The Apache Tomcat Servlet/JSP Container

Apache Tomcat 7

Version 7.0.42, Jul 2 2013
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The Context Container

Table of Contents
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 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.

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 by the web application deployment.

You may define as many Context elements as you wish. Each such Context MUST have a unique context name within a virtual host. The context path does not need to be unique (see parallel deployment below). 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.

Parallel deployment

You may deploy multiple versions of a web application with the same context path at the same time. The rules used to match requests to a context version are as follows:

  • If no session information is present in the request, use the latest version.
  • If session information is present in the request, check the session manager of each version for a matching session and if one is found, use that version.
  • If session information is present in the request but no matching session can be found, use the latest version.

The Host may be configured (via the undeployOldVersions) to remove old versions deployed in this way once they are no longer in use.

Naming

When autoDeploy or deployOnStartup operations are performed by a Host, the name and context path of the web application are derived from the name(s) of the file(s) that define(s) the web application. Consequently, the context path may not be defined in a META-INF/context.xml embedded in the application and there is a close relationship between the context name, context path, context version and the base file name (the name minus any .war or .xml extension) of the file.

If no version is specified then the context name is always the same as the context path. If the context path is the empty string them the base name will be ROOT (always in upper case) otherwise the base name will be the context path with the leading '/' removed and any remaining '/' characters replaced with '#'.

If a version is specified then the context path remains unchanged and both the context name and the base name have the string '##' appended to them followed by the version identifier.

Some examples of these naming conventions are given below.

Context Path Context Version Context Name Base File Name Example File Names (.xml, .war & directory)
/foo None /foo foo foo.xml, foo.war, foo
/foo/bar None /foo/bar foo#bar foo#bar.xml, foo#bar.war, foo#bar
Empty String None Empty String ROOT ROOT.xml, ROOT.war, ROOT
/foo 42 /foo##42 foo##42 foo##42.xml, foo##42.war, foo##42
/foo/bar 42 /foo/bar##42 foo#bar##42 foo#bar##42.xml, foo#bar##42.war, foo#bar##42
Empty String 42 ##42 ROOT##42 ROOT##42.xml, ROOT##42.war, ROOT##42

The version component is treated as a String both for performance reasons and to allow flexibility in versioning schemes. String comparisons are used to determine version order. If version is not specified, it is treated as the empty string. Therefore, foo.war will be treated as an earlier version than foo##11.war and foo##11.war will be treated as an earlier version than foo##2.war. If using a purely numerical versioning scheme it is recommended that zero padding is used so that foo##002.war is treated as an earlier version than foo##011.war.

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. Optionally (based on the Host's copyXML attribute) this may be copied to $CATALINA_BASE/conf/[enginename]/[hostname]/ and renamed to application's base file name plus a ".xml" extension.
  • In individual files (with a ".xml" extension) in the $CATALINA_BASE/conf/[enginename]/[hostname]/ directory. The context path and version 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:

AttributeDescription
allowCasualMultipartParsing

Set to true if Tomcat should automatically parse multipart/form-data request bodies when HttpServletRequest.getPart* or HttpServletRequest.getParameter* is called, even when the target servlet isn't marked with the @MultipartConfig annotation (See Servlet Specification 3.0, Section 3.2 for details). Note that any setting other than false causes Tomcat to behave in a way that is not technically spec-compliant. The default is false

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.

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.

fireRequestListenersOnForwards

Set to true to fire any configured ServletRequestListeners when Tomcat forwards a request. This is primarily of use to users of CDI frameworks that use ServletRequestListeners to configure the necessary environment for a request. If not specified, the default value of false is used.

logEffectiveWebXml

Set to true if you want the effective web.xml used for a web application to be logged (at INFO level) when the application starts. The effective web.xml is the result of combining the application's web.xml with any defaults configured by Tomcat and any web-fragment.xml files and annotations discovered. If not specified, the default value of false is used.

override

Set to true to ignore any settings in both the global or Host default contexts. By default, settings from a default context will be used but may be overridden by a setting the same attribute explicitly for the Context.

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.

preemptiveAuthentication

When set to true and the user presents credentials for a resource that is not protected by a security constraint, if the authenticator supports preemptive authentication (the standard authenticators provided with Tomcat do) then the user' credentials will be processed. If not specified, the default of falseis 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.

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.

resourceOnlyServlets

Comma separated list of Servlet names (as used in /WEB-INF/web.xml) that expect a resource to be present. Ensures that welcome files associated with Servlets that expect a resource to be present (such as the JSP Servlet) are not used when there is no resource present. This prevents issues caused by the clarification of welcome file mapping in section 10.10 of the Servlet 3.0 specification. If the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true, the default value of this attribute will be the empty string, else the default value will be jsp.

sendRedirectBody

If true, redirect responses will include a short response body that includes details of the redirect as recommended by RFC 2616. This is disabled by default since including a response body may cause problems for some application component such as compression filters.

sessionCookieDomain

The domain to be used for all session cookies created for this context. If set, this overrides any domain set by the web application. If not set, the value specified by the web application, if any, will be used.

sessionCookieName

The name to be used for all session cookies created for this context. If set, this overrides any name set by the web application. If not set, the value specified by the web application, if any, will be used, or the name JSESSIONID if the web application does not explicitly set one.

sessionCookiePath

The path to be used for all session cookies created for this context. If set, this overrides any path set by the web application. If not set, the value specified by the web application will be used, or the context path used if the web application does not explicitly set one. To configure all web application to use an empty path (this can be useful for portlet specification implementations) set this attribute to / in the global CATALINA_BASE/conf/context.xml file.

sessionCookiePathUsesTrailingSlash

Some browsers, such as IE, will send a session cookie for a context with a path of /foo with a request to /foobar. To prevent this, Tomcat will add a trailing slash to the path associated with the session cookie so, in the above example, the cookie path becomes /foo/. However, with a cookie path of /foo/, IE will no longer send the cookie with a request to /foo. This should not be a problem unless there is a servlet mapped to /*. In this case this feature will need to be disabled. The default value for this attribute is true. To disable this feature, set the attribute to false.

swallowAbortedUploads

Set to false if Tomcat should not read any additional request body data for aborted uploads and instead abort the client connection. This setting is used in the following situations:

  • the size of the request body is larger than the maxPostSize configured in the connector
  • the size limit of a MultiPart upload is reached
  • the servlet sets the response status to 413 (Request Entity Too Large)

Not reading the additional data will free the request processing thread more quickly. Unfortunately most HTTP clients will not read the response if they can not write the full request.

The default is true, so additional data will be read.

Note if an error occurs during the request processing that triggers a 5xx response, any unread request data will always be ignored and the client connection will be closed once the error response has been written.

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. If the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true, the default value of this attribute will be true, else the default value will be false. Setting this attribute 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. If the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true, the default value of this attribute will be true, else the default value will be false. Setting this attribute to true will incur a performance penalty.

useHttpOnly

Should the HttpOnly flag be set on session cookies to prevent client side script from accessing the session ID? Defaults to true.

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.

xmlNamespaceAware

If the value of this flag is true, the validation of XML files will be namespace-aware. If you turn this flag on, you should probably also turn xmlValidation on. If the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true, the default value of this attribute will be true, else the default value will be false. Setting this attribute to true will incur a performance penalty.

xmlValidation

If the value of this flag is true, the XML files will be validated on context startup. If the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true, the default value of this attribute will be true, else the default value will be false. Setting this attribute to true will incur a performance penalty.

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):

AttributeDescription
addWebinfClassesResources

This attribute controls if, in addition to static resources being served from META-INF/resources inside web application JAR files, static resources are also served from WEB-INF/classes/META-INF/resources. This only applies to web applications with a major version of 3 or higher. Since this is a proprietary extension to the Servlet 3 specification, it is disabled by default. To enable this feature, set the attribute to true.

aliases

This attribute provides a list of external locations from which to load resources for this context. The list of aliases should be of the form "/aliasPath1=docBase1,/aliasPath2=docBase2" where aliasPathN must include a leading '/' and docBaseN must be an absolute path to either a .war file or a directory.

Whitespace is permitted around both the , and = delimiters, and will be trimmed. Therefore, an aliases attribute with the value "/aliasPath1 = docBase1,
/aliasPath2= docBase2"
is equivalent to "/aliasPath1=docBase1,/aliasPath2=docBase2"

A resource will be searched for in the first docBaseN for which aliasPathN is a leading path segment of the resource. If there is no such alias, then the resource will be searched in the usual way.

Using '/' as an aliasPath is not allowed. Consider using docBase instead.

These external locations will not be emptied if the context is un-deployed.

A more powerful feature (for development only) is Virtual webapp.

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.

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.

clearReferencesStatic

If true, Tomcat attempts to null out any static or final fields from loaded classes when a web application is stopped as a work around for apparent garbage collection bugs and application coding errors. There have been some issues reported with log4j when this is true. Applications without memory leaks using recent JVMs should operate correctly with this attribute set to false. If not specified, the default value of false 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.

jndiExceptionOnFailedWrite

If true, any attempt by an application to modify the provided JNDI context with a call to bind(), unbind(), createSubContext(), destroySubContext() or close() will trigger a javax.naming.OperationNotSupportedException as required by section EE.5.3.4 of the Java EE specification. This exception can be disabled by setting this attribute to true in which case any calls to modify the JNDI context will return without making any changes and methods that return values will return null. If not specified, the specification compliant default of true will be used.

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.

renewThreadsWhenStoppingContext

If true, when this context is stopped, Tomcat renews all the threads from the thread pool that was used to serve this context. This also requires that the ThreadLocalLeakPreventionListener be configured in server.xml and that the threadRenewalDelay property of the Executor be >=0. If not specified, the default value of true will be used.

unloadDelay

Number of ms that the container will wait for servlets to unload. If not specified, the default value is 2000 ms.

unpackWAR

If false, the unpackWARs attribute of the owning Host will be overridden and the WAR file will not be unpacked. If true, the value of the owning Host's unpackWARs attribute will determine if the WAR is unpacked. If not specified, the default value is true. Note that WAR files located outside of a Host's appBase are never unpacked.

useNaming

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