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PageContext (Servlet and JavaServer Pages API Documentation)

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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()

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)

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)

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.

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.

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.

Overview

Package

Class

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Help

PREV CLASS NEXT CLASS

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SUMMARY: NESTED | FIELD | CONSTR | METHOD

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javax.servlet.jsp Class PageContext

PAGE_SCOPE

REQUEST_SCOPE

SESSION_SCOPE

APPLICATION_SCOPE

PAGE

PAGECONTEXT

REQUEST

RESPONSE

CONFIG

SESSION

OUT

APPLICATION

EXCEPTION

PageContext

initialize

release

setAttribute

setAttribute

getAttribute

getAttribute

findAttribute

removeAttribute

removeAttribute

getAttributesScope

getAttributeNamesInScope

getOut

getSession

getPage

getRequest

getResponse

getException

getServletConfig

getServletContext

forward

include

handlePageException

handlePageException

pushBody

popBody

javax.servlet.jsp
Class PageContext