javax.servlet
Interface ServletContext


@TransactionType(value=NOT_SUPPORTED)
public interface ServletContext

Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.

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.)

The ServletContext object is contained within the ServletConfig object, which the Web server provides the servlet when the servlet is initialized.

This Java Card interface is a subset of the Java Servlet API 2.4 ServletContext interface. Some methods have been pruned in an effort to reduce the size of this interface and its implementations and/or eliminate dependencies on unsupported features.

Since:
Servlet 2.x, Java Card 3.0
See Also:
Servlet.getServletConfig(), ServletConfig.getServletContext()

Method Summary
 Object getAttribute(String name)
          Returns the servlet container attribute with the given name, or null if there is no attribute by that name.
 Enumeration getAttributeNames()
          Returns an Enumeration containing the attribute names available within this servlet context.
 ServletContext getContext(String uripath)
          Returns a ServletContext object that corresponds to a specified URL on the server.
 String getInitParameter(String name)
          Returns a String containing the value of the named context-wide initialization parameter, or null if the parameter does not exist.
 Enumeration getInitParameterNames()
          Returns the names of the context's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the context has no initialization parameters.
 int getMajorVersion()
          Returns the major version of the Java Servlet API that this servlet container supports.
 String getMimeType(String file)
          Returns the MIME type of the specified file, or null if the MIME type is not known.
 int getMinorVersion()
          Returns the minor version of the Servlet API that this servlet container supports.
 RequestDispatcher getNamedDispatcher(String name)
          Returns a RequestDispatcher object that acts as a wrapper for the named servlet.
 String getRealPath(String path)
          Returns a String containing the real path for a given virtual path.
 RequestDispatcher getRequestDispatcher(String path)
          Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path.
 InputStream getResourceAsStream(String path)
          Returns the resource located at the named path as an InputStream object.
 String getServerInfo()
          Returns the name and version of the servlet container on which the servlet is running.
 String getServletContextName()
          Returns the name of this web application corresponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.
 void log(String msg)
          Writes the specified message to a servlet log file, usually an event log.
 void log(String message, Throwable throwable)
          Writes an explanatory message and a stack trace for a given Throwable exception to the servlet log file.
 void removeAttribute(String name)
          Removes the attribute with the given name from the servlet context.
 void setAttribute(String name, Object object)
          Binds an object to a given attribute name in this servlet context.
 

Method Detail

getContext

ServletContext getContext(String uripath)
Returns a ServletContext object 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 RequestDispatcher objects 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 null for a given URL.

Parameters:
uripath - a String specifying the context path of another web application in the container.
Returns:
the ServletContext object that corresponds to the named URL, or null if either none exists or the container wishes to restrict this access.
See Also:
RequestDispatcher

getMajorVersion

int getMajorVersion()
Returns the major version of the Java Servlet API that this servlet container supports. All implementations that comply with Version 2.4 must have this method return the integer 2.

Returns:
2

getMinorVersion

int getMinorVersion()
Returns the minor version of the Servlet API that this servlet container supports. All implementations that comply with Version 2.4 must have this method return the integer 4.

Returns:
4

getMimeType

String getMimeType(String file)
Returns the MIME type of the specified file, or null if 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 - a String specifying the name of a file
Returns:
a String specifying the file's MIME type

getResourceAsStream

InputStream getResourceAsStream(String path)
Returns the resource located at the named path as an InputStream object.

The data in the InputStream can be of any type or length. The path must begin with a "/" and is interpreted as relative to the current context root. This method returns null if no resource exists at the specified path.

This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a file system, in a database, or in a .war file.

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:
path - a String specifying the path to the resource
Returns:
the InputStream returned to the servlet, or null if no resource exists at the specified path

getRequestDispatcher

RequestDispatcher getRequestDispatcher(String path)
Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path. A RequestDispatcher object 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 getContext to obtain a RequestDispatcher for resources in foreign contexts. This method returns null if the ServletContext cannot return a RequestDispatcher.

Parameters:
path - a String specifying the pathname to the resource
Returns:
a RequestDispatcher object that acts as a wrapper for the resource at the specified path, or null if the ServletContext cannot return a RequestDispatcher
See Also:
RequestDispatcher, getContext(java.lang.String)

getNamedDispatcher

RequestDispatcher getNamedDispatcher(String name)
Returns a RequestDispatcher object that acts as a wrapper for the named servlet.

Servlets 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 null if the ServletContext cannot return a RequestDispatcher for any reason.

Parameters:
name - a String specifying the name of a servlet to wrap
Returns:
a RequestDispatcher object that acts as a wrapper for the named servlet, or null if the ServletContext cannot return a RequestDispatcher
See Also:
RequestDispatcher, getContext(java.lang.String), ServletConfig.getServletName()

log

void log(String msg)
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 - a String specifying the message to be written to the log file

log

void log(String message,
         Throwable throwable)
Writes an explanatory message and a stack trace for a given Throwable exception 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 - a String that describes the error or exception
throwable - the Throwable error or exception

getRealPath

String getRealPath(String path)
Returns a String containing 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 null if 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 .war archive).

Parameters:
path - a String specifying a virtual path
Returns:
a String specifying the real path, or null if the translation cannot be performed

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 String containing at least the servlet container name and version number

getInitParameter

String getInitParameter(String name)
Returns a String containing the value of the named context-wide initialization parameter, or null if 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 - a String containing the name of the parameter whose value is requested
Returns:
a String containing at least the servlet container name and version number
See Also:
ServletConfig.getInitParameter(java.lang.String)

getInitParameterNames

Enumeration getInitParameterNames()
Returns the names of the context's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the context has no initialization parameters.

Returns:
an Enumeration of String objects containing the names of the context's initialization parameters
See Also:
ServletConfig.getInitParameter(java.lang.String)

getAttribute

Object getAttribute(String name)
Returns the servlet container attribute with the given name, or null if 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 using getAttributeNames.

The attribute is returned as a java.lang.Object or some subclass. Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matching java.*, javax.*, javacard.*, javacardx.*, com.sun.*, and sun.*.

Parameters:
name - a String specifying the name of the attribute
Returns:
an Object containing the value of the attribute, or null if no attribute exists matching the given name
See Also:
getAttributeNames()

getAttributeNames

Enumeration getAttributeNames()
Returns an Enumeration containing the attribute names available within this servlet context. Use the getAttribute(java.lang.String) method with an attribute name to get the value of an attribute.

Returns:
an Enumeration of attribute names
See Also:
getAttribute(java.lang.String)

setAttribute

void setAttribute(String name,
                  Object object)
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 ServletContext the 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.*, javacard.*, javacardx.*, com.sun.*, and sun.*.

Parameters:
name - a String specifying the name of the attribute
object - an Object representing the attribute to be bound

removeAttribute

void removeAttribute(String name)
Removes the attribute with the given name from the servlet context. After removal, subsequent calls to getAttribute(java.lang.String) to retrieve the attribute's value will return null.

If listeners are configured on the ServletContext the container notifies them accordingly.

Parameters:
name - a String specifying the name of the attribute to be removed

getServletContextName

String getServletContextName()
Returns the name of this web application corresponding 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


Copyright (c) 2009 Sun Microsystems, Inc. All rights reserved.