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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="context.html">

  &project;

  <properties>
    <author email="craigmcc@apache.org">Craig R. McClanahan</author>
    <title>The Context Container</title>
  </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

<section name="Introduction">

    <blockquote><em>
    <p>The description below uses the variable name $CATALINA_BASE to refer the
    base directory against which most relative paths are resolved. If you have
    not configured Tomcat 6 for multiple instances by setting a CATALINA_BASE
    directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME,
    the directory into which you have installed Tomcat 6.</p>
    </em></blockquote>

  <p>The <strong>Context</strong> element represents a <em>web
  application</em>, which is run within a particular virtual host.
  Each web application is based on a <em>Web Application Archive</em>
  (WAR) file, or a corresponding directory containing the corresponding
  unpacked contents, as described in the Servlet Specification (version
  2.2 or later).  For more information about web application archives,
  you can download the
  <a href="http://wiki.apache.org/tomcat/Specifications">Servlet
  Specification</a>, and review the Tomcat
  <a href="../appdev/index.html">Application Developer's Guide</a>.</p>

  <p>The web application used to process each HTTP request is selected
  by Catalina based on matching the longest possible prefix of the
  Request URI against the <em>context path</em> of each defined Context.
  Once selected, that Context will select an appropriate servlet to
  process the incoming request, according to the servlet mappings defined
  in the <em>web application deployment descriptor</em> file (which MUST
  be located at <code>/WEB-INF/web.xml</code> within the web app's
  directory hierarchy).</p>

  <p>You may define as many <strong>Context</strong> elements as you
  wish.  Each such Context MUST have a unique context path within a virtual
  host. In
  addition, a Context must be present with a context path equal to
  a zero-length string.  This Context becomes the <em>default</em>
  web application for this virtual host, and is used to process all
  requests that do not match any other Context's context path.</p>

  <subsection name="Naming">
  <p>When <code>autoDeploy</code> or <code>deployOnStartup</code> operations
  are performed by a Host, the web application is specified by a context XML
  file in <a href="host.html">Host</a>&apos;s <code>xmlBase</code>
  directory or by a WAR file or a directory file in Host&apos;s
  <code>appBase</code> directory.
  In this case the context path is derived from the name of the file that
  is being deployed. Consequently, the context path <strong>may not</strong>
  be defined in a <code>META-INF/context.xml</code> embedded in
  the application. There is, therefore, a close relationship between the
  <em>context path</em> and
  the <em>base file name</em> (the name minus <code>.war</code> or
  <code>.xml</code> extension) of the file.</p>

  <p>Let us assume that you want to deploy your application to respond to
  requests to URIs starting with certain context path. According to the
  Servlet specification, the context path may be an empty string, or a
  string starting with '/'. The rules to define the names for this context
  path are the following:</p>

  <ul>
    <li>If the context path is a zero length string, the <em>base name</em> is
    <code>"ROOT"</code> (uppercase)</li>
    <li>If the context path is not a zero length string, the <em>base
    name</em> is the context path with the leading '/' removed and any
    remaining '/' characters in the path replaced with '#'.</li>
  </ul>

  <p>To help clarify these rules, some examples are given in the following
  table.</p>

  <table class="detail-table">
    <tr>
      <th>Context Path</th>
      <th>Base File Name</th>
    </tr>
    <tr><td>/foo</td><td>foo</td></tr>
    <tr>
      <td>/foo/bar</td><td>foo#bar</td>
    </tr>
    <tr>
      <td><i>Empty String</i></td>
      <td>ROOT</td>
    </tr>
  </table>

  <p>If you want to deploy a WAR file or a directory using a context path that
  is not related to the base file name then one of the following options must
  be used to prevent double-deployment:
  </p>
  <ul>
  <li>Disable autoDeploy and deployOnStartup and define all
  <strong>Context</strong>s in server.xml</li>
  <li>Locate the WAR and/or directory outside of the Host&apos;s appBase and use
      a context.xml file with a docBase attribute to define it.</li>
  </ul>
  </subsection>

  <subsection name="Defining a context">
  <p><b>It is NOT recommended to place
  &lt;Context&gt; elements directly in the server.xml file.</b> This
  is because it makes modifying the <strong>Context</strong> configuration
  more invasive since the main <code>conf/server.xml</code> file cannot be
  reloaded without restarting Tomcat.</p>

  <p>Individual <strong>Context</strong> elements may be explicitly defined:
  </p>
  <ul>
  <li>In an individual file at <code>/META-INF/context.xml</code> inside the
  application files. In Tomcat 6 this file is automatically copied to
  <code>$CATALINA_BASE/conf/[enginename]/[hostname]/</code> and renamed to
  application&apos;s base file name plus a ".xml" extension.
  (This automated copying became optional in Tomcat 7).
  </li>
  <li>In individual files (with a ".xml" extension) in the
  <code>$CATALINA_BASE/conf/[enginename]/[hostname]/</code> directory.
  The context path will be derived from the base name of the file
  (the file name less the .xml extension). This file will always take precedence
  over any context.xml file packaged in the web application&apos;s META-INF
  directory.</li>
  <li>Inside a <a href="host.html">Host</a> element in the main
  <code>conf/server.xml</code>.</li>
  </ul>

  <p>Default <strong>Context</strong> elements may be defined that apply to
  multiple web applications. Configuration for an individual web application
  will override anything configured in one of these defaults. Any nested
  elements, e.g. &lt;Resource&gt; elements, that are defined in a default
  <strong>Context</strong> will be created once for each
  <strong>Context</strong> to which the default applies. They will <b>not</b> be
  shared between <strong>Context</strong> elements.
  </p>
  <ul>
  <li>In the <code>$CATALINA_BASE/conf/context.xml</code> file:
  the Context element information will be loaded by all web applications.</li>
  <li>In the
  <code>$CATALINA_BASE/conf/[enginename]/[hostname]/context.xml.default</code>
  file: the Context element information will be loaded by all web applications
  of that host.</li>
  </ul>

  <p>With the exception of server.xml, files that define <strong>Context
  </strong> elements may only define a single <strong>Context</strong> element.
  </p>

  <p>In addition to explicitly specified Context elements, there are
  several techniques by which Context elements can be created automatically
  for you.  See <a href="host.html#Automatic_Application_Deployment">
  Automatic Application Deployment</a> and
  <a href="host.html#User_Web_Applications">User Web Applications</a>
  for more information.</p>

  <p>To define multiple contexts that use a single WAR file or directory,
  use one of the options described in the <a href="#Naming">Naming</a>
  section above for creating a <strong>Context</strong> that has a path
  that is not related to the base file name.</p>
  </subsection>

</section>


<section name="Attributes">

  <subsection name="Common Attributes">

    <p>All implementations of <strong>Context</strong>
    support the following attributes:</p>

    <attributes>

      <attribute name="backgroundProcessorDelay" required="false">
        <p>This value represents the delay in seconds between the 
        invocation of the backgroundProcess method on this context and 
        its child containers, including all wrappers. 
        Child containers will not be invoked if their delay value is not 
        negative (which would mean they are using their own processing 
        thread). Setting this to a positive value will cause 
        a thread to be spawn. After waiting the specified amount of time, 
        the thread will invoke the backgroundProcess method on this host 
        and all its child containers. A context will use background 
        processing to perform session expiration and class monitoring for
        reloading. If not specified, the default value for this attribute is 
        -1, which means the context will rely on the background processing 
        thread of its parent host.</p>
      </attribute>

      <attribute name="className" required="false">
        <p>Java class name of the implementation to use.  This class must
        implement the <code>org.apache.catalina.Context</code> interface.
        If not specified, the standard value (defined below) will be used.</p>
      </attribute>

      <attribute name="cookies" required="false">
        <p>Set to <code>true</code> if you want cookies to be used for
        session identifier communication if supported by the client (this
        is the default).  Set to <code>false</code> if you want to disable
        the use of cookies for session identifier communication, and rely
        only on URL rewriting by the application.</p>
      </attribute>

      <attribute name="crossContext" required="false">
        <p>Set to <code>true</code> if you want calls within this application
        to <code>ServletContext.getContext()</code> to successfully return a
        request dispatcher for other web applications running on this virtual
        host.  Set to <code>false</code> (the default) in security
        conscious environments, to make <code>getContext()</code> always
        return <code>null</code>.</p>
      </attribute>

      <attribute name="disableURLRewriting" required="false">
        <p>Set to <code>true</code> to disable support for using URL rewriting
        to track session IDs for clients of this Context. URL rewriting is an
        optional component of the servlet 2.5 specification but disabling URL
        rewriting will result in non-compliant behaviour since the specification
        requires that there <em>must</em> be a way to retain sessions if the
        client doesn't allow session cookies. If not specified, the
        specification compliant default value of <code>false</code> will be
        used.</p>
      </attribute>

      <attribute name="docBase" required="true">
        <p>The <em>Document Base</em> (also known as the <em>Context
        Root</em>) directory for this web application, or the pathname
        to the web application archive file (if this web application is
        being executed directly from the WAR file). You may specify
        an absolute pathname for this directory or WAR file, or a pathname
        that is relative to the <code>appBase</code> directory of the
        owning <a href="host.html">Host</a>.</p>
        <p>The value of this field must not be set unless the Context element is
        defined in server.xml or the <code>docBase</code> is not located under
        the <a href="host.html">Host</a>&apos;s <code>appBase</code>.</p>
        <p>If a symbolic link is used for docBase then changes to the
        symbolic link will only be effective after a Tomcat restart or
        by undeploying and redeploying the context. A context reload is not
        sufficient.</p>
      </attribute>

      <attribute name="override" required="false">
        <p>Set to <code>true</code> to have explicit settings in this
        Context element override any corresponding settings in either the global
        or <a href="host.html">Host</a> default contexts.  By default, settings
        from a default context will be used.</p>
      </attribute>

      <attribute name="privileged" required="false">
        <p>Set to <code>true</code> to allow this context to use container
        servlets, like the manager servlet. Use of the <code>privileged</code>
        attribute will change the context's parent class loader to be the
        <em>Server</em> class loader rather than the <em>Shared</em> class
        loader. Note that in a default installation, the <em>Common</em> class
        loader is used for both the <em>Server</em> and the <em>Shared</em>
        class loaders.</p>
      </attribute>

      <attribute name="path" required="false">
        <p>The <em>context path</em> of this web application, which is
        matched against the beginning of each request URI to select the
        appropriate web application for processing.  All of the context paths
        within a particular <a href="host.html">Host</a> must be unique.
        If you specify a context path of an empty string (""), you are
        defining the <em>default</em> web application for this Host, which
        will process all requests not assigned to other Contexts.</p>
        <p>This attribute must only be used when statically defining a Context
        in server.xml. In all other circumstances, the path will be inferred
        from the filenames used for either the .xml context file or the docBase.
        </p>
        <p>Even when statically defining a Context in server.xml, this attribute
        must not be set unless either the docBase is not located under the
        <a href="host.html">Host</a>&apos;s <code>appBase</code> or both
        <code>deployOnStartup</code> and <code>autoDeploy</code> are false. If
        this rule is not followed, double deployment is likely to result.</p>
      </attribute>

      <attribute name="reloadable" required="false">
        <p>Set to <code>true</code> if you want Catalina to monitor classes in
        <code>/WEB-INF/classes/</code> and <code>/WEB-INF/lib</code> for
        changes, and automatically reload the web application if a change
        is detected.  This feature is very useful during application
        development, but it requires significant runtime overhead and is
        not recommended for use on deployed production applications.  That's
        why the default setting for this attribute is <i>false</i>.  You
        can use the <a href="../manager-howto.html">Manager</a> web
        application, however, to trigger reloads of deployed applications
        on demand.</p>
      </attribute>

      <attribute name="sessionCookieDomain" required="false">
        <p>The domain to be used for all session cookies created for this
        Context. If not set, no domain will be specified for session cookies.
        </p>
      </attribute>
      
      <attribute name="sessionCookieName" required="false">
        <p>The name to be used for all session cookies created for this
        Context. If not set, the default of JSESSIONID will be used. Note that
        this default will be overridden by the
        <strong>org.apache.catalina.SESSION_COOKIE_NAME</strong> system
        property.</p>
      </attribute>

      <attribute name="sessionCookiePath" required="false">
        <p>The path to be used for all session cookies created for this
        Context. If not set, the context path will be used. Note that this will
        be overridden by the <strong>emptySessionPath</strong> attribute on the
        connector used to access this Context.</p>
      </attribute>
      
      <attribute name="tldValidation" required="false">
        <p>If the value of this flag is <code>true</code>, the TLD files
        will be XML validated on context startup.  If the
        <code>org.apache.catalina.STRICT_SERVLET_COMPLIANCE</code>
        <a href="systemprops.html">system property</a> is set to
        <code>true</code>, the default value of this attribute will be
        <code>true</code>, else the default value will be <code>false</code>.
        Setting this attribute to <code>true</code> will incur a performance
        penalty.</p>
      </attribute>

      <attribute name="useHttpOnly" required="false">
       <p>Should the HttpOnly flag be set on session cookies to prevent client
          side script from accessing the session ID? Defaults to
          <code>false</code>.</p>
      </attribute>

      <attribute name="wrapperClass" required="false">
        <p>Java class name of the <code>org.apache.catalina.Wrapper</code>
        implementation class that will be used for servlets managed by this
        Context.  If not specified, a standard default value will be used.</p>
      </attribute>
      
      <attribute name="xmlBlockExternal" required="false">
        <p>If the value of this flag is <code>true</code>, the parsing of
        <code>web.xml</code>, <code>web-fragment.xml</code>, <code>*.tld</code>,
        <code>*.jspx</code>, <code>*.tagx</code> and <code>tagPlugins.xml</code>
        files for this web application will not permit external entities to be
        loaded. If a <code>SecurityManager</code> is configured then the default
        value of this attribute will be <code>true</code>, else the default
        value will be <code>false</code>.</p>
      </attribute>

      <attribute name="xmlNamespaceAware" required="false">
        <p>If the value of this flag is <code>true</code>, the parsing of the
        <code>web.xml</code> file for this web application will be
        namespace-aware. Note that <code>*.tld</code>, <code>*.jspx</code> and
        <code>*.tagx</code> files are always parsed using a namespace-aware
        parser and that the <code>tagPlugins.xml</code> file (if any) is never
        parsed using a namespace-aware parser. Note also that if you turn this
        flag on, you should probably also turn <code>xmlValidation</code> on. If
        the <code>org.apache.catalina.STRICT_SERVLET_COMPLIANCE</code>
        <a href="systemprops.html">system property</a> is set to
        <code>true</code>, the default value of this attribute will be
        <code>true</code>, else the default value will be <code>false</code>.
        Setting this attribute to <code>true</code> will incur a performance
        penalty.</p>
      </attribute>

      <attribute name="xmlValidation" required="false">
        <p>If the value of this flag is <code>true</code>, the parsing of the
        <code>web.xml</code> file for this web application will use a validating
        parser. If the
        <code>org.apache.catalina.STRICT_SERVLET_COMPLIANCE</code>
        <a href="systemprops.html">system property</a> is set to
        <code>true</code>, the default value of this attribute will be
        <code>true</code>, else the default value will be <code>false</code>.
        Setting this attribute to <code>true</code> will incur a performance
        penalty.</p>
      </attribute>


    </attributes>

  </subsection>


  <subsection name="Standard Implementation">

    <p>The standard implementation of <strong>Context</strong> is
    <strong>org.apache.catalina.core.StandardContext</strong>.
    It supports the following additional attributes (in addition to the
    common attributes listed above):</p>

    <attributes>

      <attribute name="allowLinking" required="false">
        <p>If the value of this flag is <code>true</code>, symlinks will be
        allowed inside the web application, pointing to resources outside the
        web application base path. If not specified, the default value
        of the flag is <code>false</code>.</p>
        <p><b>NOTE: This flag MUST NOT be set to true on the Windows platform
        (or any other OS which does not have a case sensitive filesystem),
        as it will disable case sensitivity checks, allowing JSP source code
        disclosure, among other security problems.</b></p>
      </attribute>

      <attribute name="antiJARLocking" required="false">
        <p>If true, the Tomcat classloader will take extra measures to avoid
        JAR file locking when resources are accessed inside JARs through URLs.
        This will impact startup time of applications, but could prove to be
        useful on platforms or configurations where file locking can occur.
        If not specified, the default value is <code>false</code>.</p>

        <p><code>antiJARLocking</code> is a subset of
        <code>antiResourceLocking</code> and therefore, to prevent duplicate
        work and possible issues, only one of these attributes should be set
        to <code>true</code> at any one time.</p>
      </attribute>

      <attribute name="antiResourceLocking" required="false">
        <p>If true, Tomcat will prevent any file locking.
        This will significantly impact startup time of applications, 
        but allows full webapp hot deploy and undeploy on platforms 
        or configurations where file locking can occur.
        If not specified, the default value is <code>false</code>.</p>
   
        <p><code>antiJARLocking</code> is a subset of
        <code>antiResourceLocking</code> and therefore, to prevent duplicate
        work and possible issues, only one of these attributes should be set
        to <code>true</code> at any one time.</p>

        <p>Please note that setting this to <code>true</code> has some side
        effects, including the disabling of JSP reloading in a running server:
        see <a href="http://issues.apache.org/bugzilla/show_bug.cgi?id=37668">
        Bugzilla 37668</a>.</p>

        <p>Please note that setting this flag to true in applications that are
        outside the appBase for the Host (the <code>webapps</code> directory
        by default) will cause the application to be <strong>deleted</strong> on
        Tomcat shutdown.  You probably don't want to do this, so think twice 
        before setting antiResourceLocking=true on a webapp that's outside the
        appBase for its Host.</p>
      </attribute>

      <attribute name="cacheMaxSize" required="false">
        <p>Maximum size of the static resource cache in kilobytes. 
        If not specified, the default value is <code>10240</code>
        (10 megabytes).</p>
      </attribute>

      <attribute name="cacheObjectMaxSize" required="false">
        <p>Maximum size of the static resource that will be placed in the cache.
        If not specified, the default value is <code>512</code>
        (512 kilobytes). If this value is greater than
        <code>cacheMaxSize/20</code> it will be reduced to
        <code>cacheMaxSize/20</code>.</p>
      </attribute>

      <attribute name="cacheTTL" required="false">
        <p>Amount of time in milliseconds between cache entries revalidation.
        If not specified, the default value is <code>5000</code> 
        (5 seconds).</p>
      </attribute>

      <attribute name="cachingAllowed" required="false">
        <p>If the value of this flag is <code>true</code>, the cache for static
        resources will be used. If not specified, the default value
        of the flag is <code>true</code>.</p>
      </attribute>

      <attribute name="caseSensitive" required="false">
        <p><strong>Deprecated.</strong> This option is removed in Tomcat 7
        onwards where the default of <code>true</code> is always used.</p>
        <p>If the value of this flag is <code>false</code>, all case sensitivity
        checks will be disabled. If not 
        specified, the default value of the flag is <code>true</code>.</p>
        <p><b>NOTE: This flag MUST NOT be set to false on the Windows platform
        (or any other OS which does not have a case sensitive filesystem),
        as it will disable case sensitivity checks, allowing JSP source code
        disclosure, among other security problems.</b></p>
      </attribute>

      <attribute name="clearReferencesHttpClientKeepAliveThread" required = "false">
        <p>If <code>true</code> and an <code>sun.net.www.http.HttpClient</code>
        keep-alive timer thread has been started by this web application and is
        still running, Tomcat will change the context class loader for that
        thread from the current <code>WebappClassLoader</code> to
        <code>WebappClassLoader#parent</code> to prevent a memory leak. Note
        that the keep-alive timer thread will stop on its own once the
        keep-alives all expire however, on a busy system that might not happen
        for some time. If not specified, the default value of
        <code>true</code> will be used.</p>
      </attribute>

      <attribute name="clearReferencesStopThreads" required = "false">
        <p>If <code>true</code>, Tomcat attempts to terminate threads that have
        been started by the web application. Stopping threads is performed via
        the deprecated (for good reason) <code>Thread.stop()</code> method and
        is likely to result in instability. As such, enabling this should be
        viewed as an option of last resort in a development environment and is
        not recommended in a production environment. If not specified, the
        default value of <code>false</code> will be used.</p>
      </attribute>

      <attribute name="clearReferencesStopTimerThreads" required = "false">
        <p>If <code>true</code>, Tomcat attempts to terminate
        <code>java.util.Timer</code> threads that have been started by the web
        application. Unlike standard threads, timer threads can be stopped
        safely although there may still be side-effects for the application. If
        not specified, the default value of <code>false</code> will be used.</p>
      </attribute>

      <attribute name="clearReferencesThreadLocals" required="false">
        <p>If <code>true</code>, Tomcat attempts to clear any ThreadLocal
        objects that are instances of classes loaded by this class loader.
        Failure to remove any such objects will result in a memory leak on web
        application stop, undeploy or reload.  If not specified, the default
        value of <code>false</code> will be used since the clearing of the
        ThreadLocal objects is not performed in a thread-safe manner.</p>
      </attribute>

      <attribute name="processTlds" required="false">
        <p>Whether the context should process TLDs on startup.  The default
        is true.  The false setting is intended for special cases
        that know in advance TLDs are not part of the webapp.</p>
      </attribute>

      <attribute name="swallowOutput" required="false">
        <p>If the value of this flag is <code>true</code>, the bytes output to
        System.out and System.err by the web application will be redirected to
        the web application logger. If not specified, the default value
        of the flag is <code>false</code>.</p>
      </attribute>

      <attribute name="unloadDelay" required="false">
        <p>Number of ms that the container will wait for servlets to unload.
        If not specified, the default value is <code>2000</code> ms.</p>
      </attribute>

      <attribute name="unpackWAR" required="false">
        <p>If true, Tomcat will unpack all compressed web applications before
        running them.
        If not specified, the default value is <code>true</code>.</p>
      </attribute>

      <attribute name="useNaming" required="false">
        <p>Set to <code>true</code> (the default) to have Catalina enable a
        JNDI <code>InitialContext</code> for this web application that is
        compatible with Java2 Enterprise Edition (J2EE) platform
        conventions.</p>
      </attribute>

      <attribute name="workDir" required="false">
        <p>Pathname to a scratch directory to be provided by this Context
        for temporary read-write use by servlets within the associated web
        application.  This directory will be made visible to servlets in the
        web application by a servlet context attribute (of type
        <code>java.io.File</code>) named
        <code>javax.servlet.context.tempdir</code> as described in the
        Servlet Specification.  If not specified, a suitable directory
        underneath <code>$CATALINA_BASE/work</code> will be provided.</p>
      </attribute>

    </attributes>

  </subsection>


</section>


<section name="Nested Components">

  <p>You can nest at most one instance of the following utility components
  by nesting a corresponding element inside your <strong>Context</strong>
  element:</p>
  <ul>
  <li><a href="loader.html"><strong>Loader</strong></a> -
      Configure the web application class loader that will be used to load
      servlet and bean classes for this web application.  Normally, the
      default configuration of the class loader will be sufficient.</li>
  <li><a href="manager.html"><strong>Manager</strong></a> -
      Configure the session manager that will be used to create, destroy,
      and persist HTTP sessions for this web application.  Normally, the
      default configuration of the session manager will be sufficient.</li>
  <li><a href="realm.html"><strong>Realm</strong></a> -
      Configure a realm that will allow its
      database of users, and their associated roles, to be utilized solely
      for this particular web application.  If not specified, this web
      application will utilize the Realm associated with the owning
      <a href="host.html">Host</a> or <a href="engine.html">Engine</a>.</li>
  <li><a href="resources.html"><strong>Resources</strong></a> -
      Configure the resource manager that will be used to access the static
      resources associated with this web application.  Normally, the
      default configuration of the resource manager will be sufficient.</li>
  <li><strong>WatchedResource</strong> - The auto deployer will monitor the 
      specified static resource of the web application for updates, and will
      reload the web application if is is updated. The content of this element
      must be a string.</li>
  </ul>

</section>


<section name="Special Features">


  <subsection name="Logging">

    <p>A context is associated with the 
       <code>org.apache.catalina.core.ContainerBase.[enginename].[hostname].[path]</code>
       log category.  Note that the brackets are actually part of the name, don't omit them.</p>

  </subsection>


  <subsection name="Access Logs">

    <p>When you run a web server, one of the output files normally generated
    is an <em>access log</em>, which generates one line of information for
    each request processed by the server, in a standard format.  Catalina
    includes an optional <a href="valve.html">Valve</a> implementation that
    can create access logs in the same standard format created by web servers,
    or in any number of custom formats.</p>

    <p>You can ask Catalina to create an access log for all requests
    processed by an <a href="engine.html">Engine</a>,
    <a href="host.html">Host</a>, or <a href="context.html">Context</a>
    by nesting a <a href="valve.html">Valve</a> element like this:</p>

<source>
&lt;Context&gt;
  ...
  &lt;Valve className="org.apache.catalina.valves.AccessLogValve"
         prefix="localhost_access_log." suffix=".txt"
         pattern="common"/&gt;
  ...
&lt;/Context&gt;
</source>

    <p>See <a href="valve.html#Access Log Valve">Access Log Valve</a>
    for more information on the configuration attributes that are
    supported.</p>

  </subsection>


  <subsection name="Automatic Context Configuration">

    <p>If you use the standard <strong>Context</strong> implementation,
    the following configuration steps occur automatically when Catalina
    is started, or whenever this web application is reloaded.  No special
    configuration is required to enable this feature.</p>
    
    <ul>
    <li>If you have not declared your own <a href="loader.html">Loader</a>
       element, a standard web application class loader will be configured.
       </li>
    <li>If you have not declared your own <a href="manager.html">Manager</a>
        element, a standard session manager will be configured.</li>
    <li>If you have not declared your own <a href="resources.html">Resources</a>
        element, a standard resources manager will be configured.</li>
    <li>The web application properties listed in <code>conf/web.xml</code>
        will be processed as defaults for this web application.  This is used
        to establish default mappings (such as mapping the <code>*.jsp</code>
        extension to the corresponding JSP servlet), and other standard
        features that apply to all web applications.</li>
    <li>The web application properties listed in the
        <code>/WEB-INF/web.xml</code> resource for this web application
        will be processed (if this resource exists).</li>
    <li>If your web application has specified security constraints that might
        require user authentication, an appropriate Authenticator that
        implements the login method you have selected will be configured.</li>
    </ul>

  </subsection>


  <subsection name="Context Parameters">

    <p>You can configure named values that will be made visible to the
    web application as servlet context initialization parameters by nesting
    <code>&lt;Parameter&gt;</code> elements inside this element.  For
    example, you can create an initialization parameter like this:</p>
<source>
&lt;Context&gt;
  ...
  &lt;Parameter name="companyName" value="My Company, Incorporated"
         override="false"/&gt;
  ...
&lt;/Context&gt;
</source>

    <p>This is equivalent to the inclusion of the following element in the
    web application deployment descriptor (<code>/WEB-INF/web.xml</code>):
    </p>
<source>
&lt;context-param&gt;
  &lt;param-name&gt;companyName&lt;/param-name&gt;
  &lt;param-value&gt;My Company, Incorporated&lt;/param-value&gt;
&lt;/context-param&gt;
</source>
    <p>but does <em>not</em> require modification of the deployment descriptor
    to customize this value.</p>

    <p>The valid attributes for a <code>&lt;Parameter&gt;</code> element
    are as follows:</p>

    <attributes>

      <attribute name="description" required="false">
        <p>Optional, human-readable description of this context
        initialization parameter.</p>
      </attribute>

      <attribute name="name" required="true">
        <p>The name of the context initialization parameter to be created.</p>
      </attribute>

      <attribute name="override" required="false">
        <p>Set this to <code>false</code> if you do <strong>not</strong> want
        a <code>&lt;context-param&gt;</code> for the same parameter name,
        found in the web application deployment descriptor, to override the
        value specified here.  By default, overrides are allowed.</p>
      </attribute>

      <attribute name="value" required="true">
        <p>The parameter value that will be presented to the application
        when requested by calling
        <code>ServletContext.getInitParameter()</code>.</p>
      </attribute>

    </attributes>

  </subsection>


  <subsection name="Environment Entries">

    <p>You can configure named values that will be made visible to the
    web application as environment entry resources, by nesting
    <code>&lt;Environment&gt;</code> entries inside this element.  For
    example, you can create an environment entry like this:</p>
<source>
&lt;Context&gt;
  ...
  &lt;Environment name="maxExemptions" value="10"
         type="java.lang.Integer" override="false"/&gt;
  ...
&lt;/Context&gt;
</source>

    <p>This is equivalent to the inclusion of the following element in the
    web application deployment descriptor (<code>/WEB-INF/web.xml</code>):
    </p>
<source>
&lt;env-entry&gt;
  &lt;env-entry-name&gt;maxExemptions&lt;/env-entry-name&gt;
  &lt;env-entry-value&gt;10&lt;/env-entry-value&gt;
  &lt;env-entry-type&gt;java.lang.Integer&lt;/env-entry-type&gt;
&lt;/env-entry&gt;
</source>
    <p>but does <em>not</em> require modification of the deployment descriptor
    to customize this value.</p>

    <p>The valid attributes for an <code>&lt;Environment&gt;</code> element
    are as follows:</p>

    <attributes>

      <attribute name="description" required="false">
        <p>Optional, human-readable description of this environment entry.</p>
      </attribute>

      <attribute name="name" required="true">
        <p>The name of the environment entry to be created, relative to the
        <code>java:comp/env</code> context.</p>
      </attribute>

      <attribute name="override" required="false">
        <p>Set this to <code>false</code> if you do <strong>not</strong> want
        an <code>&lt;env-entry&gt;</code> for the same environment entry name,
        found in the web application deployment descriptor, to override the
        value specified here.  By default, overrides are allowed.</p>
      </attribute>

      <attribute name="type" required="true">
        <p>The fully qualified Java class name expected by the web application
        for this environment entry.  Must be one of the legal values for
        <code>&lt;env-entry-type&gt;</code> in the web application deployment
        descriptor:  <code>java.lang.Boolean</code>,
        <code>java.lang.Byte</code>, <code>java.lang.Character</code>,
        <code>java.lang.Double</code>, <code>java.lang.Float</code>,
        <code>java.lang.Integer</code>, <code>java.lang.Long</code>,
        <code>java.lang.Short</code>, or <code>java.lang.String</code>.</p>
      </attribute>

      <attribute name="value" required="true">
        <p>The parameter value that will be presented to the application
        when requested from the JNDI context.  This value must be convertable
        to the Java type defined by the <code>type</code> attribute.</p>
      </attribute>

    </attributes>

  </subsection>


  <subsection name="Lifecycle Listeners">

    <p>If you have implemented a Java object that needs to know when this
    <strong>Context</strong> is started or stopped, you can declare it by
    nesting a <strong>Listener</strong> element inside this element.  The
    class name you specify must implement the
    <code>org.apache.catalina.LifecycleListener</code> interface, and
    the class must be packaged in a jar and placed in the 
    <code>$CATALINA_HOME/lib</code> directory. 
    It will be notified about the occurrence of the corresponding
    lifecycle events.  Configuration of such a listener looks like this:</p>

<source>
&lt;Context&gt;
  ...
  &lt;Listener className="com.mycompany.mypackage.MyListener" ... &gt;
  ...
&lt;/Context&gt;
</source>

    <p>Note that a Listener can have any number of additional properties
    that may be configured from this element.  Attribute names are matched
    to corresponding JavaBean property names using the standard property
    method naming patterns.</p>

  </subsection>


  <subsection name="Request Filters">

    <p>You can ask Catalina to check the IP address, or host name, on every
    incoming request directed to the surrounding
    <a href="engine.html">Engine</a>, <a href="host.html">Host</a>, or
    <a href="context.html">Context</a> element.  The remote address or name
    will be checked against a configured list of "accept" and/or "deny"
    filters, which are defined using <code>java.util.regex</code> Regular
    Expression syntax.  Requests that come from locations that are
    not accepted will be rejected with an HTTP "Forbidden" error.
    Example filter declarations:</p>

<source>
&lt;Context&gt;
  ...
  &lt;Valve className="org.apache.catalina.valves.RemoteHostValve"
         allow=".*\.mycompany\.com|www\.yourcompany\.com"/&gt;
  &lt;Valve className="org.apache.catalina.valves.RemoteAddrValve"
         deny="192\.168\.1\.\d+"/&gt;
  ...
&lt;/Context&gt;
</source>

    <p>See <a href="valve.html#Remote Address Filter">Remote Address Filter</a>
    and <a href="valve.html#Remote Host Filter">Remote Host Filter</a> for
    more information about the configuration options that are supported.</p>

  </subsection>


  <subsection name="Resource Definitions">

    <p>You can declare the characteristics of the resource
    to be returned for JNDI lookups of <code>&lt;resource-ref&gt;</code> and
    <code>&lt;resource-env-ref&gt;</code> elements in the web application
    deployment descriptor.  You <strong>MUST</strong> also define
    the needed resource parameters as attributes of the <code>Resource</code> 
    element, to configure the object factory to be used (if not known to Tomcat 
    already), and the properties used to configure that object factory.</p>

    <p>For example, you can create a resource definition like this:</p>
<source>
&lt;Context&gt;
  ...
  &lt;Resource name="jdbc/EmployeeDB" auth="Container"
            type="javax.sql.DataSource"
     description="Employees Database for HR Applications"/&gt;
  ...
&lt;/Context&gt;
</source>

    <p>This is equivalent to the inclusion of the following element in the
    web application deployment descriptor (<code>/WEB-INF/web.xml</code>):</p>
<source>
&lt;resource-ref&gt;
  &lt;description&gt;Employees Database for HR Applications&lt;/description&gt;
  &lt;res-ref-name&gt;jdbc/EmployeeDB&lt;/res-ref-name&gt;
  &lt;res-ref-type&gt;javax.sql.DataSource&lt;/res-ref-type&gt;
  &lt;res-auth&gt;Container&lt;/res-auth&gt;
&lt;/resource-ref&gt;
</source>

    <p>but does <em>not</em> require modification of the deployment
    descriptor to customize this value.</p>

    <p>The valid attributes for a <code>&lt;Resource&gt;</code> element
    are as follows:</p>

    <attributes>

      <attribute name="auth" required="false">
        <p>Specify whether the web Application code signs on to the
        corresponding resource manager programatically, or whether the
        Container will sign on to the resource manager on behalf of the
        application.  The value of this attribute must be
        <code>Application</code> or <code>Container</code>.  This
        attribute is <strong>required</strong> if the web application
        will use a <code>&lt;resource-ref&gt;</code> element in the web
        application deployment descriptor, but is optional if the
        application uses a <code>&lt;resource-env-ref&gt;</code> instead.</p>
      </attribute>

      <attribute name="description" required="false">
        <p>Optional, human-readable description of this resource.</p>
      </attribute>

      <attribute name="name" required="true">
        <p>The name of the resource to be created, relative to the
        <code>java:comp/env</code> context.</p>
      </attribute>

      <attribute name="scope" required="false">
        <p>Specify whether connections obtained through this resource
        manager can be shared.  The value of this attribute must be
        <code>Shareable</code> or <code>Unshareable</code>.  By default,
        connections are assumed to be shareable.</p>
      </attribute>

      <attribute name="type" required="true">
        <p>The fully qualified Java class name expected by the web
        application when it performs a lookup for this resource.</p>
      </attribute>

    </attributes>


  </subsection>


  <subsection name="Resource Links">

     <p>This element is used to create a link to a global JNDI resource. Doing
     a JNDI lookup on the link name will then return the linked global 
     resource.</p>

    <p>For example, you can create a resource link like this:</p>
<source>
&lt;Context&gt;
  ...
  &lt;ResourceLink name="linkToGlobalResource"
            global="simpleValue"
            type="java.lang.Integer"
  ...
&lt;/Context&gt;
</source>

    <p>The valid attributes for a <code>&lt;ResourceLink&gt;</code> element
    are as follows:</p>

    <attributes>

      <attribute name="global" required="true">
        <p>The name of the linked global resource in the 
        global JNDI context.</p>
      </attribute>

      <attribute name="name" required="true">
        <p>The name of the resource link to be created, relative to the
        <code>java:comp/env</code> context.</p>
      </attribute>

      <attribute name="type" required="true">
        <p>The fully qualified Java class name expected by the web
        application when it performs a lookup for this resource link.</p>
      </attribute>

      <attribute name="factory" required="false">
        <p>The fully qualified Java class name for the class creating these objects.
        This class should implement the <code>javax.naming.spi.ObjectFactory</code> interface.</p>
      </attribute>
    </attributes>

    <p>When the attribute <code>factory=&quot;org.apache.naming.factory.DataSourceLinkFactory&quot;</code> the resource link can be used with
       two additional attributes to allow a shared data source to be used with different credentials.
       When these two additional attributes are used in combination with the <code>javax.sql.DataSource</code>
       type, different contexts can share a global data source with different credentials.
       Under the hood, what happens is that a call to <a href="http://docs.oracle.com/javase/6/docs/api/javax/sql/DataSource.html#getConnection()"><code>getConnection()</code></a>
       is simply translated to a call <a href="http://docs.oracle.com/javase/6/docs/api/javax/sql/DataSource.html#getConnection(java.lang.String,%20java.lang.String)">
       <code>getConnection(username, password)</code></a> on the global data source. This is an easy way to get code to be transparent to what schemas are being used,
       yet be able to control connections (or pools) in the global configuration. 
    </p>
    <attributes>

      <attribute name="username" required="false">
        <p><code>username</code> value for the <code>getConnection(username, password)</code>
           call on the linked global DataSource.
        </p>
      </attribute>

      <attribute name="password" required="false">
        <p><code>password</code> value for the <code>getConnection(username, password)</code>
           call on the linked global DataSource.
        </p>
      </attribute>

    </attributes>
    <p>Shared Data Source Example:</p>
    <p><strong>Warning:</strong> This feature works only if the global DataSource
supports <code>getConnection(username, password)</code> method.
<a href="http://commons.apache.org/dbcp/">Apache Commons DBCP</a> pool that
Tomcat uses by default does not support it. See its Javadoc for
<code>BasicDataSource</code> class.
<a href="http://tomcat.apache.org/tomcat-7.0-doc/jdbc-pool.html">Apache Tomcat JDBC pool</a>
(included with Tomcat 7 and later) does support it,
but by default this support is disabled and can be enabled by
<code>alternateUsernameAllowed</code> attribute. See its documentation
for details. The example below uses Apache Tomcat JDBC pool.</p>
<source>
&lt;GlobalNamingResources&gt;
  ...
  &lt;Resource name=&quot;sharedDataSource&quot;
            global=&quot;sharedDataSource&quot;
            type=&quot;javax.sql.DataSource&quot;
            factory=&quot;org.apache.tomcat.jdbc.pool.DataSourceFactory&quot;
            alternateUsernameAllowed=&quot;true&quot;
            username=&quot;bar&quot;
            password=&quot;barpass&quot;
            ...
  ...
&lt;/GlobalNamingResources&gt;

&lt;Context path=&quot;/foo&quot;...&gt;
  ...
  &lt;ResourceLink 
            name=&quot;appDataSource&quot;
            global=&quot;sharedDataSource&quot;
            type=&quot;javax.sql.DataSource&quot;
            factory=&quot;org.apache.naming.factory.DataSourceLinkFactory&quot;
            username=&quot;foo&quot;
            password=&quot;foopass&quot;
  ...
&lt;/Context&gt;
&lt;Context path=&quot;/bar&quot;...&gt;
  ...
  &lt;ResourceLink 
            name=&quot;appDataSource&quot;
            global=&quot;sharedDataSource&quot;
            type=&quot;javax.sql.DataSource&quot;
  ...
&lt;/Context&gt;
</source>    
    <p>When a request for <code>getConnection()</code> is made in the <code>/foo</code> context, the request is translated into
       <code>getConnection(&quot;foo&quot;,&quot;foopass&quot;)</code>, while a request in the <code>/bar</code> gets passed straight through.</p>
  </subsection>

  <subsection name="Transaction">

    <p>You can declare the characteristics of the UserTransaction
    to be returned for JNDI lookup for <code>java:comp/UserTransaction</code>. 
    You <strong>MUST</strong> define an object factory class to instantiate
    this object as well as the needed resource parameters as attributes of the 
    <code>Transaction</code> 
    element, and the properties used to configure that object factory.</p>

    <p>The valid attributes for the <code>&lt;Transaction&gt;</code> element
    are as follows:</p>

    <attributes>

      <attribute name="factory" required="true">
        <p>The class name for the JNDI object factory.</p>
      </attribute>

    </attributes>

  </subsection>

</section>


</body>


</document>
