How to go about passing the data from Java Servlet to JavaScript

Question

I have this code:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    PrintWriter printWriter = response.getWriter();
    JSONArray arrayObj=new JSONArray();

    TimeTableDAO timeTable = new TimeTableDAO();
    ArrayList<String[]> data = timeTable.getTimeTableData();

    for (int i = 0; i < data.size(); i++){
        for (int j = 0; j < data.get(i).length; j++){
            printWriter.print("Token  " + data.get(i)[j] + "\n");

        }
    }

    response.sendRedirect("script.js");
    response.getWriter().write(data.toString());
}

Within my javascript file, once the page is loaded and everything is rendered it will fire this off:

$(window).on('load', function() {
$.get("TeacherServlet", function(response) {
    console.log(response);
});
});

I am trying to pass the data that I have in my servlet back to javascript so that I can do other things to the data using Jquery. However I want this data to be passed back as a JSON format.

Please can someone help me do that. Thanks in advance :)

ControlAltDel · Accepted Answer · 2017-07-28T20:01:31.677

2

So add everything to your JSONArray and then write that to the response

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    PrintWriter printWriter = response.getWriter();
    JSONArray arrayObj=new JSONArray();

    TimeTableDAO timeTable = new TimeTableDAO();
    ArrayList<String[]> data = timeTable.getTimeTableData();

    for (int i = 0; i < data.size(); i++){
        for (int j = 0; j < data.get(i).length; j++){
            arrayObj.put(data.get(i)[j]); // instead of writing directly, add it to the JSONArray.
        }
    }
    printWriter.println(arrayObj.toString()); //write the JSONArray to the response
    response.sendRedirect("script.js");
    //response.getWriter().write(data.toString()); //this doesn't do what you want


}

edited Jul 28 '17 at 20:01

answered Jul 28 '17 at 19:59

ControlAltDel

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response.println(arrayObj.toString()); ?? what does this do ? println ? – dark_illusion_909099 Jul 28 '17 at 20:01
@dark_illusion_909099 sorry that should have been printWriter I have corrected in my response – ControlAltDel Jul 28 '17 at 20:02
I get 500 (Internal Server Error) however I am not sure what the cause of it – dark_illusion_909099 Jul 28 '17 at 20:05
Sorry I was missing the json jar that's why I was getting the error – dark_illusion_909099 Jul 28 '17 at 20:31

DwB · Answer 2 · 2017-07-28T20:24:40.963

0

You have a number of issues:

Add the data that you want to transfer from the Servlet to the destination page as a request attribute.
Do not redirect to the js file. Instead, in the Servlet, get a RequestDispatcher from the request object and dispatch the request to the target resource (in your case, the js file).
In the js file, you will need to retrieve the parameter values from the request.

Edit

Additional information.

Do some reading about Java Servlet development. Consider a google search for "java servlet development tutorial".
Bookmark the JEE JavaDoc and do some reading. HttpServletRequest is a good place to start.
request.setAttribute(attributeName, attributeValue);
request.getRequestDispatcher(stringPathToTargetResource);
For the JS code, you are on your own. try a google search for "get request attribute with javascript". Here is a StackOverflow post that discusses this topic.

edited Jul 28 '17 at 20:24

answered Jul 28 '17 at 20:10

DwB

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Can you show that as an example ? – dark_illusion_909099 Jul 28 '17 at 20:11
an example of which step? – DwB Jul 28 '17 at 20:11
All of the steps you mentioned above – dark_illusion_909099 Jul 28 '17 at 20:12
@DwB I think you are confused... Maybe I'm confused(?). The request parameter is set by the client, not the servlet, or? Unless you redirect the URL... – ControlAltDel Jul 28 '17 at 20:38
@ControlAltDel You are confused. If you want to pass data from a Servlet to a resource, the Servlet will need to add the data to the Request. – DwB Jul 28 '17 at 20:55
Based on the accepted response, it looks like OP wanted to know how to set the response body. – DwB Jul 28 '17 at 20:57

How to go about passing the data from Java Servlet to JavaScript

2 Answers2