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

Question

I have 2 files named Admin.java and index.jsp.

In Admin.java through a function I retrieve the value of the varible named

Answer 1

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.

Answer 2

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?

Answer 3

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"
}