servletvaluestack.java

webwork source

/*
* WebWork, Web Application Framework
*
* Distributable under Apache license.
* See terms of license at opensource.org
*/
package webwork.util;

import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.PageContext;

/**
 *	Value stack implementation for a servlet based scenario.
 *
 *	@author Rickard 謆erg ([e-mail])
 * @author Maurice C. Parker ([e-mail])
 *	@version $Revision: 1 $
 */
public class ServletValueStack extends ValueStack
{
   // Constructor ---------------------------------------------------
   public ServletValueStack()
   {
      super();
   }

   /**
    * Get the value stack for a given request. If there is no
    * stack available, create one.
    *
    * @param   request  the request for which a stack shall be returned
    * @return     the value stack
    */
   public static ServletValueStack getStack(ServletRequest request)
   {
      ServletValueStack stack = (ServletValueStack) request.getAttribute(STACK_NAME);
      if (stack == null) {
         stack = new ServletValueStack();
         request.setAttribute(STACK_NAME, stack);
      }
      stack.setRequest(request);
      return stack;
   }

   /**
    * Get the value stack for a given page context. If there is no
    * stack available, create one.
    *
    * @param   context  the page context to associate with the stack
    * @return     the value stack
    */
   public static ServletValueStack getStack(PageContext context)
   {
      ServletRequest request = context.getRequest();
      ServletValueStack stack = (ServletValueStack) request.getAttribute(STACK_NAME);
      if (stack == null) {
         stack = new ServletValueStack();
         request.setAttribute(STACK_NAME, stack);
      }
      stack.setRequest(request);
      stack.setContext(context);
      return stack;
   }

   private ServletRequest request;
   private PageContext context;

   // Private -------------------------------------------------------
   /**
    * Set the request that should be associated with this stack.
    * This is called for each use of the stack so that attributes can be accessed
    * properly.
    */
   private void setRequest(ServletRequest request)
   {
      this.request = request;
   }

   /**
    * Set the page context that should be associated with this stack.
    * This is called for each use of the stack in a JSP context.
    */
   public void setContext(PageContext context)
   {
      this.context = context;
   }

   protected Object findInContext(String id)
   {
      if (context != null) {
         try {
            return context.findAttribute(id); // Used in a JSP environment
         } catch (Exception e) {
            // This exception occurred alot before when the page context was not
            // updated correctly in the stack. I do not know if the comment and
            // code below is correct and needed anymore, but we keep it for safety

            //needed for apparent bug in Resin 2.1.1 :(
            return findAttribute(id);
         }
      } else {
         // If the findInContext method is called outside of a jsp page then there
         // is no page context and this code will execute.
         return findAttribute(id);
      }
   }

   /**
    * Mimic the behaviour of the findAttribute method in the PageContext
    * This method is used when there is no pageContext set for this stack
    * and the findInContext method is called.
    * Look for the attribute in the request, session and application scope
    *
    * @return found value or null
    */
   protected Object findAttribute(String id)
   {
      Object result;

      // First look in the request
      if ((result = request.getAttribute(id)) != null)
         return result;
      // If nothing found then look in the session if there is one
      if (!(request instanceof HttpServletRequest))
         return null;
      HttpSession session = ((HttpServletRequest) request).getSession(false);
      if (session != null)
      {
         if ((result = session.getAttribute(id)) != null)
            return result;
         // Finally look in the application scope
         return session.getServletContext().getAttribute(id);
      }
      // We should really look in the application scope here as well,
      // but we do not have any way of finding it now
      return null;
   }

   /**
    * Get parameter directly from request
    */
   protected Object getParameter(String aName)
   {
      return request.getParameter(aName);
   }

}