Convert Number to int? incompatible types found : void required: int

Question

I am writing an application to get latitude, longitude of a position in a google map using java and javascript.

The below code part gives an error:

code(It's a part of a jsp file):

<script type="text/javascript">
  var map;

  //Initialization & some more code goes here

  function centerChanged() {
    <%
        int lat=0,lng=0;
        lat=%>map.getCenter().lat();<%
        lng=%>map.getCenter().lng();<%
        //request.setAttribute("lat", lat);
        //request.setAttribute("lng", lng);
    %>    
  }

From the above code, these are the two lines that cause the error:

    lat=%>map.getCenter().lat();<%
    lng=%>map.getCenter().lng();<%

Additional Information:

map.getCenter().lat() << This will return a Number as mentioned in google maps API:

This is the error I am getting:

org.apache.jasper.JasperException: PWC6033: Error in Javac compilation for JSP

PWC6197: An error occurred at line: 81 in the jsp file: /maptest.jsp PWC6199: Generated servlet error: string:///maptest_jsp.java:127: incompatible types found : void required: int

PWC6197: An error occurred at line: 82 in the jsp file: /maptest.jsp PWC6199: Generated servlet error: string:///maptest_jsp.java:130: incompatible types found : void required: int

Can anyone please tell what is wrong?

Could you give us a more detailed picture of what your JSP code looks like? Are lat and lng Java variables or JavaScript variables? — Joachim Sauer
I'm new to posting; So please mention if I need to add more information/code. — Dilini
If lat and lng are supposed to be Java/JSP variables and map.getCenter().lat(); is JavaScript code then, the posted code can not work: JavaScript is executed one the client and after the JSP code is executed on the server. So you can't assign a JS value to a Java/JSP variable this way. — Joachim Sauer
@JoachimSauer: I see. Thanks! So, to get map.getCenter().lat() value to a java variable(int lat), should I declare map as a java variable(not a javascript variable)? Can that be a solution? — Dilini
no, because the Google Maps API always runs on the client. If you need that information back at the server, then you'll need to get it back somehow (using a AJAX request or something similar). — Joachim Sauer

Ilya Saunkin Ilya Saunkin · Accepted Answer · 2011-11-07T11:56:20

You are trying to dynamically insert a value from Javascript into JSP. The mistake is that JSP is executed on the server side, whilst Javascript on client side.

What you wrote there is equal to Java code:

out.write("function centerChanged() {");
int lat=0,lng=0;
lat=;
out.write("map.getCenter().lat();");
lng=;
out.write("map.getCenter().lng();");
//request.setAttribute("lat", lat);
//request.setAttribute("lng", lng);
out.write("}");

Get it? Whatever is surrounded by <%%> is pure Java code, whatever is outside of it, is printed out, hence your exception.

To work around it, you need to change the logic how you retrieve the client-side Javascript values in your server-side JSP code.

Convert Number to int? incompatible types found : void required: int

code(It's a part of a jsp file):

Additional Information:

This is the error I am getting:

2 Answers