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:
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().
| Modifier and Type | Field and Description | 
|---|---|
| static java.lang.String | APPLICATIONName used to store ServletContext in PageContext name table. | 
| static int | APPLICATION_SCOPEApplication scope: named reference remains available in the
 ServletContext until it is reclaimed. | 
| static java.lang.String | CONFIGName used to store ServletConfig in PageContext name table. | 
| static java.lang.String | EXCEPTIONName used to store uncaught exception in ServletRequest attribute
 list and PageContext name table. | 
| static java.lang.String | OUTName used to store current JspWriter in PageContext name table. | 
| static java.lang.String | PAGEName used to store the Servlet in this PageContext's nametables. | 
| static int | PAGE_SCOPEPage scope: (this is the default) the named reference remains available
 in this PageContext until the return from the current Servlet.service()
 invocation. | 
| static java.lang.String | PAGECONTEXTName used to store this PageContext in it's own name table. | 
| static java.lang.String | REQUESTName used to store ServletRequest in PageContext name table. | 
| static int | REQUEST_SCOPERequest scope: the named reference remains available from the
 ServletRequest associated with the Servlet until the current request
 is completed. | 
| static java.lang.String | RESPONSEName used to store ServletResponse in PageContext name table. | 
| static java.lang.String | SESSIONName used to store HttpSession in PageContext name table. | 
| static int | SESSION_SCOPESession 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. | 
| Constructor and Description | 
|---|
| PageContext()Sole constructor. | 
| Modifier and Type | Method and Description | 
|---|---|
| abstract void | forward(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. | 
| ErrorData | getErrorData()Provides convenient access to error information. | 
| abstract java.lang.Exception | getException()The current value of the exception object (an Exception). | 
| abstract java.lang.Object | getPage()The current value of the page object (In a Servlet environment,
 this is an instance of javax.servlet.Servlet). | 
| abstract javax.servlet.ServletRequest | getRequest()The current value of the request object (a ServletRequest). | 
| abstract javax.servlet.ServletResponse | getResponse()The current value of the response object (a ServletResponse). | 
| abstract javax.servlet.ServletConfig | getServletConfig()The ServletConfig instance. | 
| abstract javax.servlet.ServletContext | getServletContext()The ServletContext instance. | 
| abstract javax.servlet.http.HttpSession | getSession()The current value of the session object (an HttpSession). | 
| abstract void | handlePageException(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. | 
| abstract void | handlePageException(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. | 
| abstract void | include(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. | 
| abstract void | include(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. | 
| abstract void | initialize(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. | 
| BodyContent | pushBody()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. | 
| abstract void | release()
 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(). | 
findAttribute, getAttribute, getAttribute, getAttributeNamesInScope, getAttributesScope, getELContext, getExpressionEvaluator, getOut, getVariableResolver, popBody, pushBody, removeAttribute, removeAttribute, setAttribute, setAttributepublic static final int PAGE_SCOPE
public static final int REQUEST_SCOPE
public static final int SESSION_SCOPE
public static final int APPLICATION_SCOPE
public static final java.lang.String PAGE
public static final java.lang.String PAGECONTEXT
public static final java.lang.String REQUEST
public static final java.lang.String RESPONSE
public static final java.lang.String CONFIG
public static final java.lang.String SESSION
public static final java.lang.String OUT
public static final java.lang.String APPLICATION
public static final java.lang.String EXCEPTION
public PageContext()
public abstract void initialize(javax.servlet.Servlet servlet,
              javax.servlet.ServletRequest request,
              javax.servlet.ServletResponse response,
              java.lang.String errorPageURL,
              boolean needsSession,
              int bufferSize,
              boolean autoFlush)
                         throws java.io.IOException,
                                java.lang.IllegalStateException,
                                java.lang.IllegalArgumentException
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.
servlet - The Servlet that is associated with this PageContextrequest - The currently pending request for this Servletresponse - The currently pending response for this ServleterrorPageURL - The value of the errorpage attribute from the page
     directive or nullneedsSession - The value of the session attribute from the
     page directivebufferSize - The value of the buffer attribute from the page
     directiveautoFlush - The value of the autoflush attribute from the page
     directivejava.io.IOException - during creation of JspWriterjava.lang.IllegalStateException - if out not correctly initializedjava.lang.IllegalArgumentException - If one of the given parameters
     is invalidpublic abstract void release()
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.
public abstract javax.servlet.http.HttpSession getSession()
public abstract java.lang.Object getPage()
public abstract javax.servlet.ServletRequest getRequest()
public abstract javax.servlet.ServletResponse getResponse()
public abstract java.lang.Exception getException()
public abstract javax.servlet.ServletConfig getServletConfig()
public abstract javax.servlet.ServletContext getServletContext()
public abstract void forward(java.lang.String relativeUrlPath)
                      throws javax.servlet.ServletException,
                             java.io.IOException
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.
 
relativeUrlPath - specifies the relative URL path to the target
     resource as described abovejava.lang.IllegalStateException - if  ServletResponse  is not
     in a state where a forward can be performedjavax.servlet.ServletException - if the page that was forwarded to throws
     a ServletExceptionjava.io.IOException - if an I/O error occurred while forwardingpublic abstract void include(java.lang.String relativeUrlPath)
                      throws javax.servlet.ServletException,
                             java.io.IOException
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.
 
relativeUrlPath - specifies the relative URL path to the target
     resource to be includedjavax.servlet.ServletException - if the page that was forwarded to throws
     a ServletExceptionjava.io.IOException - if an I/O error occurred while forwardingpublic abstract void include(java.lang.String relativeUrlPath,
           boolean flush)
                      throws javax.servlet.ServletException,
                             java.io.IOException
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.
 
relativeUrlPath - specifies the relative URL path to the
     target resource to be includedflush - True if the JspWriter is to be flushed before the include,
     or false if not.javax.servlet.ServletException - if the page that was forwarded to throws
     a ServletExceptionjava.io.IOException - if an I/O error occurred while forwardingpublic abstract void handlePageException(java.lang.Exception e)
                                  throws javax.servlet.ServletException,
                                         java.io.IOException
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 compatibility reasons. Newly generated code should use PageContext.handlePageException(Throwable).
e - the exception to be handledjavax.servlet.ServletException - if an error occurs while invoking the error pagejava.io.IOException - if an I/O error occurred while invoking the error
     pagejava.lang.NullPointerException - if the exception is nullhandlePageException(Throwable)public abstract void handlePageException(java.lang.Throwable t)
                                  throws javax.servlet.ServletException,
                                         java.io.IOException
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.
t - the throwable to be handledjavax.servlet.ServletException - if an error occurs while invoking the error pagejava.io.IOException - if an I/O error occurred while invoking the error
     pagejava.lang.NullPointerException - if the exception is nullhandlePageException(Exception)public BodyContent pushBody()
public ErrorData getErrorData()
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