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<div class="subTitle">org.apache.log4j</div>
<h2 title="Class NDC" class="title">Class NDC</h2>
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<pre>public final class <a href="../../../src-html/org/apache/log4j/NDC.html#line.24">NDC</a>
extends <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre>
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<h3>Method Summary</h3>
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<caption><span>Methods</span><span class="tabEnd">&nbsp;</span></caption>
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<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
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<tr class="altColor">
<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#clear()">clear</a></strong>()</code>
<div class="block">Clear any nested diagnostic information if any.</div>
</td>
</tr>
<tr class="rowColor">
<td class="colFirst"><code>static <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Stack.html?is-external=true" title="class or interface in java.util">Stack</a></code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#cloneStack()">cloneStack</a></strong>()</code>
<div class="block">Clone the diagnostic context for the current thread.</div>
</td>
</tr>
<tr class="altColor">
<td class="colFirst"><code>static <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#get()">get</a></strong>()</code>
<div class="block"><strong style="color:#FF4040">Never use this method directly.</strong></div>
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<td class="colFirst"><code>static int</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#getDepth()">getDepth</a></strong>()</code>
<div class="block">Get the current nesting depth of this diagnostic context.</div>
</td>
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#inherit(java.util.Stack)">inherit</a></strong>(<a href="http://docs.oracle.com/javase/7/docs/api/java/util/Stack.html?is-external=true" title="class or interface in java.util">Stack</a>&lt;<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&gt;&nbsp;stack)</code>
<div class="block">Inherit the diagnostic context of another thread.</div>
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<tr class="rowColor">
<td class="colFirst"><code>static <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#peek()">peek</a></strong>()</code>
<div class="block">Looks at the last diagnostic context at the top of this NDC
without removing it.</div>
</td>
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<tr class="altColor">
<td class="colFirst"><code>static <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#pop()">pop</a></strong>()</code>
<div class="block">Clients should call this method before leaving a diagnostic
context.</div>
</td>
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#push(java.lang.String)">push</a></strong>(<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;message)</code>
<div class="block">Push new diagnostic context information for the current thread.</div>
</td>
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#remove()">remove</a></strong>()</code>
<div class="block">Remove the diagnostic context for this thread.</div>
</td>
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<td class="colFirst"><code>static void</code></td>
<td class="colLast"><code><strong><a href="../../../org/apache/log4j/NDC.html#setMaxDepth(int)">setMaxDepth</a></strong>(int&nbsp;maxDepth)</code>
<div class="block">Set maximum depth of this diagnostic context.</div>
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<h3>Methods inherited from class&nbsp;java.lang.<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></h3>
<code><a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#clone()" title="class or interface in java.lang">clone</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#equals(java.lang.Object)" title="class or interface in java.lang">equals</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#finalize()" title="class or interface in java.lang">finalize</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#getClass()" title="class or interface in java.lang">getClass</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#hashCode()" title="class or interface in java.lang">hashCode</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notify()" title="class or interface in java.lang">notify</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notifyAll()" title="class or interface in java.lang">notifyAll</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#toString()" title="class or interface in java.lang">toString</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait()" title="class or interface in java.lang">wait</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait(long)" title="class or interface in java.lang">wait</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait(long,%20int)" title="class or interface in java.lang">wait</a></code></li>
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<h4>clear</h4>
<pre>public static&nbsp;void&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.38">clear</a>()</pre>
<div class="block">Clear any nested diagnostic information if any. This method is
useful in cases where the same thread can be potentially used
over and over in different unrelated contexts.
<p>
This method is equivalent to calling the <a href="../../../org/apache/log4j/NDC.html#setMaxDepth(int)"><code>setMaxDepth(int)</code></a>
method with a zero <code>maxDepth</code> argument.
</p></div>
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<h4>cloneStack</h4>
<pre>public static&nbsp;<a href="http://docs.oracle.com/javase/7/docs/api/java/util/Stack.html?is-external=true" title="class or interface in java.util">Stack</a>&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.58">cloneStack</a>()</pre>
<div class="block">Clone the diagnostic context for the current thread.
<p>
Internally a diagnostic context is represented as a stack. A
given thread can supply the stack (i.e. diagnostic context) to a
child thread so that the child can inherit the parent thread's
diagnostic context.
</p>
<p>
The child thread uses the <a href="../../../org/apache/log4j/NDC.html#inherit(java.util.Stack)"><code>inherit</code></a> method to
inherit the parent's diagnostic context.
</p></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>Stack A clone of the current thread's diagnostic context.</dd></dl>
</li>
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<a name="inherit(java.util.Stack)">
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<h4>inherit</h4>
<pre>public static&nbsp;void&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.88">inherit</a>(<a href="http://docs.oracle.com/javase/7/docs/api/java/util/Stack.html?is-external=true" title="class or interface in java.util">Stack</a>&lt;<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&gt;&nbsp;stack)</pre>
<div class="block">Inherit the diagnostic context of another thread.
<p>
The parent thread can obtain a reference to its diagnostic
context using the <a href="../../../org/apache/log4j/NDC.html#cloneStack()"><code>cloneStack()</code></a> method. It should
communicate this information to its child so that it may inherit
the parent's diagnostic context.
</p>
<p>
The parent's diagnostic context is cloned before being
inherited. In other words, once inherited, the two diagnostic
contexts can be managed independently.
</p>
<p>
In java, a child thread cannot obtain a reference to its
parent, unless it is directly handed the reference. Consequently,
there is no client-transparent way of inheriting diagnostic
contexts. Do you know any solution to this problem?
</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>stack</code> - The diagnostic context of the parent thread.</dd></dl>
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<h4>get</h4>
<pre>public static&nbsp;<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.98">get</a>()</pre>
<div class="block"><strong style="color:#FF4040">Never use this method directly.</strong></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>The string value of the specified key.</dd></dl>
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<h4>getDepth</h4>
<pre>public static&nbsp;int&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.107">getDepth</a>()</pre>
<div class="block">Get the current nesting depth of this diagnostic context.</div>
<dl><dt><span class="strong">Returns:</span></dt><dd>int The number of elements in the call stack.</dd><dt><span class="strong">See Also:</span></dt><dd><a href="../../../org/apache/log4j/NDC.html#setMaxDepth(int)"><code>setMaxDepth(int)</code></a></dd></dl>
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<a name="pop()">
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<h4>pop</h4>
<pre>public static&nbsp;<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.120">pop</a>()</pre>
<div class="block">Clients should call this method before leaving a diagnostic
context.
<p>
The returned value is the value that was pushed last. If no
context is available, then the empty string "" is returned.
</p></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>String The innermost diagnostic context.</dd></dl>
</li>
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<a name="peek()">
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<h4>peek</h4>
<pre>public static&nbsp;<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.133">peek</a>()</pre>
<div class="block">Looks at the last diagnostic context at the top of this NDC
without removing it.
<p>
The returned value is the value that was pushed last. If no
context is available, then the empty string "" is returned.
</p></div>
<dl><dt><span class="strong">Returns:</span></dt><dd>String The innermost diagnostic context.</dd></dl>
</li>
</ul>
<a name="push(java.lang.String)">
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<h4>push</h4>
<pre>public static&nbsp;void&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.145">push</a>(<a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>&nbsp;message)</pre>
<div class="block">Push new diagnostic context information for the current thread.
<p>
The contents of the <code>message</code> parameter is
determined solely by the client.
</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>message</code> - The new diagnostic context information.</dd></dl>
</li>
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<h4>remove</h4>
<pre>public static&nbsp;void&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.169">remove</a>()</pre>
<div class="block">Remove the diagnostic context for this thread.
<p>
Each thread that created a diagnostic context by calling
<a href="../../../org/apache/log4j/NDC.html#push(java.lang.String)"><code>push(java.lang.String)</code></a> should call this method before exiting. Otherwise,
the memory used by the <b>thread</b> cannot be reclaimed by the
VM.
</p>
<p>
As this is such an important problem in heavy duty systems and
because it is difficult to always guarantee that the remove
method is called before exiting a thread, this method has been
augmented to lazily remove references to dead threads. In
practice, this means that you can be a little sloppy and
occasionally forget to call <code>remove</code> before exiting a
thread. However, you must call <code>remove</code> sometime. If
you never call it, then your application is sure to run out of
memory.
</p></div>
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<h4>setMaxDepth</h4>
<pre>public static&nbsp;void&nbsp;<a href="../../../src-html/org/apache/log4j/NDC.html#line.204">setMaxDepth</a>(int&nbsp;maxDepth)</pre>
<div class="block">Set maximum depth of this diagnostic context. If the current
depth is smaller or equal to <code>maxDepth</code>, then no
action is taken.
<p>
This method is a convenient alternative to multiple <a href="../../../org/apache/log4j/NDC.html#pop()"><code>pop()</code></a> calls. Moreover, it is often the case that at the end of
complex call sequences, the depth of the NDC is
unpredictable. The <code>setMaxDepth</code> method circumvents
this problem.
</p>
<p>
For example, the combination
</p>
<pre>
void foo() {
&nbsp; int depth = NDC.getDepth();
&nbsp; ... complex sequence of calls
&nbsp; NDC.setMaxDepth(depth);
}
</pre>
<p>
ensures that between the entry and exit of foo the depth of the
diagnostic stack is conserved.
</p></div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>maxDepth</code> - The maximum depth of the stack.</dd><dt><span class="strong">See Also:</span></dt><dd><a href="../../../org/apache/log4j/NDC.html#getDepth()"><code>getDepth()</code></a></dd></dl>
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