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Tomcat example source code file (context.xml)
This example Tomcat source code file (context.xml) is included in the DevDaily.com
"Java Source Code
Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.
The Tomcat context.xml source code
<?xml version="1.0"?>
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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
<title>The Context Container
</properties>
<body>
<section name="Introduction">
<p>The Context element represents a web
application</em>, which is run within a particular virtual host.
Each web application is based on a <em>Web Application Archive
(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://java.sun.com/products/servlet/download.html">Servlet
Specification</a>, and review the Tomcat
<a href="../appdev/index.html">Application Developer's Guide.
<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 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 file (which MUST
be located at <code>/WEB-INF/web.xml within the web app's
directory hierarchy).</p>
<p>You may define as many Context elements as you
wish. Each such Context MUST have a unique context path. In
addition, a Context must be present with a context path equal to
a zero-length string. This Context becomes the <em>default
web application for this virtual host, and is used to process all
requests that do not match any other Context's context path.</p>
<p>For Tomcat 6, unlike Tomcat 4.x, it is NOT recommended to place
<Context> elements directly in the server.xml file.</b> This
is because it makes modifing the <strong>Context configuration
more invasive since the main <code>conf/server.xml file cannot be
reloaded without restarting Tomcat.</p>
<p>Context elements may be explicitly defined:
<ul>
<li>in the $CATALINA_HOME/conf/context.xml file:
the Context element information will be loaded by all webapps</li>
<li>in the
<code>$CATALINA_HOME/conf/[enginename]/[hostname]/context.xml.default
file: the Context element information will be loaded by all webapps of that
host</li>
<li>in individual files (with a ".xml" extension) in the
<code>$CATALINA_HOME/conf/[enginename]/[hostname]/ directory.
The name of the file (less the .xml extension) will be used as the
context path. Multi-level context paths may be defined using #, e.g.
<code>context#path.xml. The default web application may be defined
by using a file called <code>ROOT.xml.
<li>if the previous file was not found for this application, in an individual
file at <code>/META-INF/context.xml inside the application files
<li>inside a Host element in the main
<code>conf/server.xml
</ul>
</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
for more information.</p>
<blockquote>
<p>The description below uses the variable name $CATALINA_HOME
to refer to the directory into which you have installed Tomcat 6,
and is the base directory against which most relative paths are
resolved. However, if you have configured Tomcat 6 for multiple
instances by setting a CATALINA_BASE directory, you should use
$CATALINA_BASE instead of $CATALINA_HOME for each of these
references.</p>
</em>
</section>
<section name="Attributes">
<subsection name="Common Attributes">
<p>All implementations of Context
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 interface.
If not specified, the standard value (defined below) will be used.</p>
</attribute>
<attribute name="cookies" required="false">
<p>Set to true if you want cookies to be used for
session identifier communication if supported by the client (this
is the default). Set to <code>false 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 true if you want calls within this application
to <code>ServletContext.getContext() to successfully return a
request dispatcher for other web applications running on this virtual
host. Set to <code>false (the default) in security
conscious environments, to make <code>getContext() always
return <code>null.
</attribute>
<attribute name="docBase" required="true">
<p>The Document Base (also known as the 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 directory of the
owning <a href="host.html">Host.
<p>The value of this field must not be set when the Context is
configured using a <code>META-INF/context.xml file as it will be
inferred by the automatic deployment process.</p>
</attribute>
<attribute name="override" required="false">
<p>Set to true to have explicit settings in this
Context element override any corresponding settings in the
<a href="defaultcontext.html">DefaultContext element associated
with our owning <a href="host.html">Host. By default, settings
in the DefaultContext element will be used.</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 conext. A context reload is not
sufficient.</p>
</attribute>
<attribute name="privileged" required="false">
<p>Set to true to allow this context to use container
servlets, like the manager servlet. Use of the <code>privileged
attribute will change the context's parent class loader to be the
<em>Server class loader rather than the Shared class
loader. Note that in a default installation, the <em>Common class
loader is used for both the <em>Server and the Shared
class loaders.</p>
</attribute>
<attribute name="path" required="false">
<p>The context path 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 must be unique.
If you specify a context path of an empty string (""), you are
defining the <em>default web application for this Host, which
will process all requests not assigned to other Contexts.</p>
<p>The value of this field must not be set except when statically
defining a Context in server.xml, as it will be inferred from the
filenames used for either the .xml context file or the docBase.</p>
</attribute>
<attribute name="reloadable" required="false">
<p>Set to true if you want Catalina to monitor classes in
<code>/WEB-INF/classes/ and /WEB-INF/lib 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. You
can use the <a href="../manager-howto.html">Manager web
application, however, to trigger reloads of deployed applications
on demand.</p>
</attribute>
<attribute name="wrapperClass" required="false">
<p>Java class name of the org.apache.catalina.Wrapper
implementation class that will be used for servlets managed by this
Context. If not specified, a standard default value will be used.</p>
</attribute>
</attributes>
</subsection>
<subsection name="Standard Implementation">
<p>The standard implementation of Context is
<strong>org.apache.catalina.core.StandardContext.
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 true, 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.
<p>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>
</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.
</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.
<p>Please note that setting this to true 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.
</p>
<p>
Please note that setting this flag to true in applications that are
outside the appBase for the Host (the <code>webapps directory
by default) will cause the application to be
<strong>deleted 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
(10 megabytes).</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
(5 seconds).</p>
</attribute>
<attribute name="cachingAllowed" required="false">
<p>If the value of this flag is true, the cache for static
resources will be used. If not specified, the default value
of the flag is <code>true.
</attribute>
<attribute name="caseSensitive" required="false">
<p>If the value of this flag is true, all case sensitivity
checks will be disabled. If not
specified, the default value of the flag is <code>true.
<p>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>
</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 true, 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.
</attribute>
<attribute name="tldNamespaceAware" required="false">
<p>If the value of this flag is true, the TLD files
XML validation will be namespace-aware. If you turn this flag on,
you should probably also turn <code>tldValidation on. The
default value for this flag is <code>false, and setting it
to true will incur a performance penalty.
</p>
</attribute>
<attribute name="tldValidation" required="false">
<p>If the value of this flag is true, the TLD files
will be XML validated on context startup. The default value for
this flag is <code>false, and setting it to true will incur
a performance penalty.</p>
</attribute>
<attribute name="unloadDelay" required="false">
<p>Amount of ms that the container will wait for servlets to unload.
If not specified, the default value of the flag is <code>2000
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.
</attribute>
<attribute name="useNaming" required="false">
<p>Set to true (the default) to have Catalina enable a
JNDI <code>InitialContext 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) named
<code>javax.servlet.context.tempdir as described in the
Servlet Specification. If not specified, a suitable directory
underneath <code>$CATALINA_HOME/work will be provided.
</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
element:</p>
<ul>
<li>Loader -
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>Manager -
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>Realm -
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 or Engine.
<li>Resources -
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>WatchedResource - 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]
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, 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 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 href="host.html">Host, or Context
by nesting a <a href="valve.html">Valve element like this:
<source>
<Context path="/examples" ...>
...
<Valve className="org.apache.catalina.valves.AccessLogValve"
prefix="localhost_access_log." suffix=".txt"
pattern="common"/>
...
</Context>
</source>
<p>See Access Log Valve
for more information on the configuration attributes that are
supported.</p>
</subsection>
<subsection name="Automatic Context Configuration">
<p>If you use the standard Context implementation,
the following configuration steps occur automtically 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 Loader
element, a standard web application class loader will be configured.
</li>
<li>If you have not declared your own Manager
element, a standard session manager will be configured.</li>
<li>If you have not declared your own Resources
element, a standard resources manager will be configured.</li>
<li>The web application properties listed in conf/web.xml
will be processed as defaults for this web application. This is used
to establish default mappings (such as mapping the <code>*.jsp
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 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><Parameter> elements inside this element. For
example, you can create an initialization parameter like this:</p>
<source>
<Context ...>
...
<Parameter name="companyName" value="My Company, Incorporated"
override="false"/>
...
</Context>
</source>
<p>This is equivalent to the inclusion of the following element in the
web application deployment descriptor (<code>/WEB-INF/web.xml):
</p>
<source>
<context-param>
<param-name>companyName</param-name>
<param-value>My Company, Incorporated</param-value>
</context-param>
</source>
<p>but does not require modification of the deployment descriptor
to customize this value.</p>
<p>The valid attributes for a <Parameter> 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.
</attribute>
<attribute name="override" required="false">
<p>Set this to false if you do not want
a <code><context-param> 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().
</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><Environment> entries inside this element. For
example, you can create an environment entry like this:</p>
<source>
<Context ...>
...
<Environment name="maxExemptions" value="10"
type="java.lang.Integer" override="false"/>
...
</Context>
</source>
<p>This is equivalent to the inclusion of the following element in the
web application deployment descriptor (<code>/WEB-INF/web.xml):
</p>
<source>
<env-entry>
<env-entry-name>maxExemptions</param-name>
<env-entry-value>10</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry>
</source>
<p>but does not require modification of the deployment descriptor
to customize this value.</p>
<p>The valid attributes for an <Environment> element
are as follows:</p>
<attributes>
<attribute name="description" required="false">
<p>Optional, human-readable description of this environment entry.
</attribute>
<attribute name="name" required="true">
<p>The name of the environment entry to be created, relative to the
<code>java:comp/env context.
</attribute>
<attribute name="override" required="false">
<p>Set this to false if you do not want
an <code><env-entry> 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><env-entry-type> in the web application deployment
descriptor: <code>java.lang.Boolean,
<code>java.lang.Byte, java.lang.Character,
<code>java.lang.Double, java.lang.Float,
<code>java.lang.Integer, java.lang.Long,
<code>java.lang.Short, or java.lang.String.
</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 attribute.
</attribute>
</attributes>
</subsection>
<subsection name="Lifecycle Listeners">
<p>If you have implemented a Java object that needs to know when this
<strong>Context is started or stopped, you can declare it by
nesting a <strong>Listener element inside this element. The
class name you specify must implement the
<code>org.apache.catalina.LifecycleListener interface, and
the class must be packaged in a jar and placed in the
<code>$CATALINA_HOME/lib directory.
It will be notified about the occurrence of the corresponding
lifecycle events. Configuration of such a listener looks like this:</p>
<source>
<Context path="/examples" ...>
...
<Listener className="com.mycompany.mypackage.MyListener" ... >
...
</Context>
</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, Host, or
<a href="context.html">Context element. The remote address or name
will be checked against a configured list of "accept" and/or "deny"
filters, which are defined using the Regular Expression syntax supported
by the <a href="http://jakarta.apache.org/regexp/">Jakarta Regexp
regular expression library. Requests that come from locations that are
not accepted will be rejected with an HTTP "Forbidden" error.
Example filter declarations:</p>
<source>
<Context path="/examples" ...>
...
<Valve className="org.apache.catalina.valves.RemoteHostValve"
allow="*.mycompany.com,www.yourcompany.com"/>
<Valve className="org.apache.catalina.valves.RemoteAddrValve"
deny="192.168.1.*"/>
...
</Context>
</source>
<p>See Remote Address Filter
and <a href="valve.html#Remote Host Filter">Remote Host Filter 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><resource-ref> and
<code><resource-env-ref> elements in the web application
deployment descriptor. You <strong>MUST also define
the needed resource parameters as attributes of the <code>Resource
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:
<source>
<Context ...>
...
<Resource name="jdbc/EmployeeDB" auth="Container"
type="javax.sql.DataSource"
description="Employees Database for HR Applications"/>
...
</Context>
</source>
<p>This is equivalent to the inclusion of the following element in the
web application deployment descriptor (<code>/WEB-INF/web.xml):
<source>
<resource-ref>
<description>Employees Database for HR Applications</description>
<res-ref-name>jdbc/EmployeeDB</res-ref-name>
<res-ref-type>javax.sql.DataSource</res-ref-type>
<res-auth>Container</res-auth>
</resource-ref>
</source>
<p>but does not require modification of the deployment
descriptor to customize this value.</p>
<p>The valid attributes for a <Resource> 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 or Container. This
attribute is <strong>required if the web application
will use a <code><resource-ref> element in the web
application deployment descriptor, but is optional if the
application uses a <code><resource-env-ref> instead.
</attribute>
<attribute name="description" required="false">
<p>Optional, human-readable description of this resource.
</attribute>
<attribute name="name" required="true">
<p>The name of the resource to be created, relative to the
<code>java:comp/env context.
</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 or Unshareable. 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:
<source>
<Context ...>
...
<ResourceLink name="linkToGlobalResource"
global="simpleValue"
type="java.lang.Integer"
...
</Context>
</source>
<p>The valid attributes for a <ResourceLink> 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 context.
</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>
</attributes>
</subsection>
<subsection name="Transaction">
<p>You can declare the characteristics of the UserTransaction
to be returned for JNDI lookup for <code>java:comp/UserTransaction.
You <strong>MUST define an object factory class to instantiate
this object as well as the needed resource parameters as attributes of the
<code>Transaction
element, and the properties used to configure that object factory.</p>
<p>The valid attributes for the <Transaction> element
are as follows:</p>
<attributes>
<attribute name="factory" required="true">
<p>The class name for the JNDI object factory.
</attribute>
</attributes>
</subsection>
</section>
</body>
</document>
Other Tomcat examples (source code examples)
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