Interface ServletContext
There is one context per "web application" per Java Virtual Machine. (A
"web application" is a collection of servlets and content installed under a
specific subset of the server's URL namespace such as /catalog
and possibly installed via a .war file.)
In the case of a web application marked "distributed" in its deployment descriptor, there will be one context instance for each virtual machine. In this situation, the context cannot be used as a location to share global information (because the information won't be truly global). Use an external resource like a database instead.
The ServletContext object is contained within
the ServletConfig object, which the Web server provides the
servlet when the servlet is initialized.
- Version:
- $Version$
- Author:
- Various
- See Also:
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Method Summary
Modifier and TypeMethodDescriptiongetAttribute(String name) Returns the servlet container attribute with the given name, ornullif there is no attribute by that name.Returns anEnumerationcontaining the attribute names available within this servlet context.getContext(String uripath) Returns aServletContextobject that corresponds to a specified URL on the server.getInitParameter(String name) Returns aStringcontaining the value of the named context-wide initialization parameter, ornullif the parameter does not exist.Returns the names of the context's initialization parameters as anEnumerationofStringobjects, or an emptyEnumerationif the context has no initialization parameters.intReturns the major version of the Java Servlet API that this servlet container supports.getMimeType(String file) Returns the MIME type of the specified file, ornullif the MIME type is not known.intReturns the minor version of the Servlet API that this servlet container supports.getNamedDispatcher(String name) Returns aRequestDispatcherobject that acts as a wrapper for the named servlet.getRealPath(String path) Returns aStringcontaining the real path for a given virtual path.getRequestDispatcher(String path) Returns aRequestDispatcherobject that acts as a wrapper for the resource located at the given path.getResource(String path) Returns a URL to the resource that is mapped to a specified path.getResourceAsStream(String path) Returns the resource located at the named path as anInputStreamobject.getResourcePaths(String path) Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument.Returns the name and version of the servlet container on which the servlet is running.getServlet(String name) Returns the name of this web application correponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.voidvoidWrites the specified message to a servlet log file, usually an event log.voidWrites an explanatory message and a stack trace for a givenThrowableexception to the servlet log file.voidremoveAttribute(String name) Removes the attribute with the given name from the servlet context.voidsetAttribute(String name, Object object) Binds an object to a given attribute name in this servlet context.
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Method Details
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getContext
Returns aServletContextobject that corresponds to a specified URL on the server.This method allows servlets to gain access to the context for various parts of the server, and as needed obtain
RequestDispatcherobjects from the context. The given path must be begin with "/", is interpreted relative to the server's document root and is matched against the context roots of other web applications hosted on this container.In a security conscious environment, the servlet container may return
nullfor a given URL.- Parameters:
uripath- aStringspecifying the context path of another web application in the container.- Returns:
- the
ServletContextobject that corresponds to the named URL, or null if either none exists or the container wishes to restrict this access. - See Also:
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getMajorVersion
int getMajorVersion()Returns the major version of the Java Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 2.- Returns:
- 2
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getMinorVersion
int getMinorVersion()Returns the minor version of the Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 3.- Returns:
- 3
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getMimeType
Returns the MIME type of the specified file, ornullif the MIME type is not known. The MIME type is determined by the configuration of the servlet container, and may be specified in a web application deployment descriptor. Common MIME types are"text/html"and"image/gif".- Parameters:
file- aStringspecifying the name of a file- Returns:
- a
Stringspecifying the file's MIME type
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getResourcePaths
Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument. Paths indicating subdirectory paths end with a '/'. The returned paths are all relative to the root of the web application and have a leading '/'. For example, for a web application containing
/welcome.html
/catalog/index.html
/catalog/products.html
/catalog/offers/books.html
/catalog/offers/music.html
/customer/login.jsp
/WEB-INF/web.xml
/WEB-INF/classes/com.acme.OrderServlet.class,
getResourcePaths("/") returns {"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}
getResourcePaths("/catalog/") returns {"/catalog/index.html", "/catalog/products.html", "/catalog/offers/"}.- Parameters:
the- partial path used to match the resources, which must start with a /- Returns:
- a Set containing the directory listing, or null if there are no resources in the web application whose path begins with the supplied path.
- Since:
- Servlet 2.3
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getResource
Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a local or remote file system, in a database, or in a
.warfile.The servlet container must implement the URL handlers and
URLConnectionobjects that are necessary to access the resource.This method returns
nullif no resource is mapped to the pathname.Some containers may allow writing to the URL returned by this method using the methods of the URL class.
The resource content is returned directly, so be aware that requesting a
.jsppage returns the JSP source code. Use aRequestDispatcherinstead to include results of an execution.This method has a different purpose than
java.lang.Class.getResource, which looks up resources based on a class loader. This method does not use class loaders.- Parameters:
path- aStringspecifying the path to the resource- Returns:
- the resource located at the named path,
or
nullif there is no resource at that path - Throws:
MalformedURLException- if the pathname is not given in the correct form
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getResourceAsStream
Returns the resource located at the named path as anInputStreamobject.The data in the
InputStreamcan be of any type or length. The path must be specified according to the rules given ingetResource. This method returnsnullif no resource exists at the specified path.Meta-information such as content length and content type that is available via
getResourcemethod is lost when using this method.The servlet container must implement the URL handlers and
URLConnectionobjects necessary to access the resource.This method is different from
java.lang.Class.getResourceAsStream, which uses a class loader. This method allows servlet containers to make a resource available to a servlet from any location, without using a class loader.- Parameters:
name- aStringspecifying the path to the resource- Returns:
- the
InputStreamreturned to the servlet, ornullif no resource exists at the specified path
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getRequestDispatcher
Returns aRequestDispatcherobject that acts as a wrapper for the resource located at the given path. ARequestDispatcherobject can be used to forward a request to the resource or to include the resource in a response. The resource can be dynamic or static.The pathname must begin with a "/" and is interpreted as relative to the current context root. Use
getContextto obtain aRequestDispatcherfor resources in foreign contexts. This method returnsnullif theServletContextcannot return aRequestDispatcher.- Parameters:
path- aStringspecifying the pathname to the resource- Returns:
- a
RequestDispatcherobject that acts as a wrapper for the resource at the specified path - See Also:
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getNamedDispatcher
Returns aRequestDispatcherobject that acts as a wrapper for the named servlet.Servlets (and JSP pages also) may be given names via server administration or via a web application deployment descriptor. A servlet instance can determine its name using
ServletConfig.getServletName().This method returns
nullif theServletContextcannot return aRequestDispatcherfor any reason.- Parameters:
name- aStringspecifying the name of a servlet to wrap- Returns:
- a
RequestDispatcherobject that acts as a wrapper for the named servlet - See Also:
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getServlet
- Throws:
ServletException
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getServlets
Enumeration getServlets() -
getServletNames
Enumeration getServletNames() -
log
Writes the specified message to a servlet log file, usually an event log. The name and type of the servlet log file is specific to the servlet container.- Parameters:
msg- aStringspecifying the message to be written to the log file
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log
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log
Writes an explanatory message and a stack trace for a givenThrowableexception to the servlet log file. The name and type of the servlet log file is specific to the servlet container, usually an event log.- Parameters:
message- aStringthat describes the error or exceptionthrowable- theThrowableerror or exception
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getRealPath
Returns aStringcontaining the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext..The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns
nullif the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a.wararchive).- Parameters:
path- aStringspecifying a virtual path- Returns:
- a
Stringspecifying the real path, or null if the translation cannot be performed
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getServerInfo
String getServerInfo()Returns the name and version of the servlet container on which the servlet is running.The form of the returned string is servername/versionnumber. For example, the JavaServer Web Development Kit may return the string
JavaServer Web Dev Kit/1.0.The servlet container may return other optional information after the primary string in parentheses, for example,
JavaServer Web Dev Kit/1.0 (JDK 1.1.6; Windows NT 4.0 x86).- Returns:
- a
Stringcontaining at least the servlet container name and version number
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getInitParameter
Returns aStringcontaining the value of the named context-wide initialization parameter, ornullif the parameter does not exist.This method can make available configuration information useful to an entire "web application". For example, it can provide a webmaster's email address or the name of a system that holds critical data.
- Parameters:
name- aStringcontaining the name of the parameter whose value is requested- Returns:
- a
Stringcontaining at least the servlet container name and version number - See Also:
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getInitParameterNames
Enumeration getInitParameterNames()Returns the names of the context's initialization parameters as anEnumerationofStringobjects, or an emptyEnumerationif the context has no initialization parameters.- Returns:
- an
EnumerationofStringobjects containing the names of the context's initialization parameters - See Also:
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getAttribute
Returns the servlet container attribute with the given name, ornullif there is no attribute by that name. An attribute allows a servlet container to give the servlet additional information not already provided by this interface. See your server documentation for information about its attributes. A list of supported attributes can be retrieved usinggetAttributeNames.The attribute is returned as a
java.lang.Objector some subclass. Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matchingjava.*,javax.*, andsun.*.- Parameters:
name- aStringspecifying the name of the attribute- Returns:
- an
Objectcontaining the value of the attribute, ornullif no attribute exists matching the given name - See Also:
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getAttributeNames
Enumeration getAttributeNames()Returns anEnumerationcontaining the attribute names available within this servlet context. Use thegetAttribute(java.lang.String)method with an attribute name to get the value of an attribute.- Returns:
- an
Enumerationof attribute names - See Also:
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setAttribute
Binds an object to a given attribute name in this servlet context. If the name specified is already used for an attribute, this method will replace the attribute with the new to the new attribute.If listeners are configured on the
ServletContextthe container notifies them accordingly.If a null value is passed, the effect is the same as calling
removeAttribute().Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matching
java.*,javax.*, andsun.*.- Parameters:
name- aStringspecifying the name of the attributeobject- anObjectrepresenting the attribute to be bound
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removeAttribute
Removes the attribute with the given name from the servlet context. After removal, subsequent calls togetAttribute(java.lang.String)to retrieve the attribute's value will returnnull.If listeners are configured on the
ServletContextthe container notifies them accordingly.- Parameters:
name- aStringspecifying the name of the attribute to be removed
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getServletContextName
String getServletContextName()Returns the name of this web application correponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.- Returns:
- The name of the web application or null if no name has been declared in the deployment descriptor.
- Since:
- Servlet 2.3
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