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 <h2 title="Interface Filter" class="title">Interface Filter</h2>
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 <pre>public interface <span class="typeNameLabel">Filter</span></pre>
 <div class="block"><p>
  A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static
  content), or on the response from a resource, or both.
  </p>

  <p>
  Filters perform filtering in the <code>doFilter</code> method. Every Filter has access to a FilterConfig object from
  which it can obtain its initialization parameters, and a reference to the ServletContext which it can use, for
  example, to load resources needed for filtering tasks.

  <p>
  Filters are configured in the deployment descriptor of a web application.

  <p>
  Examples that have been identified for this design are:
  <ol>
  <li>Authentication Filters
  <li>Logging and Auditing Filters
  <li>Image conversion Filters
  <li>Data compression Filters
  <li>Encryption Filters
  <li>Tokenizing Filters
  <li>Filters that trigger resource access events
  <li>XSL/T filters
  <li>Mime-type chain Filter
  </ol></div>
 <dl>
 <dt><span class="simpleTagLabel">Since:</span></dt>
 <dd>Servlet 2.3</dd>
 </dl>
 </li>
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 <td class="colFirst"><code>default void</code></td>
 <td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#destroy--">destroy</a></span>()</code>
 <div class="block">
  Called by the web container to indicate to a filter that it is being taken out of service.</div>
 </td>
 </tr>
 <tr id="i1" class="rowColor">
 <td class="colFirst"><code>void</code></td>
 <td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#doFilter-jakarta.servlet.ServletRequest-jakarta.servlet.ServletResponse-jakarta.servlet.FilterChain-">doFilter</a></span>(<a href="../../jakarta/servlet/ServletRequest.html" title="interface in jakarta.servlet">ServletRequest</a>&nbsp;request,
         <a href="../../jakarta/servlet/ServletResponse.html" title="interface in jakarta.servlet">ServletResponse</a>&nbsp;response,
         <a href="../../jakarta/servlet/FilterChain.html" title="interface in jakarta.servlet">FilterChain</a>&nbsp;chain)</code>
 <div class="block">The <code>doFilter</code> method of the Filter is called by the container each time a request/response pair is passed
  through the chain due to a client request for a resource at the end of the chain.</div>
 </td>
 </tr>
 <tr id="i2" class="altColor">
 <td class="colFirst"><code>default void</code></td>
 <td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#init-jakarta.servlet.FilterConfig-">init</a></span>(<a href="../../jakarta/servlet/FilterConfig.html" title="interface in jakarta.servlet">FilterConfig</a>&nbsp;filterConfig)</code>
 <div class="block">
  Called by the web container to indicate to a filter that it is being placed into service.</div>
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 <h4>init</h4>
 <pre>default&nbsp;void&nbsp;init(<a href="../../jakarta/servlet/FilterConfig.html" title="interface in jakarta.servlet">FilterConfig</a>&nbsp;filterConfig)
            throws <a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></pre>
 <div class="block"><p>
  Called by the web container to indicate to a filter that it is being placed into service.
  </p>

  <p>
  The servlet container calls the init method exactly once after instantiating the filter. The init method must
  complete successfully before the filter is asked to do any filtering work.
  </p>

  <p>
  The web container cannot place the filter into service if the init method either
  </p>
  <ol>
  <li>Throws a ServletException
  <li>Does not return within a time period defined by the web container
  </ol></div>
 <dl>
 <dt><span class="paramLabel">Parameters:</span></dt>
 <dd><code>filterConfig</code> - a <code>FilterConfig</code> object containing the filter's configuration and initialization
  parameters</dd>
 <dt><span class="throwsLabel">Throws:</span></dt>
 <dd><code><a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></code> - if an exception has occurred that interferes with the filter's normal operation</dd>
 </dl>
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 <h4>doFilter</h4>
 <pre>void&nbsp;doFilter(<a href="../../jakarta/servlet/ServletRequest.html" title="interface in jakarta.servlet">ServletRequest</a>&nbsp;request,
               <a href="../../jakarta/servlet/ServletResponse.html" title="interface in jakarta.servlet">ServletResponse</a>&nbsp;response,
               <a href="../../jakarta/servlet/FilterChain.html" title="interface in jakarta.servlet">FilterChain</a>&nbsp;chain)
        throws java.io.IOException,
               <a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></pre>
 <div class="block">The <code>doFilter</code> method of the Filter is called by the container each time a request/response pair is passed
  through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this
  method allows the Filter to pass on the request and response to the next entity in the chain.

  <p>
  A typical implementation of this method would follow the following pattern:
  <ol>
  <li>Examine the request
  <li>Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
  <li>Optionally wrap the response object with a custom implementation to filter content or headers for output
  filtering
  <li>
  <ul>
  <li><strong>Either</strong> invoke the next entity in the chain using the FilterChain object
  (<code>chain.doFilter()</code>),
  <li><strong>or</strong> not pass on the request/response pair to the next entity in the filter chain to block the
  request processing
  </ul>
  <li>Directly set headers on the response after invocation of the next entity in the filter chain.
  </ol></div>
 <dl>
 <dt><span class="paramLabel">Parameters:</span></dt>
 <dd><code>request</code> - the <code>ServletRequest</code> object contains the client's request</dd>
 <dd><code>response</code> - the <code>ServletResponse</code> object contains the filter's response</dd>
 <dd><code>chain</code> - the <code>FilterChain</code> for invoking the next filter or the resource</dd>
 <dt><span class="throwsLabel">Throws:</span></dt>
 <dd><code>java.io.IOException</code> - if an I/O related error has occurred during the processing</dd>
 <dd><code><a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></code> - if an exception occurs that interferes with the filter's normal operation</dd>
 <dt><span class="seeLabel">See Also:</span></dt>
 <dd><a href="../../jakarta/servlet/UnavailableException.html" title="class in jakarta.servlet"><code>UnavailableException</code></a></dd>
 </dl>
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 <h4>destroy</h4>
 <pre>default&nbsp;void&nbsp;destroy()</pre>
 <div class="block"><p>
  Called by the web container to indicate to a filter that it is being taken out of service.
  </p>

  <p>
  This method is only called once all threads within the filter's doFilter method have exited or after a timeout period
  has passed. After the web container calls this method, it will not call the doFilter method again on this instance of
  the filter.
  </p>

  <p>
  This method gives the filter an opportunity to clean up any resources that are being held (for example, memory, file
  handles, threads) and make sure that any persistent state is synchronized with the filter's current state in memory.
  </p></div>
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	<h2 title="Interface Filter" class="title">Interface Filter</h2>
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	<dd><a href="../../jakarta/servlet/GenericFilter.html" title="class in jakarta.servlet">GenericFilter</a>, <a href="../../jakarta/servlet/http/HttpFilter.html" title="class in jakarta.servlet.http">HttpFilter</a></dd>
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	<pre>public interface <span class="typeNameLabel">Filter</span></pre>
	<div class="block"><p>
	A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static
	content), or on the response from a resource, or both.
	</p>

	<p>
	Filters perform filtering in the <code>doFilter</code> method. Every Filter has access to a FilterConfig object from
	which it can obtain its initialization parameters, and a reference to the ServletContext which it can use, for
	example, to load resources needed for filtering tasks.

	<p>
	Filters are configured in the deployment descriptor of a web application.

	<p>
	Examples that have been identified for this design are:
	<ol>
	<li>Authentication Filters
	<li>Logging and Auditing Filters
	<li>Image conversion Filters
	<li>Data compression Filters
	<li>Encryption Filters
	<li>Tokenizing Filters
	<li>Filters that trigger resource access events
	<li>XSL/T filters
	<li>Mime-type chain Filter
	</ol></div>
	<dl>
	<dt><span class="simpleTagLabel">Since:</span></dt>
	<dd>Servlet 2.3</dd>
	</dl>
	</li>
	</ul>
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	<td class="colFirst"><code>default void</code></td>
	<td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#destroy--">destroy</a></span>()</code>
	<div class="block">
	Called by the web container to indicate to a filter that it is being taken out of service.</div>
	</td>
	</tr>
	<tr id="i1" class="rowColor">
	<td class="colFirst"><code>void</code></td>
	<td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#doFilter-jakarta.servlet.ServletRequest-jakarta.servlet.ServletResponse-jakarta.servlet.FilterChain-">doFilter</a></span>(<a href="../../jakarta/servlet/ServletRequest.html" title="interface in jakarta.servlet">ServletRequest</a> request,
	<a href="../../jakarta/servlet/ServletResponse.html" title="interface in jakarta.servlet">ServletResponse</a> response,
	<a href="../../jakarta/servlet/FilterChain.html" title="interface in jakarta.servlet">FilterChain</a> chain)</code>
	<div class="block">The <code>doFilter</code> method of the Filter is called by the container each time a request/response pair is passed
	through the chain due to a client request for a resource at the end of the chain.</div>
	</td>
	</tr>
	<tr id="i2" class="altColor">
	<td class="colFirst"><code>default void</code></td>
	<td class="colLast"><code><span class="memberNameLink"><a href="../../jakarta/servlet/Filter.html#init-jakarta.servlet.FilterConfig-">init</a></span>(<a href="../../jakarta/servlet/FilterConfig.html" title="interface in jakarta.servlet">FilterConfig</a> filterConfig)</code>
	<div class="block">
	Called by the web container to indicate to a filter that it is being placed into service.</div>
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	<h4>init</h4>
	<pre>default void init(<a href="../../jakarta/servlet/FilterConfig.html" title="interface in jakarta.servlet">FilterConfig</a> filterConfig)
	throws <a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></pre>
	<div class="block"><p>
	Called by the web container to indicate to a filter that it is being placed into service.
	</p>

	<p>
	The servlet container calls the init method exactly once after instantiating the filter. The init method must
	complete successfully before the filter is asked to do any filtering work.
	</p>

	<p>
	The web container cannot place the filter into service if the init method either
	</p>
	<ol>
	<li>Throws a ServletException
	<li>Does not return within a time period defined by the web container
	</ol></div>
	<dl>
	<dt><span class="paramLabel">Parameters:</span></dt>
	<dd><code>filterConfig</code> - a <code>FilterConfig</code> object containing the filter's configuration and initialization
	parameters</dd>
	<dt><span class="throwsLabel">Throws:</span></dt>
	<dd><code><a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></code> - if an exception has occurred that interferes with the filter's normal operation</dd>
	</dl>
	</li>
	</ul>
	<a name="doFilter-jakarta.servlet.ServletRequest-jakarta.servlet.ServletResponse-jakarta.servlet.FilterChain-">
	<!-- -->
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	<li class="blockList">
	<h4>doFilter</h4>
	<pre>void doFilter(<a href="../../jakarta/servlet/ServletRequest.html" title="interface in jakarta.servlet">ServletRequest</a> request,
	<a href="../../jakarta/servlet/ServletResponse.html" title="interface in jakarta.servlet">ServletResponse</a> response,
	<a href="../../jakarta/servlet/FilterChain.html" title="interface in jakarta.servlet">FilterChain</a> chain)
	throws java.io.IOException,
	<a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></pre>
	<div class="block">The <code>doFilter</code> method of the Filter is called by the container each time a request/response pair is passed
	through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this
	method allows the Filter to pass on the request and response to the next entity in the chain.

	<p>
	A typical implementation of this method would follow the following pattern:
	<ol>
	<li>Examine the request
	<li>Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
	<li>Optionally wrap the response object with a custom implementation to filter content or headers for output
	filtering
	<li>
	<ul>
	<li><strong>Either</strong> invoke the next entity in the chain using the FilterChain object
	(<code>chain.doFilter()</code>),
	<li><strong>or</strong> not pass on the request/response pair to the next entity in the filter chain to block the
	request processing
	</ul>
	<li>Directly set headers on the response after invocation of the next entity in the filter chain.
	</ol></div>
	<dl>
	<dt><span class="paramLabel">Parameters:</span></dt>
	<dd><code>request</code> - the <code>ServletRequest</code> object contains the client's request</dd>
	<dd><code>response</code> - the <code>ServletResponse</code> object contains the filter's response</dd>
	<dd><code>chain</code> - the <code>FilterChain</code> for invoking the next filter or the resource</dd>
	<dt><span class="throwsLabel">Throws:</span></dt>
	<dd><code>java.io.IOException</code> - if an I/O related error has occurred during the processing</dd>
	<dd><code><a href="../../jakarta/servlet/ServletException.html" title="class in jakarta.servlet">ServletException</a></code> - if an exception occurs that interferes with the filter's normal operation</dd>
	<dt><span class="seeLabel">See Also:</span></dt>
	<dd><a href="../../jakarta/servlet/UnavailableException.html" title="class in jakarta.servlet"><code>UnavailableException</code></a></dd>
	</dl>
	</li>
	</ul>
	<a name="destroy--">
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	<h4>destroy</h4>
	<pre>default void destroy()</pre>
	<div class="block"><p>
	Called by the web container to indicate to a filter that it is being taken out of service.
	</p>

	<p>
	This method is only called once all threads within the filter's doFilter method have exited or after a timeout period
	has passed. After the web container calls this method, it will not call the doFilter method again on this instance of
	the filter.
	</p>

	<p>
	This method gives the filter an opportunity to clean up any resources that are being held (for example, memory, file
	handles, threads) and make sure that any persistent state is synchronized with the filter's current state in memory.
	</p></div>
	</li>
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