Class 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:
- 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()
and getServletContext()
.
The following methods provide support for forwarding, inclusion
and error handling:
forward()
, include()
,
and handlePageException()
.
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final String
Name used to store ServletContext in PageContext name table.static final int
Application scope: named reference remains available in the ServletContext until it is reclaimed.static final String
Name used to store ServletConfig in PageContext name table.static final String
Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.static final String
Name used to store current JspWriter in PageContext name table.static final String
Name used to store the Servlet in this PageContext's nametables.static final int
Page scope: (this is the default) the named reference remains available in this PageContext until the return from the current Servlet.service() invocation.static final String
Name used to store this PageContext in it's own name table.static final String
Name used to store ServletRequest in PageContext name table.static final int
Request scope: the named reference remains available from the ServletRequest associated with the Servlet until the current request is completed.static final String
Name used to store ServletResponse in PageContext name table.static final String
Name used to store HttpSession in PageContext name table.static final int
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
Constructors -
Method Summary
Modifier and TypeMethodDescriptionabstract 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
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 scopeabstract int
getAttributesScope
(String name) Get the scope where a given attribute is defined.abstract Exception
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
The current value of the request object (a ServletRequest).abstract ServletResponse
The current value of the response object (a ServletResponse).abstract ServletConfig
The ServletConfig instance.abstract ServletContext
The ServletContext instance.abstract HttpSession
The current value of the session object (an HttpSession).abstract void
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
This method is identical to the handlePageException(Exception), except that it accepts a Throwable.abstract void
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.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 PageConxtextpushBody()
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 PageContextabstract 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
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Field Details
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PAGE_SCOPE
public static final int PAGE_SCOPEPage scope: (this is the default) the named reference remains available in this PageContext until the return from the current Servlet.service() invocation.- See Also:
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REQUEST_SCOPE
public static final int REQUEST_SCOPERequest scope: the named reference remains available from the ServletRequest associated with the Servlet until the current request is completed.- See Also:
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SESSION_SCOPE
public static final int SESSION_SCOPESession 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:
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APPLICATION_SCOPE
public static final int APPLICATION_SCOPEApplication scope: named reference remains available in the ServletContext until it is reclaimed.- See Also:
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PAGE
Name used to store the Servlet in this PageContext's nametables.- See Also:
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PAGECONTEXT
Name used to store this PageContext in it's own name table.- See Also:
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REQUEST
Name used to store ServletRequest in PageContext name table.- See Also:
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RESPONSE
Name used to store ServletResponse in PageContext name table.- See Also:
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CONFIG
Name used to store ServletConfig in PageContext name table.- See Also:
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SESSION
Name used to store HttpSession in PageContext name table.- See Also:
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OUT
Name used to store current JspWriter in PageContext name table.- See Also:
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APPLICATION
Name used to store ServletContext in PageContext name table.- See Also:
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EXCEPTION
Name used to store uncaught exception in ServletRequest attribute list and PageContext name table.- See Also:
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Constructor Details
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PageContext
public PageContext()
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Method Details
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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.
- Parameters:
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- Throws:
IOException
- during creation of JspWriterIllegalStateException
- if out not correctly initializedIllegalArgumentException
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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.
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setAttribute
Register the name and object specified with page scope semantics.- Parameters:
name
- the name of the attribute to setattribute
- the object to associate with the name- Throws:
NullPointerException
- if the name or object is null
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setAttribute
register the name and object specified with appropriate scope semantics- Parameters:
name
- the name of the attribute to seto
- the object to associate with the namescope
- the scope with which to associate the name/object- Throws:
NullPointerException
- if the name or object is nullIllegalArgumentException
- if the scope is invalid
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getAttribute
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:
NullPointerException
- if the name is nullIllegalArgumentException
- if the scope is invalid
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getAttribute
Return the object associated with the name in the specified scope or null if not found.- Parameters:
name
- the name of the attribute to setscope
- the scope with which to associate the name/object- Throws:
NullPointerException
- if the name is nullIllegalArgumentException
- if the scope is invalid
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findAttribute
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
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removeAttribute
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.
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removeAttribute
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.
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getAttributesScope
Get the scope where a given attribute is defined.- Returns:
- the scope of the object associated with the name specified or 0
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getAttributeNamesInScope
Enumerate all the attributes in a given scope- Returns:
- an enumeration of names (java.lang.String) of all the attributes the specified scope
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getOut
The current value of the out object (a JspWriter).- Returns:
- the current JspWriter stream being used for client response
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getSession
The current value of the session object (an HttpSession).- Returns:
- the HttpSession for this PageContext or null
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getPage
The current value of the page object (a Servlet).- Returns:
- the Page implementation class instance (Servlet) associated with this PageContext
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getRequest
The current value of the request object (a ServletRequest).- Returns:
- The ServletRequest for this PageContext
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getResponse
The current value of the response object (a ServletResponse).- Returns:
- the ServletResponse for this PageContext
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getException
The current value of the exception object (an Exception).- Returns:
- any exception passed to this as an errorpage
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getServletConfig
The ServletConfig instance.- Returns:
- the ServletConfig for this PageContext
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getServletContext
The ServletContext instance.- Returns:
- the ServletContext for this PageContext
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forward
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 theServletResponse
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
IOException
IllegalArgumentException
- if target resource URL is unresolvableIllegalStateException
- ifServletResponse
is not in a state where a forward can be performedSecurityException
- if target resource cannot be accessed by caller
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include
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:
ServletException
IOException
IllegalArgumentException
- if the target resource URL is unresolvableSecurityException
- if target resource cannot be accessed by caller
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handlePageException
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
IOException
NullPointerException
- if the exception is nullSecurityException
- if target resource cannot be accessed by caller- See Also:
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handlePageException
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.
- Parameters:
t
- the throwable to be handled- Throws:
ServletException
IOException
NullPointerException
- if the exception is nullSecurityException
- if target resource cannot be accessed by caller- See Also:
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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
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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.
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