How to convert from JSON to JSONP?

Question

I coded the following to send JSON data to the front end. But due to cross-domain security woes we need to convert it to JSONP, can someone suggest what I need to modify for this conversion?

Server side Code

JsonFactory jfactory = new JsonFactory();
         ObjectMapper mapper = new ObjectMapper();
         try {
                StringWriter stringWriter = new StringWriter();
                JsonGenerator jGenerator = jfactory.createJsonGenerator(stringWriter);
                jGenerator.useDefaultPrettyPrinter();
                jGenerator.writeStartObject(); // {
                jGenerator.writeStringField("title", title); // "title" : title
                jGenerator.writeStringField("Description", desc); // "desc" :
                jGenerator.writeFieldName("images");
                jGenerator.writeStartArray(); // [
                if(imageArray.size() != 0){
                for (String img : imageArray) {
                    jGenerator.writeString(img); // "msg 1"
                }
                }
                jGenerator.writeEndArray(); // ]
                jGenerator.writeEndObject(); // }
                jGenerator.close();
                response.getWriter().write(stringWriter.toString());
                System.out.println(stringWriter.toString());
                response.getWriter().close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("JasonGen servlet called end");

Front-end Javascript:

$.getJSON("http://localhost:8080/JsoupPrj/JasonGen?url="+ url[0],function(data){
                var imageArray=[];
                var imageOne = null;
                    imageArray=data.images;
....................
}

Answer 1

Since you're using jQuery and you control the server-side, change your server code so that it looks for the callback parameter. The value of this parameter will be the name of the callback function that the client-side code is expecting. Then instead of returning the bare JSON, return it in the form: callbackName(rawJson).

For instance, assuming a servlet API:

String callbackName = request.getParameter("callback");

// ... your JSON code 

if (callbackName != null)
{
    // JSONP wrapping:
    response.getWriter().write(callbackName +
                               "(" + stringWriter.toString() + ")");
    System.out.println(callbackName + "(" + stringWriter.toString() + ")");
}
else
{
    response.getWriter().write(stringWriter.toString());
    System.out.println(stringWriter.toString());
}

response.getWriter().close();

Then on the client-side, continue to use jQuery.getJSON, but append a ?callback=? query parameter to your URL, or instead use jQuery.ajax for your call, and use the dataType: jsonp setting.