javax.servlet.jsp
Class PageContext

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

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().


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()
          Sole constructor.
 
Method Summary
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().
 
Methods inherited from class javax.servlet.jsp.JspContext
findAttribute, getAttribute, getAttribute, getAttributeNamesInScope, getAttributesScope, getELContext, getExpressionEvaluator, getOut, getVariableResolver, popBody, pushBody, removeAttribute, removeAttribute, setAttribute, setAttribute
 
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()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

initialize

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.

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 - If one of the given parameters is invalid

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.


getSession

public abstract javax.servlet.http.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 (In a Servlet environment, this is an instance of javax.servlet.Servlet).

Returns:
the Page implementation class instance associated with this PageContext

getRequest

public abstract javax.servlet.ServletRequest getRequest()
The current value of the request object (a ServletRequest).

Returns:
The ServletRequest for this PageContext

getResponse

public abstract javax.servlet.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 javax.servlet.ServletConfig getServletConfig()
The ServletConfig instance.

Returns:
the ServletConfig for this PageContext

getServletContext

public abstract javax.servlet.ServletContext getServletContext()
The ServletContext instance.

Returns:
the ServletContext for this PageContext

forward

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.

Parameters:
relativeUrlPath - specifies the relative URL path to the target resource as described above
Throws:
java.lang.IllegalStateException - if ServletResponse is not in a state where a forward can be performed
javax.servlet.ServletException - if the page that was forwarded to throws a ServletException
java.io.IOException - if an I/O error occurred while forwarding

include

public 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.

Parameters:
relativeUrlPath - specifies the relative URL path to the target resource to be included
Throws:
javax.servlet.ServletException - if the page that was forwarded to throws a ServletException
java.io.IOException - if an I/O error occurred while forwarding

include

public 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.

Parameters:
relativeUrlPath - specifies the relative URL path to the target resource to be included
flush - True if the JspWriter is to be flushed before the include, or false if not.
Throws:
javax.servlet.ServletException - if the page that was forwarded to throws a ServletException
java.io.IOException - if an I/O error occurred while forwarding
Since:
JSP 2.0

handlePageException

public 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 compatiblity reasons. Newly generated code should use PageContext.handlePageException(Throwable).

Parameters:
e - the exception to be handled
Throws:
javax.servlet.ServletException - if an error occurs while invoking the error page
java.io.IOException - if an I/O error occurred while invoking the error page
java.lang.NullPointerException - if the exception is null
See Also:
handlePageException(Throwable)

handlePageException

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.

Parameters:
t - the throwable to be handled
Throws:
javax.servlet.ServletException - if an error occurs while invoking the error page
java.io.IOException - if an I/O error occurred while invoking the error page
java.lang.NullPointerException - if the exception is null
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

getErrorData

public ErrorData getErrorData()
Provides convenient access to error information.

Returns:
an ErrorData instance containing information about the error, as obtained from the request attributes, as per the Servlet specification. If this is not an error page (that is, if the isErrorPage attribute of the page directive is not set to "true"), the information is meaningless.
Since:
JSP 2.0


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