UGLI?</h2>
<p>UGLI ships with log4j version 1.3alpha-6 and later.</p>
<h2>Summary</h2>
<table class="ls" cellspacing="4" cellpadding="4">
<tr>
<th align="left">Advantage</th>
<th align="left">Description</th>
</tr>
<tr>
<td>Fail-safe operation</td>
<td>Assuming the appropriate jar file is available on the
classpath, under no circumstances will UGLI cause your
application to fail. This is because no UGLI class loaded
in memory will <em>ever</em> throw an exception.
<p>Contrast this with
<code>LogConfigurationException</code> thrown by
commons-logging which will cause your otherwise
functioning application to fail. Commons-logging will
throw a <code>LogConfigurationException</code> in case the
<a href="http://jakarta.apache.org/commons/logging/api/org/apache/commons/logging/Log.html">Log</a>
interface and its dynamically discovered implementation
are loaded by different class loaders.
</p>
</td>
</tr>
<tr>
<td>Swappable logging API implementations</td>
<td>The desired logging API can be plugged in at
deployment time by inserting the appropriate jar file on
the classpath.
</td>
</tr>
<tr>
<td>Adapter implementations for the most popular APIs
</td>
<td>UGLI supports the most popular logging APIs, namely
log4j, JDK 1.4 logging, Simple logging and NOP.
</td>
</tr>
<tr>
<td>Support for parameterized log messages</td>
<td>All UGLI adapters support parameterized log messages.</td>
</tr>
<tr>
<td>Built-in support in log4j</td>
<td>Log4j's built-in support for UGLI directly translates
into smaller memory footprint and better CPU efficiency.
</td>
</tr>
</table>
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