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setting / accessgin Java Bean between page and servlet.

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posted 14 years ago

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I am new to JSP. I wanted to send bean object from page to servlet and then change bean's data in servlet and then set it back to the page. So I created a bean and included it in the page as below

<jsp:useBean id="beanobj" class="mypkg.mybean" scope="application" />

When it try to get data in servlet using the following code, I get error. Null pointer exception.

mybean beanobj = new mybean();
beanobj = (mybean)req.getAttribute("beanobj");

I have tried both with and without following tag
<jsp:setProperty name="beanobj" property="*"/>

This is one part of the problem. javascript:emoticon('

');

The other part is that I want to set the bean data in servlet and then send that bean to page so that by making --> this code <%=beanobj.getName%> as the value of my html text box, I could see the value from bean. This does not work, however if I use EL, that works i.e. ${beanobj.name}.

Can any one help me as to how could I use <jsp:useBean tag and yet achieve the functionality to send bean back and forth between servlet and page. I have explored JSTL but not interested in it yet because first I wanna get a good grip on simple JSP and Servlets and be able to move data between these two layers.

Many thanks in advance.

Bear Bibeault

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posted 14 years ago

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If you put something away in the hall closet, would you go look for it later in the pantry?

Similarly, if you put a scoped variable into application scope, you will not later find it in request scope where you did not put it.

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Faisal A. Khan

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posted 14 years ago

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Bear Bibeault wrote:If you put something away in the hall closet, would you go look for it later in the pantry?

Similarly, if you put a scoped variable into application scope, you will not later find it in request scope where you did not put it.

I have tried with all possibilities of what "scope" offers. Meaning by, session, page, application and request. Nothing works.
Any bright idea . . . ?

Alok Kushwah

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posted 14 years ago

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Scope of bean is application context scope, so try to get it from application not from request. To get it from application use ServletContext.

Bear Bibeault

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posted 14 years ago

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Faisal A. Khan wrote:Any bright idea . . . ?

Yes, look for an item in the same closet that you put it in.

If you put it in application scope, that's where you need to fetch it from.

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Faisal A. Khan

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WHAT AM I MISSING.... I have got the same reply from many sources and nothing seem to work for me. Following is my source code.

JSP Code:

Servlet Code:

package mypkg;
import java.util.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import mypkg.mybean;
public class MyServlet extends HttpServlet {
  public void init(ServletConfig conf) throws ServletException  {
    super.init(conf);
  }
  public void doPost (HttpServletRequest req, HttpServletResponse res)
      throws ServletException, IOException {

HttpSession session = req.getSession(false);

if (session == null) {
	      res.sendRedirect("http://localhost:8080/error.html");
	    }
	    String errPoint;
	    errPoint="00";

try{
		errPoint = "01";
		mybean beanobj = new mybean();

errPoint = "02";		
		beanobj = (mybean)req.getAttribute("beanobj");
		String v_age;	    
		String v_name;

errPoint = "03";
		v_name = beanobj.getAge();

errPoint = "04";
		beanobj.setAge(beanobj.getName());

errPoint = "05";
		beanobj.setName(v_name);

errPoint = "06";
		req.setAttribute("beanobj",beanobj);

errPoint = "07";

String url="/InputForm.jsp";
		ServletContext sc = getServletContext();
		RequestDispatcher rd = sc.getRequestDispatcher(url);
		rd.forward(req,res);
	      
	    }
	    catch (Exception ex){
	    	System.out.println(errPoint);
	    	System.out.println(ex);
	    }
      }
}

My Bean Code:

Bauke Scholtz

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posted 14 years ago

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You're missing the fact that you shouldn't be using scriptlets for this. You should in no way use scriptlets in JSP.

Use EL. Use for example ${beanobj.name} instead of <%= beanobj.getName() %>.

Bear Bibeault

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posted 14 years ago

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Please be sure to use code tags when posting code to the forums. Unformatted code is extremely hard to read and many people that might be able to help you will just move along to posts that are easier to read. Please read this for more information.

You can go back and change your post to add code tags by clicking the

button on your post.

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Bear Bibeault

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posted 14 years ago

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You are placing the bean in request scope during the execution of the JSP. When the JSP finishes executing, the response is sent to the browser and the request is dismissed. So are any scoped variables in request context. So when the page is submitted, the bean has long since been gone and cannot be retrieved from the servlet. This is basic HTTP.

The fact that you are trying to send a bean from a JSP to a servlet indicates a few problems. First, that you do not yet understand how JSP and HTTP requests work, and second, probably indicates a design flaw of some sort.

For the former issue, please read this article. Then you may in a position to determine where your design flaw lies.

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Bear Bibeault

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posted 14 years ago

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Bauke Scholtz wrote:You're missing the fact that you shouldn't be using scriptlets for this.

While I agree that scriptlets should not be used in JSP pages, that's the least of the poster's problem at this point.

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Faisal A. Khan

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posted 14 years ago

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Bear Bibeault wrote:You are placing the bean in request scope during the execution of the JSP. When the JSP finishes executing, the response is sent to the browser and the request is dismissed. So are any scoped variables in request context. So when the page is submitted, the bean has long since been gone and cannot be retrieved from the servlet. This is basic HTTP.

The fact that you are trying to send a bean from a JSP to a servlet indicates a few problems. First, that you do not yet understand how JSP and HTTP requests work, and second, probably indicates a design flaw of some sort.

For the former issue, please read this article. Then you may in a position to determine where your design flaw lies.

From your responce:

So when the page is submitted, the bean has long since been gone and cannot be retrieved from the servlet. This is basic HTTP.

If this is the case, then what good are "req" and "res" in the doPost method ?

Will "req" be long gone when it is used in the doPost method ? I doubt it . . . ! I am totally new to JSP but it really hunts me if we can not use these "req" and "res" objects.
Please see this page
MVC in JSP
section Listing 3: ShoppingServlet.java . I learned getting parameters and other stuff from this site and tried to get the bean object the same way and ran in to this problem of Null pointer exception. If there is some design problem, then compared to the URL of MVC, what exactly is wrong in my desgin . . . ?

Sorry for not posting the code properly earlier. I appreciate your help in this regard.

Thanks and look forward

Balu Sadhasivam

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posted 14 years ago

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Faisal A. Khan wrote:
Will "req" be long gone when it is used in the doPost method ? I doubt it . . . ! I am totally new to JSP but it really hunts me if we can not use these "req" and "res" objects.

you misunderstood Bear's quote..

This is nothing to do with JSP .. its basic that request originates from client say, HTML ( after all are intrepreted as HTML ) and posted to server either using GET or POST method , which is handled by Servlet/JSP container (depending on whats your action is ) .

The request parameters ('req' which you mean) is used by doPost to process the input values and take appropriate action by calling another utility class , bean or redirests to JSP... The response is generated then and sent back to the client by Container. Thats it the scope of request and response attributes are gone by now.. and no way to gain it... and if you want to use some attributes between requests then "session" comes to picture..