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javax.servlet.jsp
abstract public class: PageContext [javadoc | source]

java.lang.Object
   javax.servlet.jsp.JspContext
      javax.servlet.jsp.PageContext

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().

Field 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.

Constructor:
public PageContext() { } Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method from javax.servlet.jsp.PageContext Summary:
forward,   getErrorData,   getException,   getPage,   getRequest,   getResponse,   getServletConfig,   getServletContext,   getSession,   handlePageException,   handlePageException,   include,   include,   initialize,   pushBody,   release

Methods from javax.servlet.jsp.JspContext:
findAttribute,   getAttribute,   getAttribute,   getAttributeNamesInScope,   getAttributesScope,   getELContext,   getExpressionEvaluator,   getOut,   getVariableResolver,   popBody,   pushBody,   removeAttribute,   removeAttribute,   setAttribute,   setAttribute

Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait

Method from javax.servlet.jsp.PageContext Detail:
abstract public void forward(String relativeUrlPath) throws ServletException, 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.
public ErrorData getErrorData() { 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" ) ); } Provides convenient access to error information.
abstract public Exception getException() The current value of the exception object (an Exception).
abstract public Object getPage() The current value of the page object (In a Servlet environment, this is an instance of javax.servlet.Servlet).
abstract public ServletRequest getRequest() The current value of the request object (a ServletRequest).
abstract public ServletResponse getResponse() The current value of the response object (a ServletResponse).
abstract public ServletConfig getServletConfig() The ServletConfig instance.
abstract public ServletContext getServletContext() The ServletContext instance.
abstract public HttpSession getSession() The current value of the session object (an HttpSession).
abstract public void handlePageException(Exception e) throws ServletException, 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 compatiblity reasons. Newly generated code should use PageContext.handlePageException(Throwable).
abstract public void handlePageException(Throwable t) throws ServletException, 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.
abstract public void include(String relativeUrlPath) throws ServletException, 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.
abstract public void include(String relativeUrlPath, boolean flush) throws ServletException, 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.
abstract public void initialize(Servlet servlet, ServletRequest request, ServletResponse response, String errorPageURL, boolean needsSession, int bufferSize, boolean autoFlush) throws IOException, IllegalStateException, 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.
public BodyContent pushBody() { return null; // XXX to implement } 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 public 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.