An example of a javascript function passing JSON data to a Java applet

Question

I have just started developing applets. I want to be able to pass (JSON) data from a javascript function, to a method in my applet.

Although I have searched, I cannot find a suitable example that shows how to do this. Can someone please either show a link to a resource that shows how to do that, or paste a few lines in here to show how to do that.

Also, I have the ff questions:

1. is there a limit to the size of JSON string that can be passed from JSON to the applet? (if yes - what is it?)
2. Is it possible to compress (zip) a long string before passing it from JSON to the applet?

Answer 1

On the JavaScript side, you should use JSON2 to convert your data to JSON text, using the code

var jsn = JSON.stringify({"x": "y"});

Then you pass it to the applet:

var applet = document.getElementById("myApplet");
applet.setJSONData(jsn);

You need, of course, to have a public method on your applet that you can call. On the Java side, you can use Jackson to parse the JSON to Java hashmaps or to beans:

public class MyApplet extends JApplet {
    public void setJSONData(String data) {
        ObjectMapper mapper = new ObjectMapper();
        Map map = mapper.readValue(data, Map.class);
        // TODO sth with map
    };
}

Be careful with encodings of non-ASCII characters, it seems that the JSON produced in the browser is not always UTF-8, it may depend on browser vendor or HTML page encoding.

If you are really adventurous you could experiment with JSObject in Java Plugin 2, instead of using JSON.