Reading JSon String with Gson

Question

I've been pursing around Google trying to figure this out, but I can't seem to do it. I have the following json string that is returned to my java applet from another source that i need to interact with.

{
 "A01": {"Status": "Ready", "Time": "00:00"}, 
 "A02": {"Status": "Ready", "Time": "00:00"}, 
 ......
}

At the moment I'm not sure how i should use Gson to parse that into my applet. When i talked to the designers of that program. The json string was designed for use in php not java so when i decoded it in php it gave me a good multi-dimensional assoc array.

Any suggestions on this.

Answer 1

An associative array in PHP translates to a Map in Java. So, in Gson's eyes, your JSON is in format of Map<String, Event> where the Event class has the fields status and time.

public class Event {
    private String Status;
    private String Time;

    // Add/generate getters, setters and other boilerplate.
}

Yes, capitalized field names are ugly, but that's how your JSON look like. You would otherwise need to create a custom Gson deserializer.

Here's how you can convert it.

Map<String, Event> events = new Gson().fromJson(json, new TypeToken<Map<String, Event>>(){}.getType());

A01, A02, etc become Map keys and its value becomes the Event value of Map. You may want to add another custom deserializer to get the Time into a java.util.Date.

As a different alternative, you can also use Map<String, Map<String, String>> instead.

Answer 2

That link pointed me to something i wasn't even looking at. I also forgot to mention in my post that Knowing the A01, A02, etc is very important. But a link in the post that you pointed me to lead me to come up with this which works for me.

JsonParser parse = new JsonParser();
JsonObject jobj = (JsonObject)parse.parse(status);                            
Set<Map.Entry<String, JsonElement>> map = jobj.entrySet();
Iterator<Map.Entry<String, JsonElement>> iterator = map.iterator();
int size = map.size();
for( int k = 0; k < size; k++ )
{
    Map.Entry<String, JsonElement> entry = iterator.next();
    String key = entry .getKey();
    JsonObject jele = (JsonObject)entry.getValue();
}

Answer 3

If your json was slightly different, like below:

{
 [
  {"Status": "Ready", "Time": "00:00"}, 
  {"Status": "Ready", "Time": "00:00"}, 
  ......
 ]
}

Gson would be able to convert the json into a collection of objects, the object you would have to define yourself. So you would need:

public class myAClass {
public String Status;
public Double time; //this could be a string/or even a Date I guess, 
                    //not sure what data you are expecting
                    //and the colon may cause a problem if parsed as a double
}

And then use that like so:

Type listType = new TypeToken<List<myAClass>>() {}.getType();
List<myAClass> myAClassList = new Gson().fromJson(json, listType); 
//where json is yr json string

You could then use the list of objects as you require.

(further reading over here)