javax.servlet.jsp
Class PageContext

java.lang.Object
  |
  +--javax.servlet.jsp.PageContext

public abstract class PageContext

extends java.lang.Object

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.

An instance of an implementation dependent subclass of this abstract base class is created by a JSP implementation class at the begining of it's _jspService() method via an implementation default JspFactory , as follows:

 public class foo implements Servlet {

 // ...

public void _jspService(HttpServletRequest request,
			HttpServletResponse response)
       throws IOException, ServletException {

    JspFactory  factory     = JspFactory.getDefaultFactory();
    PageContext pageContext = factory.getPageContext(
this,
request,
response,
null,  // errorPageURL
false, // needsSession
JspWriter.DEFAULT_BUFFER,
true   // autoFlush
);

    // initialize implicit variables for scripting env ...

    HttpSession session = pageContext.getSession();
    JspWriter   out     = pageContext.getOut();
    Object      page    = this;

    try {
        // body of translated JSP here ...
    } catch (Exception e) {
        out.clear();
        pageContext.handlePageException(e);
    } finally {
        out.close();
	  factory.releasePageContext(pageContext);
    }
}

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().

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

Field Summary

static java.lang.String	APPLICATION name used to store ServletContext in PageContext name table
static int	APPLICATION_SCOPE application scope: named reference remains available in the ServletContext until it is reclaimed.
static java.lang.String	CONFIG name used to store ServletConfig in PageContext name table
static java.lang.String	EXCEPTION name used to store uncaught exception in ServletRequest attribute list and PageContext name table
static java.lang.String	OUT name used to store current JspWriter in PageContext name table
static java.lang.String	PAGE name used to store the Servlet in this PageContext's nametables
static 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.
static java.lang.String	PAGECONTEXT name used to store this PageContext in it's own name tables
static java.lang.String	REQUEST name used to store ServletRequest in PageContext name table
static int	REQUEST_SCOPE request scope: the named reference remains available from the ServletRequest associated with the Servlet that until the current request is completed.
static java.lang.String	RESPONSE name used to store ServletResponse in PageContext name table
static java.lang.String	SESSION name used to store HttpSession in PageContext name table
static 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.

Constructor Summary

PageContext()

Method Summary

abstract java.lang.Object	findAttribute(java.lang.String name) Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and returns the value associated or null.
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.
abstract java.lang.Object	getAttribute(java.lang.String name) return the object associated with the name in the page scope or null
abstract java.lang.Object	getAttribute(java.lang.String name, int scope) return the object associated with the name in the specifed scope or null
abstract java.util.Enumeration	getAttributeNamesInScope(int scope)
abstract int	getAttributesScope(java.lang.String name)
abstract java.lang.Exception	getException()
abstract JspWriter	getOut()
abstract java.lang.Object	getPage()
abstract ServletRequest	getRequest()
abstract ServletResponse	getResponse()
abstract ServletConfig	getServletConfig()
abstract ServletContext	getServletContext()
abstract HttpSession	getSession()
abstract void	handlePageException(java.lang.Exception e) 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.
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	initialize(Servlet servlet, ServletRequest request, ServletResponse response, java.lang.String errorPageURL, boolean needsSession, int bufferSize, boolean autoFlush) The initialize emthod 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 wihtin it's _jspService() method.
JspWriter	popBody() Return the previous JspWriter "out" saved by the matching pushBody(), and update the value of the "out" attribute in the page scope attribute namespace of the PageConxtext
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().
abstract void	removeAttribute(java.lang.String name) remove the object reference associated with the specified name
abstract void	removeAttribute(java.lang.String name, int scope) remove the object reference associated with the specified name
abstract void	setAttribute(java.lang.String name, java.lang.Object attribute) register the name and object specified with page scope semantics
abstract void	setAttribute(java.lang.String name, java.lang.Object o, int scope) register the name and object specified with appropriate scope semantics

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

PAGE_SCOPE

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.

REQUEST_SCOPE

public static final int REQUEST_SCOPE

request scope: the named reference remains available from the ServletRequest associated with the Servlet that until the current request is completed.

SESSION_SCOPE

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.

APPLICATION_SCOPE

public static final int APPLICATION_SCOPE

application scope: named reference remains available in the ServletContext until it is reclaimed.

PAGE

public static final java.lang.String PAGE

name used to store the Servlet in this PageContext's nametables

PAGECONTEXT

public static final java.lang.String PAGECONTEXT

name used to store this PageContext in it's own name tables

REQUEST

public static final java.lang.String REQUEST

name used to store ServletRequest in PageContext name table

RESPONSE

public static final java.lang.String RESPONSE

name used to store ServletResponse in PageContext name table

CONFIG

public static final java.lang.String CONFIG

name used to store ServletConfig in PageContext name table

SESSION

public static final java.lang.String SESSION

name used to store HttpSession in PageContext name table

OUT

public static final java.lang.String OUT

name used to store current JspWriter in PageContext name table

APPLICATION

public static final java.lang.String APPLICATION

name used to store ServletContext in PageContext name table

EXCEPTION

public static final java.lang.String EXCEPTION

name used to store uncaught exception in ServletRequest attribute list and PageContext name table

Constructor Detail

PageContext

public PageContext()

Method Detail

initialize

public abstract void initialize(Servlet servlet,
                                ServletRequest request,
                                ServletResponse response,
                                java.lang.String errorPageURL,
                                boolean needsSession,
                                int bufferSize,
                                boolean autoFlush)
                         throws java.io.IOException,
                                java.lang.IllegalStateException,
                                java.lang.IllegalArgumentException

The initialize emthod 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 wihtin 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.

Parameters:

servlet - The Servlet that is associated with this PageContext

request - The currently pending request for this Servlet

response - The currently pending response for this Servlet

errorPageURL - The value of the errorpage attribute from the page directive or null

needsSession - The value of the session attribute from the page directive

bufferSize - The value of the buffer attribute from the page directive

autoFlush - The value of the autoflush attribute from the page directive

Throws:

java.io.IOException - during creation of JspWriter

java.lang.IllegalStateException - if out not correctly initialized

release

public 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

setAttribute

public abstract void setAttribute(java.lang.String name,
                                  java.lang.Object attribute)

register the name and object specified with page scope semantics

Throws:

NullPointerException - if the name or object is null

setAttribute

public abstract void setAttribute(java.lang.String name,
                                  java.lang.Object o,
                                  int scope)

register the name and object specified with appropriate scope semantics

Parameters:

name - the name of the attribute to set

o - the object to associate with the name

scope - the scope with which to associate the name/object

Throws:

NullPointerException - if the name or object is null

java.lang.IllegalArgumentException - if the scope is invalid

getAttribute

public abstract java.lang.Object getAttribute(java.lang.String name)

return the object associated with the name in the page scope or null

Parameters:

name - the name of the attribute to get

Throws:

NullPointerException - if the name is null

java.lang.IllegalArgumentException - if the scope is invalid

getAttribute

public abstract java.lang.Object getAttribute(java.lang.String name,
                                              int scope)

return the object associated with the name in the specifed scope or null

Parameters:

name - the name of the attribute to set

scope - the scope with which to associate the name/object

Throws:

NullPointerException - if the name is null

java.lang.IllegalArgumentException - if the scope is invalid

findAttribute

public abstract java.lang.Object findAttribute(java.lang.String name)

Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and returns the value associated or null.

Returns:

the value associated or null

removeAttribute

public abstract void removeAttribute(java.lang.String name)

remove the object reference associated with the specified name

removeAttribute

public abstract void removeAttribute(java.lang.String name,
                                     int scope)

remove the object reference associated with the specified name

getAttributesScope

public abstract int getAttributesScope(java.lang.String name)

Returns:

the scope of the object associated with the name specified or 0

getAttributeNamesInScope

public abstract java.util.Enumeration getAttributeNamesInScope(int scope)

Returns:

an enumeration of names (java.lang.String) of all the attributes the specified scope

getOut

public abstract JspWriter getOut()

Returns:

the current JspWriter stream being used for client response

getSession

public abstract HttpSession getSession()

Returns:

the HttpSession for this PageContext or null

getPage

public abstract java.lang.Object getPage()

Returns:

the Page implementation class instance (Servlet) associated with this PageContext

getRequest

public abstract ServletRequest getRequest()

Returns:

The ServletRequest for this PageContext

getResponse

public abstract ServletResponse getResponse()

Returns:

the ServletResponse for this PageContext

getException

public abstract java.lang.Exception getException()

Returns:

any exception passed to this as an errorpage

getServletConfig

public abstract ServletConfig getServletConfig()

Returns:

the ServletConfig for this PageContext

getServletContext

public abstract ServletContext getServletContext()

Returns:

the ServletContext for this PageContext

forward

public abstract void forward(java.lang.String relativeUrlPath)
                      throws 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.

Parameters:

relativeUrlPath - specifies the relative URL path to the target resource as described above

Throws:

ServletException -

java.io.IOException -

java.lang.IllegalArgumentException - if target resource URL is unresolvable

java.lang.IllegalStateException - if ServletResponse is not in a state where a forward can be performed

java.lang.SecurityException - if target resource cannot be accessed by caller

include

public abstract void include(java.lang.String relativeUrlPath)
                      throws 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.

Parameters:

relativeUrlPath - specifies the relative URL path to the target resource to be included

Throws:

ServletException -

java.io.IOException -

java.lang.IllegalArgumentException - if the target resource URL is unresolvable

java.lang.SecurityException - if target resource cannot be accessed by caller

handlePageException

public abstract void handlePageException(java.lang.Exception e)
                                  throws ServletException,
                                         java.io.IOException

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.

Parameters:

e - the exception to be handled

Throws:

ServletException -

java.io.IOException -

NullPointerException - if the exception is null

java.lang.SecurityException - if target resource cannot be accessed by caller

pushBody

public 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

Returns:

the new BodyContent

popBody

public JspWriter popBody()

Return the previous JspWriter "out" saved by the matching pushBody(), and update the value of the "out" attribute in the page scope attribute namespace of the PageConxtext

Returns:

the saved JspWriter.