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


    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 tables
    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 that 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
    abstract  java.lang.Object getAttribute(java.lang.String name, int scope)
              return the object associated with the name in the specifed scope or null
    abstract  java.util.Enumeration getAttributeNamesInScope(int scope)
               
    abstract  int getAttributesScope(java.lang.String name)
               
    abstract  java.lang.Exception getException()
               
    abstract  JspWriter getOut()
               
    abstract  java.lang.Object getPage()
               
    abstract  javax.servlet.ServletRequest getRequest()
               
    abstract  javax.servlet.ServletResponse getResponse()
               
    abstract  javax.servlet.ServletConfig getServletConfig()
               
    abstract  javax.servlet.ServletContext getServletContext()
               
    abstract  javax.servlet.http.HttpSession getSession()
               
    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 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(javax.servlet.Servlet servlet, javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, java.lang.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.
    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 specified name
    abstract  void removeAttribute(java.lang.String name, int scope)
              remove the object reference associated with the specified name
    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

    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_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.

    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.

    APPLICATION_SCOPE

    public static final int APPLICATION_SCOPE
    application scope: named reference remains available in the ServletContext until it is reclaimed.

    PAGE

    public static final java.lang.String PAGE
    name used to store the Servlet in this PageContext's nametables

    PAGECONTEXT

    public static final java.lang.String PAGECONTEXT
    name used to store this PageContext in it's own name tables

    REQUEST

    public static final java.lang.String REQUEST
    name used to store ServletRequest in PageContext name table

    RESPONSE

    public static final java.lang.String RESPONSE
    name used to store ServletResponse in PageContext name table

    CONFIG

    public static final java.lang.String CONFIG
    name used to store ServletConfig in PageContext name table

    SESSION

    public static final java.lang.String SESSION
    name used to store HttpSession in PageContext name table

    OUT

    public static final java.lang.String OUT
    name used to store current JspWriter in PageContext name table

    APPLICATION

    public static final java.lang.String APPLICATION
    name used to store ServletContext in PageContext name table

    EXCEPTION

    public static final java.lang.String EXCEPTION
    name used to store uncaught exception in ServletRequest attribute list and PageContext name table
    Constructor Detail

    PageContext

    public PageContext()
    Method Detail

    initialize

    public abstract void initialize(javax.servlet.Servlet servlet,
                                    javax.servlet.ServletRequest request,
                                    javax.servlet.ServletResponse response,
                                    java.lang.String errorPageURL,
                                    boolean needsSession,
                                    int bufferSize,
                                    boolean autoFlush)
                             throws java.io.IOException,
                                    java.lang.IllegalStateException,
                                    java.lang.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.

    Parameters:
    servlet - The Servlet that is associated with this PageContext
    request - The currently pending request for this Servlet
    response - The currently pending response for this Servlet
    errorPageURL - The value of the errorpage attribute from the page directive or null
    needsSession - The value of the session attribute from the page directive
    bufferSize - The value of the buffer attribute from the page directive
    autoFlush - The value of the autoflush attribute from the page directive
    Throws:
    java.io.IOException - during creation of JspWriter
    java.lang.IllegalStateException - if out not correctly initialized

    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


    setAttribute

    public abstract void setAttribute(java.lang.String name,
                                      java.lang.Object attribute)
    register the name and object specified with page scope semantics
    Throws:
    NullPointerException - if the name or object is null

    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 set
    o - the object to associate with the name
    scope - the scope with which to associate the name/object
    Throws:
    NullPointerException - if the name or object is null
    java.lang.IllegalArgumentException - if the scope is invalid

    getAttribute

    public abstract java.lang.Object getAttribute(java.lang.String name)

    return the object associated with the name in the page scope or null

    Parameters:
    name - the name of the attribute to get
    Throws:
    NullPointerException - if the name is null
    java.lang.IllegalArgumentException - if the scope is invalid

    getAttribute

    public abstract java.lang.Object getAttribute(java.lang.String name,
                                                  int scope)

    return the object associated with the name in the specifed scope or null

    Parameters:
    name - the name of the attribute to set
    scope - the scope with which to associate the name/object
    Throws:
    NullPointerException - if the name is null
    java.lang.IllegalArgumentException - if the scope is invalid

    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

    removeAttribute

    public abstract void removeAttribute(java.lang.String name)
    remove the object reference associated with the specified name

    removeAttribute

    public abstract void removeAttribute(java.lang.String name,
                                         int scope)
    remove the object reference associated with the specified name

    getAttributesScope

    public abstract int getAttributesScope(java.lang.String name)
    Returns:
    the scope of the object associated with the name specified or 0

    getAttributeNamesInScope

    public abstract java.util.Enumeration getAttributeNamesInScope(int scope)
    Returns:
    an enumeration of names (java.lang.String) of all the attributes the specified scope

    getOut

    public abstract JspWriter getOut()
    Returns:
    the current JspWriter stream being used for client response

    getSession

    public abstract javax.servlet.http.HttpSession getSession()
    Returns:
    the HttpSession for this PageContext or null

    getPage

    public abstract java.lang.Object getPage()
    Returns:
    the Page implementation class instance (Servlet) associated with this PageContext

    getRequest

    public abstract javax.servlet.ServletRequest getRequest()
    Returns:
    The ServletRequest for this PageContext

    getResponse

    public abstract javax.servlet.ServletResponse getResponse()
    Returns:
    the ServletResponse for this PageContext

    getException

    public abstract java.lang.Exception getException()
    Returns:
    any exception passed to this as an errorpage

    getServletConfig

    public abstract javax.servlet.ServletConfig getServletConfig()
    Returns:
    the ServletConfig for this PageContext

    getServletContext

    public abstract javax.servlet.ServletContext getServletContext()
    Returns:
    the ServletContext for this PageContext

    forward

    public abstract void forward(java.lang.String relativeUrlPath)
                          throws javax.servlet.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.

    Parameters:
    relativeUrlPath - specifies the relative URL path to the target resource as described above
    Throws:
    javax.servlet.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 caller

    include

    public abstract void include(java.lang.String relativeUrlPath)
                          throws javax.servlet.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:
    javax.servlet.ServletException -  
    java.io.IOException -  
    java.lang.IllegalArgumentException - if the target resource URL is unresolvable
    java.lang.SecurityException - if target resource cannot be accessed by caller

    handlePageException

    public abstract void handlePageException(java.lang.Exception e)
                                      throws javax.servlet.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.

    Parameters:
    e - the exception to be handled
    Throws:
    javax.servlet.ServletException -  
    java.io.IOException -  
    NullPointerException - if the exception is null
    java.lang.SecurityException - if target resource cannot be accessed by caller