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()
forwarding, inclusion
and error handlingforward()
include()
handlePageException()
static 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 String | CONFIG - Name used to store ServletConfig in PageContext name table.
|
static String | EXCEPTION - Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.
|
static String | OUT - Name used to store current JspWriter in PageContext name table.
|
static String | PAGE - Name used to store the Servlet in this PageContext's nametables.
|
static String | PAGECONTEXT - Name used to store this PageContext in it's own name table.
|
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 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 String | RESPONSE - Name used to store ServletResponse in PageContext name table.
|
static 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.
|
abstract Object | findAttribute(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(String relativeUrlPath) -
This method is used to re-direct, or "forward" the current ServletRequest and ServletResponse to another active component in the application.
|
abstract Object | getAttribute(String name) - Return the object associated with the name in the page scope or null
if not found.
|
abstract Object | getAttribute(String name, int scope) - Return the object associated with the name in the specified
scope or null if not found.
|
abstract Enumeration | getAttributeNamesInScope(int scope) - Enumerate all the attributes in a given scope
|
abstract int | getAttributesScope(String name) - Get the scope where a given attribute is defined.
|
abstract Exception | getException() - The current value of the exception object (an Exception).
|
abstract JspWriter | getOut() - The current value of the out object (a JspWriter).
|
abstract 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(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(Throwable t) -
This method is identical to the handlePageException(Exception),
except that it accepts a Throwable.
|
abstract void | include(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, 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(String name) - Remove the object reference associated with the given name,
look in all scopes in the scope order.
|
abstract void | removeAttribute(String name, int scope) - Remove the object reference associated with the specified name
in the given scope.
|
abstract void | setAttribute(String name, Object attribute) - Register the name and object specified with page scope semantics.
|
abstract void | setAttribute(String name, Object o, int scope) - register the name and object specified with appropriate scope semantics
|
APPLICATION
public static final String APPLICATION
Name used to store ServletContext in PageContext name table.
APPLICATION_SCOPE
public static final int APPLICATION_SCOPE
Application scope: named reference remains available in the
ServletContext until it is reclaimed.
CONFIG
public static final String CONFIG
Name used to store ServletConfig in PageContext name table.
EXCEPTION
public static final String EXCEPTION
Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.
OUT
public static final String OUT
Name used to store current JspWriter in PageContext name table.
PAGE
public static final String PAGE
Name used to store the Servlet in this PageContext's nametables.
PAGECONTEXT
public static final String PAGECONTEXT
Name used to store this PageContext in it's own name table.
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
public static final String REQUEST
Name used to store ServletRequest in PageContext name table.
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.
RESPONSE
public static final String RESPONSE
Name used to store ServletResponse in PageContext name table.
SESSION
public static final String SESSION
Name used to store HttpSession in PageContext name table.
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.
findAttribute
public abstract Object findAttribute(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.
- the value associated or null
forward
public abstract 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.
relativeUrlPath
- specifies the relative URL path to the target resource as described above
getAttribute
public abstract Object getAttribute(String name)
Return the object associated with the name in the page scope or null
if not found.
name
- the name of the attribute to get
getAttribute
public abstract Object getAttribute(String name,
int scope)
Return the object associated with the name in the specified
scope or null if not found.
name
- the name of the attribute to setscope
- the scope with which to associate the name/object
getAttributeNamesInScope
public abstract Enumeration getAttributeNamesInScope(int scope)
Enumerate all the attributes in a given scope
- an enumeration of names (java.lang.String) of all the attributes the specified scope
getAttributesScope
public abstract int getAttributesScope(String name)
Get the scope where a given attribute is defined.
- the scope of the object associated with the name specified or 0
getException
public abstract Exception getException()
The current value of the exception object (an Exception).
- any exception passed to this as an errorpage
getOut
public abstract JspWriter getOut()
The current value of the out object (a JspWriter).
- the current JspWriter stream being used for client response
getPage
public abstract Object getPage()
The current value of the page object (a Servlet).
- the Page implementation class instance (Servlet) associated with this PageContext
getRequest
public abstract ServletRequest getRequest()
The current value of the request object (a ServletRequest).
- The ServletRequest for this PageContext
getResponse
public abstract ServletResponse getResponse()
The current value of the response object (a ServletResponse).
- the ServletResponse for this PageContext
getServletConfig
public abstract ServletConfig getServletConfig()
The ServletConfig instance.
- the ServletConfig for this PageContext
getServletContext
public abstract ServletContext getServletContext()
The ServletContext instance.
- the ServletContext for this PageContext
getSession
public abstract HttpSession getSession()
The current value of the session object (an HttpSession).
- the HttpSession for this PageContext or null
handlePageException
public abstract void handlePageException(Exception e)
throws ServletException,
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).
e
- the exception to be handled
handlePageException
public abstract void handlePageException(Throwable t)
throws ServletException,
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.
t
- the throwable to be handled
include
public abstract 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.
relativeUrlPath
- specifies the relative URL path to the target resource to be included
initialize
public abstract 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.
servlet
- The Servlet that is associated with this PageContextrequest
- The currently pending request for this Servletresponse
- The currently pending response for this ServleterrorPageURL
- The value of the errorpage attribute from the page directive or nullneedsSession
- The value of the session attribute from the page directivebufferSize
- The value of the buffer attribute from the page directiveautoFlush
- The value of the autoflush attribute from the page directive
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
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
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.
removeAttribute
public abstract void removeAttribute(String name)
Remove the object reference associated with the given name,
look in all scopes in the scope order.
name
- The name of the object to remove.
removeAttribute
public abstract void removeAttribute(String name,
int scope)
Remove the object reference associated with the specified name
in the given scope.
name
- The name of the object to remove.scope
- The scope where to look.
setAttribute
public abstract void setAttribute(String name,
Object attribute)
Register the name and object specified with page scope semantics.
name
- the name of the attribute to setattribute
- the object to associate with the name
setAttribute
public abstract void setAttribute(String name,
Object o,
int scope)
register the name and object specified with appropriate scope semantics
name
- the name of the attribute to seto
- the object to associate with the namescope
- the scope with which to associate the name/object