在javascript函数中使用jsp

Question

I've searched for this but can't find anything. Please correct my question if it's incorrect english.

This is my code: EDIT: The code is within my .jsp file!

    function drawChart() {
    var data = google.visualization.arrayToDataTable([
        ['Beoordeling', 'Stage Opleider', 'Student'],

        ['1', '1', '4'],

        <% ArrayList < Stelling > alleStellingenLijst2 = new ArrayList < Stelling > ();
        alleStellingenLijst2 = (ArrayList < Stelling > ) request.getAttribute("stellingen");
        for (Stelling s: alleStellingenLijst2) {
            out.println("['1', '" + s.getDeStelling() + "' , '" + s.getDeWaarde() + "'],");
        } %> ]);
    var options = {
        title: 'Laatste competenties',
        hAxis: {
            title: 'Score',
            titleTextStyle: {
                color: 'green'
            }
        },
        vAxis: {
            title: 'Beoordeling nummer',
            titleTextStyle: {
                color: 'green'
            }
        },
        // Allow multiple simultaneous selections.
        selectionMode: 'multiple',
        colors: ['#BEF781', 'green']
    };
    var chart = new      google.visualization.BarChart(document.getElementById('chart_div'));
    chart.draw(data, options);
}

For some reason, it wont execute the code between the <% %> (from the jsp).

This page online: http://project-omega.appspot.com/grafieken.jsp The google app engine logs say the error is on the last line of my page. It's a nullpointerexception.

I have no idea what it means and I really hope someone can help me.

Thanks a lot and sorry for my english.

EDIT The rendered output looks as follows

  function drawChart() {
    var data = google.visualization.arrayToDataTable([                                               
      ['Beoordeling', 'Stage Opleider', 'Student'],
      for (Stelling s : alleStellingenLijst2) {
        out.println("['1', '" + s.getDeStelling() + "' , '" + s.getDeWaarde() + "'],");       
    }  
  ]);

NEW CODE:

 function drawChart() {
        var data = google.visualization.arrayToDataTable([
          ['Beoordeling', 'Stage Opleider', 'Student'],

          ['1', 1, 4],

          <%

            ArrayList<Stelling> alleStellingenLijst2 =(ArrayList<Stelling>) getServletContext().getAttribute("stellingen");
            for (Stelling s : alleStellingenLijst2) {
                out.println("['1', " + s.getDeStelling() + " , " + s.getDeWaarde() + "],");       
            }   
        %> 
        ['2', 2, 2]
        ]);

Answer 1

These are JSP markups, you cannot use them in JavaScript!

That's because JSP files are compiled to the .java classes during compilation, and JavaScript is executed on the client side.

You could do the opposite - generate a JavaScript code in the JSP file, that way you could pass some data you want to the JS variables.

Answer 2

I suppose you haven't set the stellingen request attribute. You usually set the request attributes in a servlet, before forwarding the request to jsp:

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
    ArrayList<Stelling> list = ...;
    req.setAttribute("stellingen", list);
    req.getRequestDispatcher("/grafieken.jsp").forward(req, resp);
}

Also make sure the attribute is set in the JSP code:

<%
List<Stelling> stellingen = (List<Stelling>) getServletContext().getAttribute("stellingen");
if(stellingen == null) {
    out.println("stellingen attribute not set!");
}else{
    for (Stelling s : stellingen) {
        out.println("['1', " + s.getDeStelling() + " , " + s.getDeWaarde() + "],");       
    }   
}
%>