Class PageContext
- java.lang.Object
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- javax.servlet.jsp.PageContext
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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()
andrelease()
The following methods enable the management of nested JspWriter streams to implement Tag Extensions:
pushBody()
andpopBody()
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()
andgetAttributeNamesInScope()
.The following methods provide convenient access to implicit objects:
getOut()
,getException()
,getPage()
getRequest()
,getResponse()
,getSession()
,getServletConfig()
andgetServletContext()
.The following methods provide support for forwarding, inclusion and error handling:
forward()
,include()
, andhandlePageException()
.
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Field Summary
Fields Modifier and Type Field Description 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.
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Constructor Summary
Constructors Constructor Description PageContext()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description 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 scopeabstract 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 PageConxtextBodyContent
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 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(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
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Field Detail
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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
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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
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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
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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
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PAGE
public static final java.lang.String PAGE
Name used to store the Servlet in this PageContext's nametables.- See Also:
- Constant Field Values
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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
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REQUEST
public static final java.lang.String REQUEST
Name used to store ServletRequest in PageContext name table.- See Also:
- Constant Field Values
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RESPONSE
public static final java.lang.String RESPONSE
Name used to store ServletResponse in PageContext name table.- See Also:
- Constant Field Values
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CONFIG
public static final java.lang.String CONFIG
Name used to store ServletConfig in PageContext name table.- See Also:
- Constant Field Values
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SESSION
public static final java.lang.String SESSION
Name used to store HttpSession in PageContext name table.- See Also:
- Constant Field Values
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OUT
public static final java.lang.String OUT
Name used to store current JspWriter in PageContext name table.- See Also:
- Constant Field Values
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APPLICATION
public static final java.lang.String APPLICATION
Name used to store ServletContext in PageContext name table.- See Also:
- Constant Field Values
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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
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Method Detail
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initialize
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.
- 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:
java.io.IOException
- during creation of JspWriterjava.lang.IllegalStateException
- if out not correctly initializedjava.lang.IllegalArgumentException
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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
public abstract void setAttribute(java.lang.String name, java.lang.Object attribute)
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:
java.lang.NullPointerException
- if the name or object is null
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setAttribute
public abstract void setAttribute(java.lang.String name, java.lang.Object o, int scope)
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:
java.lang.NullPointerException
- if the name or object is nulljava.lang.IllegalArgumentException
- if the scope is invalid
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getAttribute
public 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.- Parameters:
name
- the name of the attribute to get- Throws:
java.lang.NullPointerException
- if the name is nulljava.lang.IllegalArgumentException
- if the scope is invalid
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getAttribute
public 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.- Parameters:
name
- the name of the attribute to setscope
- the scope with which to associate the name/object- Throws:
java.lang.NullPointerException
- if the name is nulljava.lang.IllegalArgumentException
- if the scope is invalid
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findAttribute
public 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.- Returns:
- the value associated or null
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removeAttribute
public abstract void removeAttribute(java.lang.String name)
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
public abstract void removeAttribute(java.lang.String name, int scope)
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
public abstract int getAttributesScope(java.lang.String name)
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
public abstract java.util.Enumeration getAttributeNamesInScope(int scope)
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
public abstract JspWriter 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
public abstract HttpSession getSession()
The current value of the session object (an HttpSession).- Returns:
- the HttpSession for this PageContext or null
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getPage
public abstract java.lang.Object 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
public abstract ServletRequest getRequest()
The current value of the request object (a ServletRequest).- Returns:
- The ServletRequest for this PageContext
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getResponse
public abstract ServletResponse getResponse()
The current value of the response object (a ServletResponse).- Returns:
- the ServletResponse for this PageContext
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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
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getServletConfig
public abstract ServletConfig getServletConfig()
The ServletConfig instance.- Returns:
- the ServletConfig for this PageContext
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getServletContext
public abstract ServletContext getServletContext()
The ServletContext instance.- Returns:
- the ServletContext for this PageContext
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forward
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 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
java.io.IOException
java.lang.IllegalArgumentException
- if target resource URL is unresolvablejava.lang.IllegalStateException
- ifServletResponse
is not in a state where a forward can be performedjava.lang.SecurityException
- if target resource cannot be accessed by caller
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include
public 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.- Parameters:
relativeUrlPath
- specifies the relative URL path to the target resource to be included- Throws:
ServletException
java.io.IOException
java.lang.IllegalArgumentException
- if the target resource URL is unresolvablejava.lang.SecurityException
- if target resource cannot be accessed by caller
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handlePageException
public 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).
- Parameters:
e
- the exception to be handled- Throws:
ServletException
java.io.IOException
java.lang.NullPointerException
- if the exception is nulljava.lang.SecurityException
- if target resource cannot be accessed by caller- See Also:
handlePageException(Throwable)
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handlePageException
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.
- Parameters:
t
- the throwable to be handled- Throws:
ServletException
java.io.IOException
java.lang.NullPointerException
- if the exception is nulljava.lang.SecurityException
- if target resource cannot be accessed by caller- See Also:
handlePageException(Exception)
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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
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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- Returns:
- the saved JspWriter.
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