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
|
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 tables
|
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 that 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
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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.
|
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.
|
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.
|
Object | getAttribute(String name) - return the object associated with the name in the page scope or null
|
Object | getAttribute(String name, int scope) - return the object associated with the name in the specifed scope or null
|
Enumeration | getAttributeNamesInScope(int scope)
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int | getAttributesScope(String name)
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Exception | getException()
|
JspWriter | getOut()
|
Object | getPage()
|
ServletRequest | getRequest()
|
ServletResponse | getResponse()
|
ServletConfig | getServletConfig()
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ServletContext | getServletContext()
|
HttpSession | getSession()
|
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.
|
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.
|
void | initialize(Servlet servlet, ServletRequest request, ServletResponse response, 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
|
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().
|
void | removeAttribute(String name) - remove the object reference associated with the specified name
|
void | removeAttribute(String name, int scope) - remove the object reference associated with the specified name
|
void | setAttribute(String name, Object attribute) - register the name and object specified with page scope semantics
|
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.
- 4
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 tables
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.
- 1
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 that until the current request is completed.
- 2
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.
- 3
findAttribute
public 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 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
ServletException
-
getAttribute
public Object getAttribute(String name)
return the object associated with the name in the page scope or null
name
- the name of the attribute to get
getAttribute
public Object getAttribute(String name,
int scope)
return the object associated with the name in the specifed scope or null
name
- the name of the attribute to setscope
- the scope with which to associate the name/object
getAttributeNamesInScope
public Enumeration getAttributeNamesInScope(int scope)
- an enumeration of names (java.lang.String) of all the attributes the specified scope
getAttributesScope
public int getAttributesScope(String name)
- the scope of the object associated with the name specified or 0
getException
public Exception getException()
- any exception passed to this as an errorpage
getOut
public JspWriter getOut()
- the current JspWriter stream being used for client response
getPage
public Object getPage()
- the Page implementation class instance (Servlet) associated with this PageContext
getRequest
public ServletRequest getRequest()
- The ServletRequest for this PageContext
getResponse
public ServletResponse getResponse()
- the ServletResponse for this PageContext
getServletConfig
public ServletConfig getServletConfig()
- the ServletConfig for this PageContext
getServletContext
public ServletContext getServletContext()
- the ServletContext for this PageContext
getSession
public HttpSession getSession()
- the HttpSession for this PageContext or null
handlePageException
public 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.
e
- the exception to be handled
ServletException
-
include
public 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
ServletException
-
initialize
public void initialize(Servlet servlet,
ServletRequest request,
ServletResponse response,
String errorPageURL,
boolean needsSession,
int bufferSize,
boolean autoFlush)
throws IOException,
IllegalStateException,
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.
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
- the saved JspWriter.
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
- the new BodyContent
release
public 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
removeAttribute
public void removeAttribute(String name)
remove the object reference associated with the specified name
removeAttribute
public void removeAttribute(String name,
int scope)
remove the object reference associated with the specified name
setAttribute
public void setAttribute(String name,
Object attribute)
register the name and object specified with page scope semantics
setAttribute
public 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
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