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java.lang.Object | +--javax.servlet.jsp.PageContext
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:
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 |
public static final int PAGE_SCOPE
public static final int REQUEST_SCOPE
public static final int SESSION_SCOPE
public static final int APPLICATION_SCOPE
public static final java.lang.String PAGE
public static final java.lang.String PAGECONTEXT
public static final java.lang.String REQUEST
public static final java.lang.String RESPONSE
public static final java.lang.String CONFIG
public static final java.lang.String SESSION
public static final java.lang.String OUT
public static final java.lang.String APPLICATION
public static final java.lang.String EXCEPTION
Constructor Detail |
public PageContext()
Method Detail |
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.
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
java.io.IOException
- during creation of JspWriter
java.lang.IllegalStateException
- if out not correctly initialized
java.lang.IllegalArgumentException
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.
public abstract void setAttribute(java.lang.String name, java.lang.Object attribute)
name
- the name of the attribute to setattribute
- the object to associate with the name
java.lang.NullPointerException
- if the name or object is nullpublic abstract void setAttribute(java.lang.String name, java.lang.Object o, int scope)
name
- the name of the attribute to seto
- the object to associate with the namescope
- the scope with which to associate the name/object
java.lang.NullPointerException
- if the name or object is null
java.lang.IllegalArgumentException
- if the scope is invalidpublic abstract java.lang.Object getAttribute(java.lang.String name)
name
- the name of the attribute to get
java.lang.NullPointerException
- if the name is null
java.lang.IllegalArgumentException
- if the scope is invalidpublic abstract java.lang.Object getAttribute(java.lang.String name, int scope)
name
- the name of the attribute to setscope
- the scope with which to associate the name/object
java.lang.NullPointerException
- if the name is null
java.lang.IllegalArgumentException
- if the scope is invalidpublic abstract java.lang.Object findAttribute(java.lang.String name)
public abstract void removeAttribute(java.lang.String name)
name
- The name of the object to remove.public abstract void removeAttribute(java.lang.String name, int scope)
name
- The name of the object to remove.scope
- The scope where to look.public abstract int getAttributesScope(java.lang.String name)
public abstract java.util.Enumeration getAttributeNamesInScope(int scope)
public abstract JspWriter getOut()
public abstract HttpSession getSession()
public abstract java.lang.Object getPage()
public abstract ServletRequest getRequest()
public abstract ServletResponse getResponse()
public abstract java.lang.Exception getException()
public abstract ServletConfig getServletConfig()
public abstract ServletContext getServletContext()
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.
relativeUrlPath
- specifies the relative URL path to the target resource as described above
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 callerpublic 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.
relativeUrlPath
- specifies the relative URL path to the target resource to be included
ServletException
java.io.IOException
java.lang.IllegalArgumentException
- if the target resource URL is unresolvable
java.lang.SecurityException
- if target resource cannot be accessed by callerpublic 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).
e
- the exception to be handled
ServletException
java.io.IOException
java.lang.NullPointerException
- if the exception is null
java.lang.SecurityException
- if target resource cannot be accessed by callerhandlePageException(Throwable)
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.
t
- the throwable to be handled
ServletException
java.io.IOException
java.lang.NullPointerException
- if the exception is null
java.lang.SecurityException
- if target resource cannot be accessed by callerhandlePageException(Exception)
public BodyContent pushBody()
public JspWriter popBody()
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