Links Top Level Elements Executors Connectors Containers Nested Components Cluster Elements Other | Apache Tomcat Configuration ReferenceThe Context Container| Introduction |
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.
The Context element represents a web
application, which is run within a particular virtual host.
Each web application is based on a 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
Servlet
Specification, and review the Tomcat
Application Developer's Guide.
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 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 web application deployment descriptor file (which MUST
be located at /WEB-INF/web.xml within the web app's
directory hierarchy).
You may define as many Context 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 default
web application for this virtual host, and is used to process all
requests that do not match any other Context's context path.
| Naming |
When autoDeploy or deployOnStartup operations
are performed by a Host, the web application is specified by a context XML
file in Host's xmlBase
directory or by a WAR file or a directory file in Host's
appBase directory.
In this case the context path is derived from the name of the file that
is being deployed. Consequently, the context path may not
be defined in a META-INF/context.xml embedded in
the application. There is, therefore, a close relationship between the
context path and
the base file name (the name minus .war or
.xml extension) of the file.
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:
- If the context path is a zero length string, the base name is
"ROOT" (uppercase)
- If the context path is not a zero length string, the base
name is the context path with the leading '/' removed and any
remaining '/' characters in the path replaced with '#'.
To help clarify these rules, some examples are given in the following
table.
| Context Path |
Base File Name |
| /foo | foo |
| /foo/bar | foo#bar |
| Empty String |
ROOT |
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:
- Disable autoDeploy and deployOnStartup and define all
Contexts in server.xml
- Locate the WAR and/or directory outside of the Host's appBase and use
a context.xml file with a docBase attribute to define it.
|
| Defining a context |
It is NOT recommended to place
<Context> elements directly in the server.xml file. This
is because it makes modifying the Context configuration
more invasive since the main conf/server.xml file cannot be
reloaded without restarting Tomcat.
Individual Context elements may be explicitly defined:
- In an individual file at
/META-INF/context.xml inside the
application files. In Tomcat 6 this file is automatically copied to
$CATALINA_BASE/conf/[enginename]/[hostname]/ and renamed to
application's base file name plus a ".xml" extension.
(This automated copying became optional in Tomcat 7).
- In individual files (with a ".xml" extension) in the
$CATALINA_BASE/conf/[enginename]/[hostname]/ 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's META-INF
directory.
- Inside a Host element in the main
conf/server.xml.
Default Context 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. <Resource> elements, that are defined in a default
Context will be created once for each
Context to which the default applies. They will not be
shared between Context elements.
- In the
$CATALINA_BASE/conf/context.xml file:
the Context element information will be loaded by all web applications.
- In the
$CATALINA_BASE/conf/[enginename]/[hostname]/context.xml.default
file: the Context element information will be loaded by all web applications
of that host.
With the exception of server.xml, files that define Context
elements may only define a single Context element.
In addition to explicitly specified Context elements, there are
several techniques by which Context elements can be created automatically
for you. See
Automatic Application Deployment and
User Web Applications
for more information.
To define multiple contexts that use a single WAR file or directory,
use one of the options described in the Naming
section above for creating a Context that has a path
that is not related to the base file name.
|
|
| Attributes |
| Common Attributes |
All implementations of Context
support the following attributes:
| Attribute | Description |
|---|
backgroundProcessorDelay |
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.
| className |
Java class name of the implementation to use. This class must
implement the org.apache.catalina.Context interface.
If not specified, the standard value (defined below) will be used.
| cookies |
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 false if you want to disable
the use of cookies for session identifier communication, and rely
only on URL rewriting by the application.
| crossContext |
Set to true if you want calls within this application
to ServletContext.getContext() to successfully return a
request dispatcher for other web applications running on this virtual
host. Set to false (the default) in security
conscious environments, to make getContext() always
return null.
| disableURLRewriting |
Set to true 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 must be a way to retain sessions if the
client doesn't allow session cookies. If not specified, the
specification compliant default value of false will be
used.
| docBase |
The Document Base (also known as the Context
Root) 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 appBase directory of the
owning Host.
The value of this field must not be set unless the Context element is
defined in server.xml or the docBase is not located under
the Host's appBase.
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.
| override |
Set to true to have explicit settings in this
Context element override any corresponding settings in either the global
or Host default contexts. By default, settings
from a default context will be used.
| privileged |
Set to true to allow this context to use container
servlets, like the manager servlet. Use of the privileged
attribute will change the context's parent class loader to be the
Server class loader rather than the Shared class
loader. Note that in a default installation, the Common class
loader is used for both the Server and the Shared
class loaders.
| path |
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 Host must be unique.
If you specify a context path of an empty string (""), you are
defining the default web application for this Host, which
will process all requests not assigned to other Contexts.
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.
Even when statically defining a Context in server.xml, this attribute
must not be set unless either the docBase is not located under the
Host's appBase or both
deployOnStartup and autoDeploy are false. If
this rule is not followed, double deployment is likely to result.
| reloadable |
Set to true if you want Catalina to monitor classes in
/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 false. You
can use the Manager web
application, however, to trigger reloads of deployed applications
on demand.
| sessionCookieDomain |
The domain to be used for all session cookies created for this
Context. If not set, no domain will be specified for session cookies.
| sessionCookieName |
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
org.apache.catalina.SESSION_COOKIE_NAME system
property.
| sessionCookiePath |
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 emptySessionPath attribute on the
connector used to access this Context.
| wrapperClass |
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.
| useHttpOnly |
Should the HttpOnly flag be set on session cookies to prevent client
side script from accessing the session ID? Defaults to
false.
|
|
| Standard Implementation |
The standard implementation of Context is
org.apache.catalina.core.StandardContext.
It supports the following additional attributes (in addition to the
common attributes listed above):
| Attribute | Description |
|---|
allowLinking |
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 false.
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.
| antiJARLocking |
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 false.
antiJARLocking is a subset of
antiResourceLocking and therefore, to prevent duplicate
work and possible issues, only one of these attributes should be set
to true at any one time.
| antiResourceLocking |
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 false.
antiJARLocking is a subset of
antiResourceLocking and therefore, to prevent duplicate
work and possible issues, only one of these attributes should be set
to true at any one time.
Please note that setting this to true has some side
effects, including the disabling of JSP reloading in a running server:
see
Bugzilla 37668.
Please note that setting this flag to true in applications that are
outside the appBase for the Host (the webapps directory
by default) will cause the application to be 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.
| cacheMaxSize |
Maximum size of the static resource cache in kilobytes.
If not specified, the default value is 10240
(10 megabytes).
| cacheObjectMaxSize |
Maximum size of the static resource that will be placed in the cache.
If not specified, the default value is 512
(512 kilobytes). If this value is greater than
cacheMaxSize/20 it will be reduced to
cacheMaxSize/20.
| cacheTTL |
Amount of time in milliseconds between cache entries revalidation.
If not specified, the default value is 5000
(5 seconds).
| cachingAllowed |
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 true.
| caseSensitive |
Deprecated. This option is removed in Tomcat 7
onwards where the default of true is always used.
If the value of this flag is false, all case sensitivity
checks will be disabled. If not
specified, the default value of the flag is true.
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.
| clearReferencesHttpClientKeepAliveThread |
If true and an sun.net.www.http.HttpClient
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 WebappClassLoader to
WebappClassLoader#parent 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
true will be used.
| clearReferencesStopThreads |
If true, Tomcat attempts to terminate threads that have
been started by the web application. Stopping threads is performed via
the deprecated (for good reason) Thread.stop() 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 false will be used.
| clearReferencesStopTimerThreads |
If true, Tomcat attempts to terminate
java.util.Timer 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 false will be used.
| clearReferencesThreadLocals |
If true, 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 false will be used since the clearing of the
ThreadLocal objects is not performed in a thread-safe manner.
| processTlds |
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.
| swallowOutput |
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 false.
| tldNamespaceAware |
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 tldValidation on. The
default value for this flag is false, and setting it
to true will incur a performance penalty.
| tldValidation |
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 false, and setting it to true will incur
a performance penalty.
| unloadDelay |
Number of ms that the container will wait for servlets to unload.
If not specified, the default value is 2000 ms.
| unpackWAR |
If true, Tomcat will unpack all compressed web applications before
running them.
If not specified, the default value is true.
| useNaming |
Set to true (the default) to have Catalina enable a
JNDI InitialContext for this web application that is
compatible with Java2 Enterprise Edition (J2EE) platform
conventions.
| workDir |
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
java.io.File) named
javax.servlet.context.tempdir as described in the
Servlet Specification. If not specified, a suitable directory
underneath $CATALINA_BASE/work will be provided.
|
|
|
| Nested Components |
You can nest at most one instance of the following utility components
by nesting a corresponding element inside your Context
element:
- 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.
- 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.
- 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
Host or Engine.
- 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.
- 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.
|
| Special Features |
| Logging |
A context is associated with the
org.apache.catalina.core.ContainerBase.[enginename].[hostname].[path]
log category. Note that the brackets are actually part of the name, don't omit them.
|
| Automatic Context Configuration |
If you use the standard Context 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.
- If you have not declared your own Loader
element, a standard web application class loader will be configured.
- If you have not declared your own Manager
element, a standard session manager will be configured.
- If you have not declared your own Resources
element, a standard resources manager will be configured.
- 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 *.jsp
extension to the corresponding JSP servlet), and other standard
features that apply to all web applications.
- The web application properties listed in the
/WEB-INF/web.xml resource for this web application
will be processed (if this resource exists).
- 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.
|
| Environment Entries |
You can configure named values that will be made visible to the
web application as environment entry resources, by nesting
<Environment> entries inside this element. For
example, you can create an environment entry like this:
 | | | |
<Context>
...
<Environment name="maxExemptions" value="10"
type="java.lang.Integer" override="false"/>
...
</Context>
| | | | |
This is equivalent to the inclusion of the following element in the
web application deployment descriptor (/WEB-INF/web.xml):
| | | |
<env-entry>
<env-entry-name>maxExemptions</env-entry-name>
<env-entry-value>10</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry>
| | | | |
but does not require modification of the deployment descriptor
to customize this value.
The valid attributes for an <Environment> element
are as follows:
| Attribute | Description |
|---|
description |
Optional, human-readable description of this environment entry.
| name |
The name of the environment entry to be created, relative to the
java:comp/env context.
| override |
Set this to false if you do not want
an <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.
| type |
The fully qualified Java class name expected by the web application
for this environment entry. Must be one of the legal values for
<env-entry-type> in the web application deployment
descriptor: java.lang.Boolean,
java.lang.Byte, java.lang.Character,
java.lang.Double, java.lang.Float,
java.lang.Integer, java.lang.Long,
java.lang.Short, or java.lang.String.
| value |
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 type attribute.
|
|
| Resource Links |
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.
For example, you can create a resource link like this:
| | | |
<Context>
...
<ResourceLink name="linkToGlobalResource"
global="simpleValue"
type="java.lang.Integer"
...
</Context>
| | | | |
The valid attributes for a <ResourceLink> element
are as follows:
| Attribute | Description |
|---|
global |
The name of the linked global resource in the
global JNDI context.
| name |
The name of the resource link to be created, relative to the
java:comp/env context.
| type |
The fully qualified Java class name expected by the web
application when it performs a lookup for this resource link.
| factory |
The fully qualified Java class name for the class creating these objects.
This class should implement the javax.naming.spi.ObjectFactory interface.
|
When the attribute factory="org.apache.naming.factory.DataSourceLinkFactory" 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 javax.sql.DataSource
type, different contexts can share a global data source with different credentials.
Under the hood, what happens is that a call to getConnection()
is simply translated to a call
getConnection(username, password) 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.
| Attribute | Description |
|---|
username |
username value for the getConnection(username, password)
call on the linked global DataSource.
| password |
password value for the getConnection(username, password)
call on the linked global DataSource.
|
Shared Data Source Example:
Warning: This feature works only if the global DataSource
supports getConnection(username, password) method.
Apache Commons DBCP pool that
Tomcat uses by default does not support it. See its Javadoc for
BasicDataSource class.
Apache Tomcat JDBC pool
(included with Tomcat 7 and later) does support it,
but by default this support is disabled and can be enabled by
alternateUsernameAllowed attribute. See its documentation
for details. The example below uses Apache Tomcat JDBC pool.
| | | |
<GlobalNamingResources>
...
<Resource name="sharedDataSource"
global="sharedDataSource"
type="javax.sql.DataSource"
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
alternateUsernameAllowed="true"
username="bar"
password="barpass"
...
...
</GlobalNamingResources>
<Context path="/foo"...>
...
<ResourceLink
name="appDataSource"
global="sharedDataSource"
type="javax.sql.DataSource"
factory="org.apache.naming.factory.DataSourceLinkFactory"
username="foo"
password="foopass"
...
</Context>
<Context path="/bar"...>
...
<ResourceLink
name="appDataSource"
global="sharedDataSource"
type="javax.sql.DataSource"
...
</Context>
| | | | |
When a request for getConnection() is made in the /foo context, the request is translated into
getConnection("foo","foopass"), while a request in the /bar gets passed straight through.
|
| Transaction |
You can declare the characteristics of the UserTransaction
to be returned for JNDI lookup for java:comp/UserTransaction.
You MUST define an object factory class to instantiate
this object as well as the needed resource parameters as attributes of the
Transaction
element, and the properties used to configure that object factory.
The valid attributes for the <Transaction> element
are as follows:
| Attribute | Description |
|---|
factory |
The class name for the JNDI object factory.
|
|
|
|
