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Jetty example source code file (PageContext.java)

This example Jetty source code file (PageContext.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Jetty tags/keywords

errordata, exception, http, io, ioexception, ioexception, jsp, pagecontext, pagecontext, request, request, response, servlet, servletexception, servletexception, servletrequest, servletresponse, string, string, xxx

The Jetty PageContext.java source code

/**
 *
 * Copyright 2003-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//

package javax.servlet.jsp;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.tagext.BodyContent;

/**
 * <p>
 * PageContext extends JspContext to provide useful context information for
 * when JSP technology is used in a Servlet environment.
 * <p>
 * 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
 * to the pageContext automatically.
 *
 * <p> 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().
 *
 * <p> An example of how PageContext, JspFactory, and other classes can be
 * used  within a JSP Page Implementation object is given elsewhere.
 *
 * <p>
 * The PageContext provides a number of facilities to the page/component 
 * author and page implementor, including:
 * <ul>
 * <li>a single API to manage the various scoped namespaces
 * <li>a number of convenience API's to access various public objects
 * <li>a mechanism to obtain the JspWriter for output
 * <li>a mechanism to manage session usage by the page
 * <li>a mechanism to expose page directive attributes to the scripting 
 *     environment
 * <li>mechanisms to forward or include the current request to other active 
 *     _components in the application
 * <li>a mechanism to handle errorpage exception processing
 * </ul>
 *
 * <p>Methods Intended for Container Generated Code
 * <p>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.
 * <p>The methods supporting lifecycle are initialize()
 * and <code>release()
 *
 * <p>
 * The following methods enable the <B>management of nested JspWriter 
 * streams to implement Tag Extensions: <code>pushBody()
 *
 * <p>Methods Intended for JSP authors
 * <p>
 * The following methods provide <B>convenient access to implicit objects:
 * <code>getException(),  getPage()
 * <code>getRequest(),  getResponse(),
 * <code>getSession(),  getServletConfig()
 * and <code>getServletContext().
 *
 * <p>
 * The following methods provide support for <B>forwarding, inclusion
 * and error handling</B>:
 * <code>forward(),  include(),
 * and  <code>handlePageException().
 */

abstract public class PageContext 
    extends JspContext
{
    
    /**
     * Sole constructor. (For invocation by subclass constructors, 
     * typically implicit.)
     */
    public PageContext() {
    }
    
    /**
     * Page scope: (this is the default) the named reference remains available
     * in this PageContext until the return from the current Servlet.service()
     * invocation.
     */

    public static final int PAGE_SCOPE		= 1;

    /**
     * Request scope: the named reference remains available from the 
     * ServletRequest associated with the Servlet until the current request 
     * is completed.
     */

    public static final int REQUEST_SCOPE	= 2;

    /**
     * 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.
     */

    public static final int SESSION_SCOPE	= 3;

    /**
     * Application scope: named reference remains available in the 
     * ServletContext until it is reclaimed.
     */

    public static final int APPLICATION_SCOPE	= 4;

    /**
     * Name used to store the Servlet in this PageContext's nametables.
     */

    public static final String PAGE = "javax.servlet.jsp.jspPage";

    /**
     * Name used to store this PageContext in it's own name table.
     */

    public static final String PAGECONTEXT = "javax.servlet.jsp.jspPageContext";

    /**
     * Name used to store ServletRequest in PageContext name table.
     */

    public static final String REQUEST = "javax.servlet.jsp.jspRequest";

    /**
     * Name used to store ServletResponse in PageContext name table.
     */

    public static final String RESPONSE = "javax.servlet.jsp.jspResponse";

    /**
     * Name used to store ServletConfig in PageContext name table.
     */

    public static final String CONFIG = "javax.servlet.jsp.jspConfig";

    /**
     * Name used to store HttpSession in PageContext name table.
     */

    public static final String SESSION = "javax.servlet.jsp.jspSession";
    /**
     * Name used to store current JspWriter in PageContext name table.
     */

    public static final String OUT = "javax.servlet.jsp.jspOut";

    /**
     * Name used to store ServletContext in PageContext name table.
     */

    public static final String APPLICATION = "javax.servlet.jsp.jspApplication";

    /**
     * Name used to store uncaught exception in ServletRequest attribute 
     * list and PageContext name table.
     */

    public static final String EXCEPTION = "javax.servlet.jsp.jspException";

    /**
     * <p>
     * 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.
     *
     * <p>
     * This method is typically called from JspFactory.getPageContext() in
     * order to initialize state.
     *
     * <p>
     * This method is required to create an initial JspWriter, and associate
     * the "out" name in page scope with this newly created object.
     *
     * <p>
     * This method should not be used by page  or tag library authors.
     *
     * @param servlet The Servlet that is associated with this PageContext
     * @param request The currently pending request for this Servlet
     * @param response The currently pending response for this Servlet
     * @param errorPageURL The value of the errorpage attribute from the page 
     *     directive or null
     * @param needsSession The value of the session attribute from the 
     *     page directive
     * @param bufferSize The value of the buffer attribute from the page 
     *     directive
     * @param autoFlush The value of the autoflush attribute from the page 
     *     directive
     *
     * @throws IOException during creation of JspWriter
     * @throws IllegalStateException if out not correctly initialized
     * @throws IllegalArgumentException If one of the given parameters
     *     is invalid
     */
 
    abstract public void initialize(Servlet servlet, ServletRequest request, 
        ServletResponse response, String errorPageURL, boolean needsSession, 
        int bufferSize, boolean autoFlush)  
        throws IOException, IllegalStateException, IllegalArgumentException;

    /**
     * <p>
     * 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().
     *
     * <p>
     * Subclasses shall envelope this method.
     *
     * <p>
     * This method should not be used by page  or tag library authors.
     *
     */

    abstract public void release();

    /**
     * The current value of the session object (an HttpSession).
     *
     * @return the HttpSession for this PageContext or null
     */

    abstract public HttpSession getSession();

    /**
     * The current value of the page object (In a Servlet environment, 
     * this is an instance of javax.servlet.Servlet).
     *
     * @return the Page implementation class instance associated 
     *     with this PageContext
     */

    abstract public Object getPage();


    /**
     * The current value of the request object (a ServletRequest).
     *
     * @return The ServletRequest for this PageContext
     */

    abstract public ServletRequest getRequest();

    /**
     * The current value of the response object (a ServletResponse).
     *
     * @return the ServletResponse for this PageContext
     */

    abstract public ServletResponse getResponse();

    /**
     * The current value of the exception object (an Exception).
     *
     * @return any exception passed to this as an errorpage
     */

    abstract public Exception getException();

    /**
     * The ServletConfig instance.
     *
     * @return the ServletConfig for this PageContext
     */

    abstract public ServletConfig getServletConfig();

    /**
     * The ServletContext instance.
     * 
     * @return the ServletContext for this PageContext
     */

    abstract public ServletContext getServletContext();

    /**
     * <p>
     * This method is used to re-direct, or "forward" the current 
     * ServletRequest and ServletResponse to another active component in 
     * the application.
     * </p>
     * <p>
     * If the <I> relativeUrlPath  begins with a "/" then the URL specified
     * is calculated relative to the DOCROOT of the <code> 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.
     * </p>
     * <p>
     * It is only valid to call this method from a <code> Thread 
     * executing within a <code> _jspService(...)  method of a JSP.
     * </p>
     * <p>
     * Once this method has been called successfully, it is illegal for the
     * calling <code> Thread  to attempt to modify the 
     * ServletResponse </code> object.  Any such attempt to do so, shall result
     * in undefined behavior. Typically, callers immediately return from 
     * <code> _jspService(...)  after calling this method.
     * </p>
     *
     * @param relativeUrlPath specifies the relative URL path to the target 
     *     resource as described above
     *
     * @throws IllegalStateException if <code> ServletResponse  is not 
     *     in a state where a forward can be performed
     * @throws ServletException if the page that was forwarded to throws
     *     a ServletException
     * @throws IOException if an I/O error occurred while forwarding
     */

    abstract public void forward(String relativeUrlPath) 
        throws ServletException, IOException;

    /**
     * <p>
     * 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.
     * </p>
     * <p>
     * The current JspWriter "out" for this JSP is flushed as a side-effect
     * of this call, prior to processing the include.
     * </p>
     * <p>
     * If the <I> relativeUrlPath  begins with a "/" then the URL specified
     * is calculated relative to the DOCROOT of the <code>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.
     * </p>
     * <p>
     * It is only valid to call this method from a <code> Thread 
     * executing within a <code> _jspService(...)  method of a JSP.
     * </p>
     *
     * @param relativeUrlPath specifies the relative URL path to the target 
     *     resource to be included
     *
     * @throws ServletException if the page that was forwarded to throws
     *     a ServletException
     * @throws IOException if an I/O error occurred while forwarding
     */
    abstract public void include(String relativeUrlPath) 
        throws ServletException, IOException;

    /**
     * <p>
     * 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 current JspWriter returned by a call to getOut().
     * </p>
     * <p>
     * If flush is true, The current JspWriter "out" for this JSP 
     * is flushed as a side-effect of this call, prior to processing 
     * the include.  Otherwise, the JspWriter "out" is not flushed.
     * </p>
     * <p>
     * If the <i>relativeUrlPath begins with a "/" then the URL specified
     * is calculated relative to the DOCROOT of the <code>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.
     * </p>
     * <p>
     * It is only valid to call this method from a <code> Thread 
     * executing within a <code> _jspService(...)  method of a JSP.
     * </p>
     *
     * @param relativeUrlPath specifies the relative URL path to the 
     *     target resource to be included
     * @param flush True if the JspWriter is to be flushed before the include,
     *     or false if not.
     *
     * @throws ServletException if the page that was forwarded to throws
     *     a ServletException
     * @throws IOException if an I/O error occurred while forwarding
     * @since 2.0
     */
    abstract public void include(String relativeUrlPath, boolean flush) 
	throws ServletException, IOException;

    /**
     * <p>
     * This method is intended to process an unhandled 'page' level
     * exception by forwarding the exception to the specified
     * error page for this JSP.  If forwarding is not possible (for
     * example because the response has already been committed), an
     * implementation dependent mechanism should be used to invoke
     * the error page (e.g. "including" the error page instead).
     *
     * <p>
     * If no error page is defined in the page, the exception should
     * be rethrown so that the standard servlet error handling
     * takes over.
     *
     * <p>
     * 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.
     *
     * <p>
     * This method is kept for backwards compatiblity reasons.  Newly
     * generated code should use PageContext.handlePageException(Throwable).
     *
     * @param e the exception to be handled
     *
     * @throws ServletException if an error occurs while invoking the error page
     * @throws IOException if an I/O error occurred while invoking the error
     *     page
     * @throws NullPointerException if the exception is null
     *
     * @see #handlePageException(Throwable)
     */

    abstract public void handlePageException(Exception e) 
        throws ServletException, IOException;

    /**
     * <p>
     * This method is intended to process an unhandled 'page' level
     * exception by forwarding the exception to the specified
     * error page for this JSP.  If forwarding is not possible (for
     * example because the response has already been committed), an
     * implementation dependent mechanism should be used to invoke
     * the error page (e.g. "including" the error page instead).
     *
     * <p>
     * If no error page is defined in the page, the exception should
     * be rethrown so that the standard servlet error handling
     * takes over.
     *
     * <p>
     * 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.
     *
     * <p>
     * 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.
     *
     * @param t the throwable to be handled
     *
     * @throws ServletException if an error occurs while invoking the error page
     * @throws IOException if an I/O error occurred while invoking the error
     *     page
     * @throws NullPointerException if the exception is null
     *
     * @see #handlePageException(Exception)
     */

    abstract public void handlePageException(Throwable t) 
        throws ServletException, IOException;

    /**
     * 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.
     *
     * @return the new BodyContent
     */

    public BodyContent pushBody() {
        return null; // XXX to implement
    }
         

    /**
     * Provides convenient access to error information.
     *
     * @return an ErrorData instance containing information about the 
     * error, as obtained from the request attributes, as per the 
     * Servlet specification.  If this is not an error page (that is,
     * if the isErrorPage attribute of the page directive is not set
     * to "true"), the information is meaningless.
     *
     * @since 2.0
     */
    public ErrorData getErrorData() {
	return new ErrorData( 
	    (Throwable)getRequest().getAttribute( "javax.servlet.error.exception" ),
	    ((Integer)getRequest().getAttribute( 
		"javax.servlet.error.status_code" )).intValue(),
	    (String)getRequest().getAttribute( "javax.servlet.error.request_uri" ),
	    (String)getRequest().getAttribute( "javax.servlet.error.servlet_name" ) );
    }
    
}

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