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. Implicit objects are added 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() and popBody()

Methods Intended for JSP authors

Some methods provide uniform access to the diverse objects representing scopes. The implementation must use the underlying Servlet machinery corresponding to that scope, so information can be passed back and forth between Servlets and JSP pages. The methods are: setAttribute(), getAttribute(), findAttribute(), removeAttribute(), getAttributesScope() and getAttributeNamesInScope() .

The following methods provide convenient access to implicit objects:

getOut(), 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

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 table.
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 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 if not found.
abstract java.lang.Object	getAttribute(java.lang.String name, int scope) Return the object associated with the name in the specified scope or null if not found.
abstract java.util.Enumeration	getAttributeNamesInScope(int scope) Enumerate all the attributes in a given scope
abstract int	getAttributesScope(java.lang.String name) Get the scope where a given attribute is defined.
abstract java.lang.Exception	getException() The current value of the exception object (an Exception).
abstract JspWriter	getOut() The current value of the out object (a JspWriter).
abstract java.lang.Object	getPage() The current value of the page object (a Servlet).
abstract ServletRequest	getRequest() The current value of the request object (a ServletRequest).
abstract ServletResponse	getResponse() The current value of the response object (a ServletResponse).
abstract ServletConfig	getServletConfig() The ServletConfig instance.
abstract ServletContext	getServletContext() The ServletContext instance.
abstract 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 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	handlePageException(java.lang.Throwable t) This method is identical to the handlePageException(Exception), except that it accepts a Throwable.
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 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.
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 given name, look in all scopes in the scope order.
abstract void	removeAttribute(java.lang.String name, int scope) Remove the object reference associated with the specified name in the given scope.
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.

See Also:

Constant Field Values

REQUEST_SCOPE

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.

See Also:

Constant Field Values

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.

See Also:

Constant Field Values

APPLICATION_SCOPE

public static final int APPLICATION_SCOPE

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

See Also:

Constant Field Values

PAGE

public static final java.lang.String PAGE

Name used to store the Servlet in this PageContext's nametables.

See Also:

Constant Field Values

PAGECONTEXT

public static final java.lang.String PAGECONTEXT

Name used to store this PageContext in it's own name table.

See Also:

Constant Field Values

REQUEST

public static final java.lang.String REQUEST

Name used to store ServletRequest in PageContext name table.

See Also:

Constant Field Values

RESPONSE

public static final java.lang.String RESPONSE

Name used to store ServletResponse in PageContext name table.

See Also:

Constant Field Values

CONFIG

public static final java.lang.String CONFIG

Name used to store ServletConfig in PageContext name table.

See Also:

Constant Field Values

SESSION

public static final java.lang.String SESSION

Name used to store HttpSession in PageContext name table.

See Also:

Constant Field Values

OUT

public static final java.lang.String OUT

Name used to store current JspWriter in PageContext name table.

See Also:

Constant Field Values

APPLICATION

public static final java.lang.String APPLICATION

Name used to store ServletContext in PageContext name table.

See Also:

Constant Field Values

EXCEPTION

public static final java.lang.String EXCEPTION

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

See Also:

Constant Field Values

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 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.

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

java.lang.IllegalArgumentException

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.

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

setAttribute

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

Register the name and object specified with page scope semantics.

Parameters:

name - the name of the attribute to set

attribute - the object to associate with the name

Throws:

java.lang.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:

java.lang.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 if not found.

Parameters:

name - the name of the attribute to get

Throws:

java.lang.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 specified scope or null if not found.

Parameters:

name - the name of the attribute to set

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

Throws:

java.lang.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 given name, look in all scopes in the scope order.

Parameters:

name - The name of the object to remove.

removeAttribute

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

Remove the object reference associated with the specified name in the given scope.

Parameters:

name - The name of the object to remove.

scope - The scope where to look.

getAttributesScope

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

Get the scope where a given attribute is defined.

Returns:

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

getAttributeNamesInScope

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

Enumerate all the attributes in a given scope

Returns:

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

getOut

public abstract JspWriter getOut()

The current value of the out object (a JspWriter).

Returns:

the current JspWriter stream being used for client response

getSession

public abstract HttpSession getSession()

The current value of the session object (an HttpSession).

Returns:

the HttpSession for this PageContext or null

getPage

public abstract java.lang.Object getPage()

The current value of the page object (a Servlet).

Returns:

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

getRequest

public abstract ServletRequest getRequest()

The current value of the request object (a ServletRequest).

Returns:

The ServletRequest for this PageContext

getResponse

public abstract ServletResponse getResponse()

The current value of the response object (a ServletResponse).

Returns:

the ServletResponse for this PageContext

getException

public abstract java.lang.Exception getException()

The current value of the exception object (an Exception).

Returns:

any exception passed to this as an errorpage

getServletConfig

public abstract ServletConfig getServletConfig()

The ServletConfig instance.

Returns:

the ServletConfig for this PageContext

getServletContext

public abstract ServletContext getServletContext()

The ServletContext instance.

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.

This method is kept for backwards compatiblity reasons. Newly generated code should use PageContext.handlePageException(Throwable).

Parameters:

e - the exception to be handled

Throws:

ServletException

java.io.IOException

java.lang.NullPointerException - if the exception is null

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

See Also:

handlePageException(Throwable)

handlePageException

public abstract void handlePageException(java.lang.Throwable t)
                                  throws ServletException,
                                         java.io.IOException

This method is identical to the handlePageException(Exception), except that it accepts a Throwable. This is the preferred method to use as it allows proper implementation of the errorpage semantics.

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:

t - the throwable to be handled

Throws:

ServletException

java.io.IOException

java.lang.NullPointerException - if the exception is null

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

See Also:

handlePageException(Exception)

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.