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<title>@Log (and friends)</title>
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<div class="header"><a href="../index.html">Project Lombok</a></div>
<h1>@Log (and friends)</h1>
<div class="byline">Captain's Log, stardate 24435.7: "What was that line again?"</div>
<div class="overview">
<h3>Overview</h3>
<p>
<em>NEW in lombok 0.10: </em>You can annotate any class with a log annotation to let lombok generate a logger field.<br />
The logger is named <code>log</code> and the field's type depends on which logger you have selected.
</p><p>
There are six choices available:<br />
<dl>
<dt><code>@CommonsLog</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://commons.apache.org/logging/apidocs/org/apache/commons/logging/Log.html">org.apache.commons.logging.Log</a> <span class="staticfield">log</span> = <a href="http://commons.apache.org/logging/apidocs/org/apache/commons/logging/LogFactory.html#getLog(java.lang.Class)">org.apache.commons.logging.LogFactory.getLog</a>(LogExample.<span class="keyword">class</span>);</code></dd>
<dt><code>@Log</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://download.oracle.com/javase/6/docs/api/java/util/logging/Logger.html">java.util.logging.Logger</a> <span class="staticfield">log</span> = <a href="http://download.oracle.com/javase/6/docs/api/java/util/logging/Logger.html#getLogger(java.lang.String)">java.util.logging.Logger.getLogger</a>(LogExample.<span class="keyword">class</span>.getName());</code></dd>
<dt><code>@Log4j</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Logger.html">org.apache.log4j.Logger</a> <span class="staticfield">log</span> = <a href="http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/Logger.html#getLogger(java.lang.Class)">org.apache.log4j.Logger.getLogger</a>(LogExample.<span class="keyword">class</span>);</code></dd>
<dt><code>@Log4j2</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://logging.apache.org/log4j/2.0/log4j-api/apidocs/org/apache/logging/log4j/Logger.html">org.apache.logging.log4j.Logger</a> <span class="staticfield">log</span> = <a href="http://logging.apache.org/log4j/2.0/log4j-api/apidocs/org/apache/logging/log4j/LogManager.html#getLogger(java.lang.Class)">org.apache.logging.log4j.LogManager.getLogger</a>(LogExample.<span class="keyword">class</span>);</code></dd>
<dt><code>@Slf4j</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://www.slf4j.org/api/org/slf4j/Logger.html">org.slf4j.Logger</a> <span class="staticfield">log</span> = <a href="http://www.slf4j.org/apidocs/org/slf4j/LoggerFactory.html#getLogger(java.lang.Class)">org.slf4j.LoggerFactory.getLogger</a>(LogExample.<span class="keyword">class</span>);</code></dd>
<dt><code>@XSlf4j</code></dt>
<dd>Creates <code><span class="keyword">private static final </span><a href="http://www.slf4j.org/api/org/slf4j/ext/XLogger.html">org.slf4j.ext.XLogger</a> <span class="staticfield">log</span> = <a href="http://www.slf4j.org/apidocs/org/slf4j/ext/XLoggerFactory.html#getXLogger(java.lang.Class)">org.slf4j.ext.XLoggerFactory.getXLogger</a>(LogExample.<span class="keyword">class</span>);</code></dd>
</dl>
</p><p>
By default, the topic (or name) of the logger will be the class name of the class annotated with the <code>@Log</code> annotation. This can be customised by specifying the <code>topic</code> parameter. For example: <code>@XSlf4j(topic="reporting")</code>.
</p>
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<h3>With Lombok</h3>
<div class="snippet">@HTML_PRE@</div>
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<div class="sep"></div>
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<h3>Vanilla Java</h3>
<div class="snippet">@HTML_POST@</div>
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<div class="overview">
<h3>Small print</h3><div class="smallprint">
<p>
If a field called <code>log</code> already exists, a warning will be emitted and no code will be generated.
</p><p>
A future feature of lombok's diverse log annotations is to find calls to the logger field and, if the chosen logging framework supports it and the log level can be compile-time determined from the log call, guard it with an <code>if</code> statement. This way if the log statement ends up being ignored, the potentially expensive calculation of the log string is avoided entirely. This does mean that you should <em>NOT</em> put any side-effects in the expression that you log.
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