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<h1 id="logging">Logging</h1>
<h2 id="logging-support">Logging support</h2>
<blockquote>
<p>As from Struts 2.5 version, the logging layer is deprecated and Struts uses Log4j2
The logging layer will be dropped with the next major release.</p>
</blockquote>
<p>XWork provides its own layer to support logging - it allows to use many different implementations.</p>
<p>Currently XWork provides support for the following libraries (in that order base on classpath discovery):</p>
<ul>
<li>Commons Logging</li>
<li><a href="http://www.slf4j.org/">SLF4J</a></li>
<li><a href="http://logging.apache.org/log4j/2.x/">Log4j2</a></li>
<li>JDK Logger</li>
</ul>
<h2 id="usage">Usage</h2>
<p>To use given type of library add it as a Maven dependency or drop into WEB-INF/lib folder. XWork LoggerFactory class will
use given logging provider if available.</p>
<p>To add logging to your application simply declare a Logger as follow:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.Logger</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.LoggerFactory</span><span class="o">;</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">MyAction</span> <span class="o">{</span>
<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">Logger</span> <span class="n">LOG</span> <span class="o">=</span> <span class="n">LoggerFactory</span><span class="o">.</span><span class="na">getLogger</span><span class="o">(</span><span class="n">MyAction</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
<span class="kd">private</span> <span class="n">String</span> <span class="n">userName</span><span class="o">;</span>
<span class="kd">public</span> <span class="n">String</span> <span class="nf">execute</span><span class="o">()</span> <span class="o">{</span>
<span class="n">LOG</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">"MyAction executed with UserName [#0]"</span><span class="o">,</span> <span class="n">userName</span><span class="o">);</span>
<span class="k">return</span> <span class="s">"success"</span><span class="o">;</span>
<span class="o">}</span>
<span class="c1">// getter / setter</span>
<span class="o">}</span>
</code></pre></div></div>
<h2 id="implementing-my-own-factory">Implementing my own factory</h2>
<p>You plug in your own logging solution, simple extend LoggerFactory class and provide a delegate which implements Logger
interface, like below:</p>
<p><strong>JdkLoggerFactory which adds support for JDK logging</strong></p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.Logger</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.LoggerFactory</span><span class="o">;</span>
<span class="cm">/**
* Creates jdk loggers
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">JdkLoggerFactory</span> <span class="kd">extends</span> <span class="n">LoggerFactory</span> <span class="o">{</span>
<span class="nd">@Override</span>
<span class="kd">protected</span> <span class="n">Logger</span> <span class="nf">getLoggerImpl</span><span class="o">(</span><span class="n">Class</span><span class="o">&lt;?&gt;</span> <span class="n">cls</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="k">new</span> <span class="nf">JdkLogger</span><span class="o">(</span><span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">logging</span><span class="o">.</span><span class="na">Logger</span><span class="o">.</span><span class="na">getLogger</span><span class="o">(</span><span class="n">cls</span><span class="o">.</span><span class="na">getName</span><span class="o">()));</span>
<span class="o">}</span>
<span class="nd">@Override</span>
<span class="kd">protected</span> <span class="n">Logger</span> <span class="nf">getLoggerImpl</span><span class="o">(</span><span class="n">String</span> <span class="n">name</span><span class="o">)</span> <span class="o">{</span>
<span class="k">return</span> <span class="k">new</span> <span class="nf">JdkLogger</span><span class="o">(</span><span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">logging</span><span class="o">.</span><span class="na">Logger</span><span class="o">.</span><span class="na">getLogger</span><span class="o">(</span><span class="n">name</span><span class="o">));</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p><strong>JdkLogger is a wrapper around java.util.logging.Logger and implements Logger interface</strong></p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.Logger</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">com.opensymphony.xwork2.util.logging.LoggerUtils</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">java.util.logging.Level</span><span class="o">;</span>
<span class="cm">/**
* Delegates to jdk logger. Maps fatal to Level.SEVERE along with error.
*/</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">JdkLogger</span> <span class="kd">implements</span> <span class="n">Logger</span> <span class="o">{</span>
<span class="kd">private</span> <span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">logging</span><span class="o">.</span><span class="na">Logger</span> <span class="n">log</span><span class="o">;</span>
<span class="kd">public</span> <span class="nf">JdkLogger</span><span class="o">(</span><span class="n">java</span><span class="o">.</span><span class="na">util</span><span class="o">.</span><span class="na">logging</span><span class="o">.</span><span class="na">Logger</span> <span class="n">log</span><span class="o">)</span> <span class="o">{</span>
<span class="k">this</span><span class="o">.</span><span class="na">log</span> <span class="o">=</span> <span class="n">log</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">error</span><span class="o">(</span><span class="n">String</span> <span class="n">msg</span><span class="o">,</span> <span class="n">String</span><span class="o">...</span> <span class="n">args</span><span class="o">)</span> <span class="o">{</span>
<span class="n">log</span><span class="o">.</span><span class="na">log</span><span class="o">(</span><span class="n">Level</span><span class="o">.</span><span class="na">SEVERE</span><span class="o">,</span> <span class="n">LoggerUtils</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="n">msg</span><span class="o">,</span> <span class="n">args</span><span class="o">));</span>
<span class="o">}</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">error</span><span class="o">(</span><span class="n">String</span> <span class="n">msg</span><span class="o">,</span> <span class="n">Throwable</span> <span class="n">ex</span><span class="o">,</span> <span class="n">String</span><span class="o">...</span> <span class="n">args</span><span class="o">)</span> <span class="o">{</span>
<span class="n">log</span><span class="o">.</span><span class="na">log</span><span class="o">(</span><span class="n">Level</span><span class="o">.</span><span class="na">SEVERE</span><span class="o">,</span> <span class="n">LoggerUtils</span><span class="o">.</span><span class="na">format</span><span class="o">(</span><span class="n">msg</span><span class="o">,</span> <span class="n">args</span><span class="o">),</span> <span class="n">ex</span><span class="o">);</span>
<span class="o">}</span>
<span class="o">...</span>
<span class="o">}</span>
</code></pre></div></div>
<p>Check <a href="http://struts.apache.org/struts-core/apidocs/com/opensymphony/xwork2/util/logging/package-summary.html">the source code</a>
to see more details.</p>
<h2 id="defining-which-factory-to-use">Defining which factory to use</h2>
<p>Now you must tell XWork/Struts2 to use your implementation, just define system property like below:</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>-Dxwork.loggerFactory=com.demo.MyLoggerFactory
</code></pre></div></div>
<p>you can use the same to explicit tell the framework which implementation to use and don’t depend on class discovery, eg.:</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>-Dxwork.loggerFactory=com.opensymphony.xwork2.util.logging.slf4j.Slf4jLoggerFactory
</code></pre></div></div>
<p>or</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>-Dxwork.loggerFactory=com.opensymphony.xwork2.util.logging.log4j2.Log4j2LoggerFactory
</code></pre></div></div>
<p>will enable Slf4j or Log4j2 even if there is commons-logging on classpath available (commons-logging is the first
LoggerFactory to look for).</p>
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