How to pass a value of a variable from a java class to the jsp page

Seems like you're doing AJAX, so I'd say your response would need to be encoded in an AJAX-compatible way (JSON, XML, ...).

If you do AJAX-encoding, your function might look like this:

function(response){ var toplevel = response.<your_top_level_element>;} 

Edit:

We're using JSON Simple for JSON encoding.

Our Java backend then looks like this (simplified version without error checking):

public String execute(){  JSONObject jsonResult = new JSONObject();  jsonResult.put( "result", "ok");  return jsonResult.toJSONString();}

And in the Javascript function:

function(response){ var result = response.result; //now yields "ok"}

From your code,

request.setAttribute("rest", res);

You shouldn't set it as request attribute. Setting request attributes is only useful if you're forwarding to a JSP file. You need to write it straight to the response yourself. Replace the line by

response.getWriter().write(res);

This way it'll end up in the response body and be available as variable response in your JS function.

See also:

• How to update current page by Servlet/Ajax?

If this is an ajax request, you can forward the request into another jsp page rather than return. With this

getServletContext().getRequestDispatcher("/ajax.jsp").forward(request, response);create the jsp page(ajax.jsp) on your webcontent and add this sample code.<p>${rest}</p> <!-- Note: You can actually design your html here.      You can also format this as an xml file and let your js do the work.//-->

Another way is replace your System.out.println with this

PrintWriter out = response.getWriter();out.print("The value of res been passed is "+res);

but I guess this is a bad practice. See example here.