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PageContext.javaAPI DocGlassfish v2 API20368Fri May 04 22:34:26 BST 2007javax.servlet.jsp

PageContext

public abstract class PageContext extends JspContext

PageContext extends JspContext to provide useful context information for when JSP technology is used in a Servlet environment.

A PageContext instance provides access to all the namespaces associated with a JSP page, provides access to several page attributes, as well as a layer above the implementation details. Implicit objects are added to the pageContext automatically.

The PageContext class is an abstract class, designed to be extended to provide implementation dependent implementations thereof, by conformant JSP engine runtime environments. A PageContext instance is obtained by a JSP implementation class by calling the JspFactory.getPageContext() method, and is released by calling JspFactory.releasePageContext().

An example of how PageContext, JspFactory, and other classes can be used within a JSP Page Implementation object is given elsewhere.

The PageContext provides a number of facilities to the page/component author and page implementor, including:

  • a single API to manage the various scoped namespaces
  • a number of convenience API's to access various public objects
  • a mechanism to obtain the JspWriter for output
  • a mechanism to manage session usage by the page
  • a mechanism to expose page directive attributes to the scripting environment
  • mechanisms to forward or include the current request to other active components in the application
  • a mechanism to handle errorpage exception processing

Methods Intended for Container Generated Code

Some methods are intended to be used by the code generated by the container, not by code written by JSP page authors, or JSP tag library authors.

The methods supporting lifecycle are initialize() and release()

The following methods enable the management of nested JspWriter streams to implement Tag Extensions: pushBody()

Methods Intended for JSP authors

The following methods provide convenient access to implicit objects: getException(), getPage() getRequest(), getResponse(), getSession(), getServletConfig() and getServletContext().

The following methods provide support for forwarding, inclusion and error handling: forward(), include(), and handlePageException().

Fields Summary
public static final int
PAGE_SCOPE
Page scope: (this is the default) the named reference remains available in this PageContext until the return from the current Servlet.service() invocation.
public static final int
REQUEST_SCOPE
Request scope: the named reference remains available from the ServletRequest associated with the Servlet until the current request is completed.
public static final int
SESSION_SCOPE
Session scope (only valid if this page participates in a session): the named reference remains available from the HttpSession (if any) associated with the Servlet until the HttpSession is invalidated.
public static final int
APPLICATION_SCOPE
Application scope: named reference remains available in the ServletContext until it is reclaimed.
public static final String
PAGE
Name used to store the Servlet in this PageContext's nametables.
public static final String
PAGECONTEXT
Name used to store this PageContext in it's own name table.
public static final String
REQUEST
Name used to store ServletRequest in PageContext name table.
public static final String
RESPONSE
Name used to store ServletResponse in PageContext name table.
public static final String
CONFIG
Name used to store ServletConfig in PageContext name table.
public static final String
SESSION
Name used to store HttpSession in PageContext name table.
public static final String
OUT
Name used to store current JspWriter in PageContext name table.
public static final String
APPLICATION
Name used to store ServletContext in PageContext name table.
public static final String
EXCEPTION
Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.
Constructors Summary
public PageContext()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Methods Summary
public abstract voidforward(java.lang.String relativeUrlPath)

This method is used to re-direct, or "forward" the current ServletRequest and ServletResponse to another active component in the application.

If the relativeUrlPath begins with a "/" then the URL specified is calculated relative to the DOCROOT of the ServletContext for this JSP. If the path does not begin with a "/" then the URL specified is calculated relative to the URL of the request that was mapped to the calling JSP.

It is only valid to call this method from a Thread executing within a _jspService(...) method of a JSP.

Once this method has been called successfully, it is illegal for the calling Thread to attempt to modify the ServletResponse object. Any such attempt to do so, shall result in undefined behavior. Typically, callers immediately return from _jspService(...) after calling this method.

param
relativeUrlPath specifies the relative URL path to the target resource as described above
throws
IllegalStateException if ServletResponse is not in a state where a forward can be performed
throws
ServletException if the page that was forwarded to throws a ServletException
throws
IOException if an I/O error occurred while forwarding

public ErrorDatagetErrorData()
Provides convenient access to error information.
return
an ErrorData instance containing information about the
error, as obtained from the request attributes, as per the
Servlet specification. If this is not an error page (that is,
if the isErrorPage attribute of the page directive is not set
to "true"), the information is meaningless.
since
JSP 2.0
	return new ErrorData( 
	    (Throwable)getRequest().getAttribute( "javax.servlet.error.exception" ),
	    ((Integer)getRequest().getAttribute( 
		"javax.servlet.error.status_code" )).intValue(),
	    (String)getRequest().getAttribute( "javax.servlet.error.request_uri" ),
	    (String)getRequest().getAttribute( "javax.servlet.error.servlet_name" ) );
    
public abstract java.lang.ExceptiongetException()
The current value of the exception object (an Exception).
return
any exception passed to this as an errorpage
public abstract java.lang.ObjectgetPage()
The current value of the page object (In a Servlet environment,
this is an instance of javax.servlet.Servlet).
return
the Page implementation class instance associated
with this PageContext
public abstract javax.servlet.ServletRequestgetRequest()
The current value of the request object (a ServletRequest).
return
The ServletRequest for this PageContext
public abstract javax.servlet.ServletResponsegetResponse()
The current value of the response object (a ServletResponse).
return
the ServletResponse for this PageContext
public abstract javax.servlet.ServletConfiggetServletConfig()
The ServletConfig instance.
return
the ServletConfig for this PageContext
public abstract javax.servlet.ServletContextgetServletContext()
The ServletContext instance.
return
the ServletContext for this PageContext
public abstract javax.servlet.http.HttpSessiongetSession()
The current value of the session object (an HttpSession).
return
the HttpSession for this PageContext or null
public abstract voidhandlePageException(java.lang.Exception e)

This method is intended to process an unhandled 'page' level
exception by forwarding the exception to the specified
error page for this JSP. If forwarding is not possible (for
example because the response has already been committed), an
implementation dependent mechanism should be used to invoke
the error page (e.g. "including" the error page instead).



If no error page is defined in the page, the exception should
be rethrown so that the standard servlet error handling
takes over.



A JSP implementation class shall typically clean up any local state
prior to invoking this and will return immediately thereafter. It is
illegal to generate any output to the client, or to modify any
ServletResponse state after invoking this call.



This method is kept for backwards compatiblity reasons. Newly
generated code should use PageContext.handlePageException(Throwable).
param
e the exception to be handled
throws
ServletException if an error occurs while invoking the error page
throws
IOException if an I/O error occurred while invoking the error
page
throws
NullPointerException if the exception is null
see
#handlePageException(Throwable)
public abstract voidhandlePageException(java.lang.Throwable t)

This method is intended to process an unhandled 'page' level
exception by forwarding the exception to the specified
error page for this JSP. If forwarding is not possible (for
example because the response has already been committed), an
implementation dependent mechanism should be used to invoke
the error page (e.g. "including" the error page instead).



If no error page is defined in the page, the exception should
be rethrown so that the standard servlet error handling
takes over.



This method is intended to process an unhandled "page" level exception
by redirecting the exception to either the specified error page for this
JSP, or if none was specified, to perform some implementation dependent
action.



A JSP implementation class shall typically clean up any local state
prior to invoking this and will return immediately thereafter. It is
illegal to generate any output to the client, or to modify any
ServletResponse state after invoking this call.
param
t the throwable to be handled
throws
ServletException if an error occurs while invoking the error page
throws
IOException if an I/O error occurred while invoking the error
page
throws
NullPointerException if the exception is null
see
#handlePageException(Exception)
public abstract voidinclude(java.lang.String relativeUrlPath)

Causes the resource specified to be processed as part of the current
ServletRequest and ServletResponse being processed by the calling Thread.
The output of the target resources processing of the request is written
directly to the ServletResponse output stream.




The current JspWriter "out" for this JSP is flushed as a side-effect
of this call, prior to processing the include.




If the  relativeUrlPath  begins with a "/" then the URL specified
is calculated relative to the DOCROOT of the ServletContext
for this JSP. If the path does not begin with a "/" then the URL
specified is calculated relative to the URL of the request that was
mapped to the calling JSP.




It is only valid to call this method from a  Thread 
executing within a  _jspService(...)  method of a JSP.

param
relativeUrlPath specifies the relative URL path to the target
resource to be included
throws
ServletException if the page that was forwarded to throws
a ServletException
throws
IOException if an I/O error occurred while forwarding
public abstract voidinclude(java.lang.String relativeUrlPath, boolean flush)

Causes the resource specified to be processed as part of the current
ServletRequest and ServletResponse being processed by the calling Thread.
The output of the target resources processing of the request is written
directly to the current JspWriter returned by a call to getOut().




If flush is true, The current JspWriter "out" for this JSP
is flushed as a side-effect of this call, prior to processing
the include. Otherwise, the JspWriter "out" is not flushed.




If the relativeUrlPath begins with a "/" then the URL specified
is calculated relative to the DOCROOT of the ServletContext
for this JSP. If the path does not begin with a "/" then the URL
specified is calculated relative to the URL of the request that was
mapped to the calling JSP.




It is only valid to call this method from a  Thread 
executing within a  _jspService(...)  method of a JSP.

param
relativeUrlPath specifies the relative URL path to the
target resource to be included
param
flush True if the JspWriter is to be flushed before the include,
or false if not.
throws
ServletException if the page that was forwarded to throws
a ServletException
throws
IOException if an I/O error occurred while forwarding
since
JSP 2.0
public abstract voidinitialize(javax.servlet.Servlet servlet, javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, java.lang.String errorPageURL, boolean needsSession, int bufferSize, boolean autoFlush)

The initialize method is called to initialize an uninitialized PageContext
so that it may be used by a JSP Implementation class to service an
incoming request and response within it's _jspService() method.



This method is typically called from JspFactory.getPageContext() in
order to initialize state.



This method is required to create an initial JspWriter, and associate
the "out" name in page scope with this newly created object.



This method should not be used by page or tag library authors.
param
servlet The Servlet that is associated with this PageContext
param
request The currently pending request for this Servlet
param
response The currently pending response for this Servlet
param
errorPageURL The value of the errorpage attribute from the page
directive or null
param
needsSession The value of the session attribute from the
page directive
param
bufferSize The value of the buffer attribute from the page
directive
param
autoFlush The value of the autoflush attribute from the page
directive
throws
IOException during creation of JspWriter
throws
IllegalStateException if out not correctly initialized
throws
IllegalArgumentException If one of the given parameters
is invalid
public javax.servlet.jsp.tagext.BodyContentpushBody()
Return a new BodyContent object, save the current "out" JspWriter,
and update the value of the "out" attribute in the page scope
attribute namespace of the PageContext.
return
the new BodyContent

                                                                                                                                                                                                                         
 
           
              
             
           

                                                                

       

                          

       

                                          

       


                        

       

                        

       

                           

       

                  

       

                   

       

                                                                                                                                                                                                                                           

         
          

                                                                                                                                                                                                      
         
          

                                                                                                                                                                                                                                               
           
	  

                                                                                                                                                                                               

         
          

                                                                                                                                                                                                                   

         
          

                                        

       
        return null; // XXX to implement
    
public abstract voidrelease()

This method shall "reset" the internal state of a PageContext, releasing
all internal references, and preparing the PageContext for potential
reuse by a later invocation of initialize(). This method is typically
called from JspFactory.releasePageContext().



Subclasses shall envelope this method.



This method should not be used by page or tag library authors.