Dynamic JSON structure to Java structure

I read carefully the comments above and I think there is a very common scenario where an ad hoc Java object would be extremely useful even if the API structure is known at compile time.

Lets say you deal with an API that return a complex JSON object in which you are only interested in a very specific property value.

Take as an example the folowing google map API call to get geo details givin an address:

https://maps.googleapis.com/maps/api/geocode/json?address=sunnyvale,CA

As you can check and see, the response structure is quite complex. Assuming you only want to get the lat and lng properties value, there should be an easier way rather than predefine the complete corresponding Java class.

So yes, if you don't want to go with the strongly typed predefined Java class, you will need to use raw Object type and Maps. More specifically, a StringMap.

And now finally I can give a solution:

Ideally, you would like to access the properties with the same native notation like you would do in JS. Something like this:

String url = "https://maps.googleapis.com/maps/api/geocode/json?address=" + address;
String responseStr = fetch(url);
JsonHelper response =  JsonHelper.forString(responseStr);

String status = (String) response.getValue("status");
if(status != null && status.equals("OK")) {
   lat = (Double) response.getValue("results[0].geometry.location.lat");        
   lng = (Double) response.getValue("results[0].geometry.location.lng");
}

The following JsonHelper class code is taken from the jello-framework and it lets you do exactly that.

package jello.common;

import java.util.List;

import com.google.gson.Gson;
import java.util.AbstractMap;

public class JsonHelper {

    private Object json;

    public JsonHelper(String jsonString) {
        Gson g = new Gson();
        json = g.fromJson(jsonString, Object.class);
    }

    public static JsonHelper forString(String jsonString) {
        return new JsonHelper(jsonString);
    }

    @SuppressWarnings("unchecked")
    public Object getValue(String path) {
        Object value = json;
        String [] elements = path.split("\\.");
        for(String element : elements) {
            String ename = element.split("\\[")[0];

            if(AbstractMap.class.isAssignableFrom(value.getClass())) {
                value = ( (AbstractMap<String, Object>) value).get(ename);

                if(element.contains("[")) {
                    if(List.class.isAssignableFrom(value.getClass())) {
                        Integer index = Integer.valueOf(element.substring(element.indexOf("[")+1, element.indexOf("]")) );
                        value = ((List<Object>) value).get(index);
                    }
                    else {
                        return null;
                    }
                }
            }
            else {
                return null;
            }
        }

        return value;
    }
}