JSP - How to clear the HttpServletRequest

I wish to do is clear up all the parameters and attributes in the request(HttpServletRequest) pass by client, and set a new attribute, and dispatch it to another page, to summarize it in code:

//clear up all the parameters and attributes in the request pass by client<--How to do this
request.setAttribute("NewAttribute", "value");
dispatcher.forward(request, response);

I can't find a method like request.clear(). Is there a corresponding method that can do this?
LVL 9
william007Asked:
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boonlengCommented:
To remove the value in attribute, call request.getAttributeNames() to get all all the attribute names, loop through the names and call request.removeAttribute() to remove it 1 by 1.

parameters value in the request cannot be removed.
0
Mayank SAssociate Director - Product EngineeringCommented:
If you want to forward to a page without having the request, just use response.sendRedirect () instead of RequestDispatcher.forward ()
0
Mayank SAssociate Director - Product EngineeringCommented:
Otherwise you can set the attributes to null but I doubt if you cannot change the values of parameters.
0
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rrzCommented:
This works for me in Tomcat 6.  Please try in your server.
<%@ page import="java.util.*"%>
<%!
  public class Wrapper extends HttpServletRequestWrapper{
     public Wrapper(HttpServletRequest request){
                     super(request);    
     }
     public String getParameter(java.lang.String name){return null;}
     public Map getParameterMap(){return null;}
     public Enumeration getParameterNames(){return null;}
     public String[] getParameterValues(java.lang.String name){return null;}
  }
%>
<%
  Enumeration e = request.getAttributeNames();
  while(e.hasMoreElements()){
     String attName = (String)e.nextElement();
     if(!"javax.servlet.forward.request_uri".equals(attName)
          && !"javax.servlet.forward.context_path".equals(attName)
          && !"javax.servlet.forward.servlet_path".equals(attName)
          && !"javax.servlet.forward.query_string".equals(attName))request.removeAttribute(attName);
  }
   Wrapper wrap = new Wrapper(request);
   wrap.setAttribute("NewAttribute", "someValue");
   RequestDispatcher dispatcher = application.getRequestDispatcher("/destination.jsp");
   dispatcher.forward(wrap, response);
%>
0
rrzCommented:
On second thought, please try this one instead.
<%@ page import="java.util.*"%>
<%!
  public class Wrapper extends HttpServletRequestWrapper{
     public Wrapper(HttpServletRequest request){
                     super(request);    
     }
     public String getParameter(java.lang.String name){return null;}
     public Map getParameterMap(){return null;}
     public Enumeration getParameterNames(){return null;}
     public String[] getParameterValues(java.lang.String name){return null;}
  }
%>
<%
  Enumeration e = request.getAttributeNames();
  while(e.hasMoreElements()){
     String attName = (String)e.nextElement();
     request.removeAttribute(attName);
  }
   Wrapper wrap = new Wrapper(request);
   wrap.setAttribute("NewAttribute", "someValue");
   RequestDispatcher dispatcher = application.getRequestDispatcher("/destination.jsp");
   dispatcher.forward(wrap, response);
%>
hello from requestWrap.jsp<br/>
name is ${param.name}<br/>
location is ${location}<br/>
NewAttribute is ${NewAttribute}<br/>
<%
  Enumeration e2 = request.getAttributeNames();
  while(e2.hasMoreElements()){
     String att = (String)e2.nextElement();
     out.print(att + "=" + request.getAttribute(att) + "<br/>");
  }
%>
0
rrzCommented:
I am sorry. Not the that last one. Try this one.
<%@ page import="java.util.*"%>
<%!
  public class Wrapper extends HttpServletRequestWrapper{
     public Wrapper(HttpServletRequest request){
                     super(request);    
     }
     public String getParameter(java.lang.String name){return null;}
     public Map getParameterMap(){return null;}
     public Enumeration getParameterNames(){return null;}
     public String[] getParameterValues(java.lang.String name){return null;}
  }
%>
<%
  Enumeration e = request.getAttributeNames();
  while(e.hasMoreElements()){
     String attName = (String)e.nextElement();
     request.removeAttribute(attName);
  }
   Wrapper wrap = new Wrapper(request);
   wrap.setAttribute("NewAttribute", "someValue");
   RequestDispatcher dispatcher = application.getRequestDispatcher("/destination.jsp");
   dispatcher.forward(wrap, response);
%>
0

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rrzCommented:
I guess I could make it easier for anyone to test by posting the other pages I used.
The starter HTML is  
---------------------------------------------------
<html><body>
   <a href="http://localhost:8080/forward.jsp?name=rrz">go to http://localhost:8080/forward.jsp</a>
</body></html>
----------------------------------------------------
forward.jsp
-----------------------------------------------------------
<%
  request.setAttribute("location","California");
  RequestDispatcher dispatcher = request.getRequestDispatcher("requestWrap.jsp");
  dispatcher.forward(request, response);
%>
------------------------------------------------------
and then finally,  destination.jsp  
----------------------------------------------------------------
<%@ page import="java.util.*"%>
<html><body>
hello! from destination.jsp<br/>
name is ${param.name}<br/>
NewAttribute is ${NewAttribute}<br/>
location is ${location}<br/>
<%
  Enumeration e2 = request.getAttributeNames();
  while(e2.hasMoreElements()){
     String att = (String)e2.nextElement();
     out.print(att + "=" + request.getAttribute(att) + "<br/>");
  }
%>
</body></html>

0
Mayank SAssociate Director - Product EngineeringCommented:
william, any questions?
0
william007Author Commented:
No question at all, thanks for help:-)
0
Mayank SAssociate Director - Product EngineeringCommented:
:-)
0
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