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webapps/docs/config/engine.xml
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268
webapps/docs/config/engine.xml
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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<!DOCTYPE document [
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<!ENTITY project SYSTEM "project.xml">
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]>
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<document url="engine.html">
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&project;
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<properties>
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<author email="craigmcc@apache.org">Craig R. McClanahan</author>
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<title>The Engine Container</title>
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</properties>
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<body>
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<section name="Table of Contents">
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<toc/>
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</section>
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<section name="Introduction">
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<p>The <strong>Engine</strong> element represents the entire request
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processing machinery associated with a particular Catalina
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<a href="service.html">Service</a>. It receives and processes
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<em>all</em> requests from one or more <strong>Connectors</strong>,
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and returns the completed response to the Connector for ultimate
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transmission back to the client.</p>
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<p>Exactly one <strong>Engine</strong> element MUST be nested inside
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a <a href="service.html">Service</a> element, following all of the
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corresponding Connector elements associated with this Service.</p>
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</section>
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<section name="Attributes">
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<subsection name="Common Attributes">
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<p>All implementations of <strong>Engine</strong>
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support the following attributes:</p>
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<attributes>
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<attribute name="backgroundProcessorDelay" required="false">
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<p>This value represents the delay in seconds between the
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invocation of the backgroundProcess method on this engine and
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its child containers, including all hosts and contexts.
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Child containers will not be invoked if their delay value is not
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negative (which would mean they are using their own processing
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thread). Setting this to a positive value will cause
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a thread to be spawn. After waiting the specified amount of time,
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the thread will invoke the backgroundProcess method on this engine
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and all its child containers. If not specified, the default value for
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this attribute is 10, which represent a 10 seconds delay.</p>
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</attribute>
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<attribute name="className" required="false">
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<p>Java class name of the implementation to use. This class must
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implement the <code>org.apache.catalina.Engine</code> interface.
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If not specified, the standard value (defined below) will be used.</p>
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</attribute>
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<attribute name="defaultHost" required="true">
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<p>The default host name, which identifies the
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<a href="host.html">Host</a> that will process requests directed
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to host names on this server, but which are not configured in
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this configuration file. This name MUST match the <code>name</code>
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attributes of one of the <a href="host.html">Host</a> elements
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nested immediately inside.</p>
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</attribute>
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<attribute name="jvmRoute" required="false">
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<p>Identifier which must be used in load balancing scenarios to enable
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session affinity. The identifier, which must be unique across all
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Tomcat servers which participate in the cluster, will be appended to
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the generated session identifier, therefore allowing the front end
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proxy to always forward a particular session to the same Tomcat
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instance.</p>
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<p>
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Note that the <code>jvmRoute</code> can also be set using the
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<code>jvmRoute</code> system property. The <code>jvmRoute</code>
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set in an <code><Engine></code> attribute will override
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any <code>jvmRoute</code> system property.
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</p>
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</attribute>
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<attribute name="name" required="true">
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<p>Logical name of this Engine, used in log and error messages. <em>When
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using multiple <a href="service.html">Service</a> elements in the same
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<a href="server.html">Server</a>, each Engine MUST be assigned a unique
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name.</em></p>
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</attribute>
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<attribute name="startStopThreads" required="false">
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<p>The number of threads this <strong>Engine</strong> will use to start
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child <a href="host.html">Host</a> elements in parallel. The special
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value of 0 will result in the value of
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<code>Runtime.getRuntime().availableProcessors()</code> being used.
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Negative values will result in
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<code>Runtime.getRuntime().availableProcessors() + value</code> being
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used unless this is less than 1 in which case 1 thread will be used. If
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not specified, the default value of 1 will be used. </p>
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</attribute>
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</attributes>
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</subsection>
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<subsection name="Standard Implementation">
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<p>The standard implementation of <strong>Engine</strong> is
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<strong>org.apache.catalina.core.StandardEngine</strong>.
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It supports the following additional attributes (in addition to the
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common attributes listed above):</p>
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<attributes>
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</attributes>
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</subsection>
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</section>
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<section name="Nested Components">
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<p>You can nest one or more <a href="host.html">Host</a> elements inside
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this <strong>Engine</strong> element, each representing a different virtual
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host associated with this server. At least one <a href="host.html">Host</a>
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is required, and one of the nested <a href="host.html">Hosts</a> MUST
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have a name that matches the name specified for the
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<code>defaultHost</code> attribute, listed above.</p>
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<p>You can nest at most one instance of the following utility components
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by nesting a corresponding element inside your <strong>Engine</strong>
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element:</p>
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<ul>
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<li><a href="realm.html"><strong>Realm</strong></a> -
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Configure a realm that will allow its
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database of users, and their associated roles, to be shared across all
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<a href="host.html">Hosts</a> and <a href="context.html">Contexts</a>
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nested inside this Engine, unless overridden by a
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<a href="realm.html">Realm</a> configuration at a lower level.</li>
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</ul>
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</section>
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<section name="Special Features">
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<subsection name="Logging">
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<p>An engine is associated with the
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<code>org.apache.catalina.core.ContainerBase.[enginename]</code>
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log category. Note that the brackets are actually part of the name,
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don't omit them.</p>
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</subsection>
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<subsection name="Access Logs">
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<p>When you run a web server, one of the output files normally generated
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is an <em>access log</em>, which generates one line of information for
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each request processed by the server, in a standard format. Catalina
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includes an optional <a href="valve.html">Valve</a> implementation that
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can create access logs in the same standard format created by web servers,
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or in any number of custom formats.</p>
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<p>You can ask Catalina to create an access log for all requests
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processed by an <a href="engine.html">Engine</a>,
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<a href="host.html">Host</a>, or <a href="context.html">Context</a>
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by nesting a <a href="valve.html">Valve</a> element like this:</p>
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<source><![CDATA[<Engine name="Standalone" ...>
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...
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<Valve className="org.apache.catalina.valves.AccessLogValve"
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prefix="catalina_access_log" suffix=".txt"
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pattern="common"/>
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...
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</Engine>]]></source>
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<p>See <a href="valve.html#Access_Logging">Access Logging Valves</a>
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for more information on the configuration attributes that are
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supported.</p>
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</subsection>
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<subsection name="Lifecycle Listeners">
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<p>If you have implemented a Java object that needs to know when this
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<strong>Engine</strong> is started or stopped, you can declare it by
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nesting a <strong>Listener</strong> element inside this element. The
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class name you specify must implement the
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<code>org.apache.catalina.LifecycleListener</code> interface, and
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it will be notified about the occurrence of the corresponding
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lifecycle events. Configuration of such a listener looks like this:</p>
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<source><![CDATA[<Engine name="Standalone" ...>
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...
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<Listener className="com.mycompany.mypackage.MyListener" ... >
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...
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</Engine>]]></source>
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<p>Note that a Listener can have any number of additional properties
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that may be configured from this element. Attribute names are matched
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to corresponding JavaBean property names using the standard property
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method naming patterns.</p>
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</subsection>
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<subsection name="Request Filters">
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<p>You can ask Catalina to check the IP address, or host name, on every
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incoming request directed to the surrounding
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<a href="engine.html">Engine</a>, <a href="host.html">Host</a>, or
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<a href="context.html">Context</a> element. The remote address or name
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will be checked against configured "accept" and/or "deny"
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filters, which are defined using <code>java.util.regex</code> Regular
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Expression syntax. Requests that come from locations that are
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not accepted will be rejected with an HTTP "Forbidden" error.
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Example filter declarations:</p>
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<source><![CDATA[<Engine name="Standalone" ...>
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...
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<Valve className="org.apache.catalina.valves.RemoteHostValve"
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allow=".*\.mycompany\.com|www\.yourcompany\.com"/>
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<Valve className="org.apache.catalina.valves.RemoteAddrValve"
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deny="192\.168\.1\.\d+"/>
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...
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</Engine>]]></source>
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<p>See <a href="valve.html#Remote_Address_Filter">Remote Address Filter</a>
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and <a href="valve.html#Remote_Host_Filter">Remote Host Filter</a> for
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more information about the configuration options that are supported.</p>
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</subsection>
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</section>
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</body>
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</document>
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