Parsing dynamic JSON data with Gson

Question

I'm a beginner Java and Gson user and have been able to apply it to my needs. I now have some JSON data that I need to parse into a spinner as follows:

{
    "lang":[
        "arabic",
        "bengali",
        "dutch-utf8",
        "eng_root",
        "english",
        "english-utf8",
        ...
     ],
     "themes":{
         "blue":{
             "chinese_ibm500":1,
             "spanish":1,
             "bengali":1,
             "japanese":1,
             "english":1,
             "russian":1,
             "french-utf8":1,
             "eng_root":1,
             "arabic":1,
             "spanish-utf8":1,
             "portuguese":1,
             ...
         },
         "green":{
             "eng_root":1,
             "engmonsoon":1,
             "english":1
             ...
         },
         "red":{
             "chinese_ibm500":1,
             "spanish":1,
             "bengali":1,
             ...
         }
    }  
}

So from this JSON I need 2 things:

1) the array under lang is dynamic as for its the languages installed on the server. How could I get all the entries?

I have a class as follows but im stuck as to what I should do after I return lang

public class ListData {

    private List<Language> lang;

    public List<Language> getLang {
        return lang;
    }

    public static class Language {
        ???
    }
}

2) after understanding 1 I might be able to figure this one out. Under themes are colors which again can be more or less {purple, orange, whatever}. I just need a list of those themes, as far as I'm concerned I don't need to know the languages for each.

Feel like this question is turning into a book. I have searched SO extensively and hate asking questions but I'm pretty stumped. Thanks in advance.

You could, of course, just parse it into JSON objects, vs doing the Gson thing. — Hot Licks
– Hot Licks, Commented May 13, 2013 at 21:28

MikO · Accepted Answer · 2013-05-13 21:30:54Z

5

1) In order to get the "lang" array, just modify

private List<Language> lang;

for

private List<String> lang;

Since the elements inside "lang" array are all strings, you don't need any class Language to store those values, they'll be parsed correctly as strings. And it doesn't matter how many strings the array contains...

2) In order to parse "themes", you have to notice that it's not an array [ ], but an object { }, so you do need to parse it with some object, and the most suitable class here is a Map like this:

private Map<String, Object> themes;

Note: as you said that you don't need the data under "blue", "green", etc... you can just Object as the value type in the map, otherwise you'd need some class...

Using a Map here allows you to have an arbitrary number of themes in your JSON response.

So in summary, you just need a class like:

public class ListData {

    private List<String> lang;
    private Map<String, Object> themes;

    //getters & setters
}

and parse your JSON with:

Gson gson = new Gson();
ListData data = gson.fromJson(yourJsonString, ListData.class);

Your list of langs will be under:

data.getLang();

and your list of themes will be under:

data.getThemes().keySet();

I suggest you to take a look at Gson documentation. It's quite short and clear and you'll understand everything much better...

edited May 13, 2013 at 21:30

answered May 13, 2013 at 21:09

MikO

18.8k13 gold badges81 silver badges112 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Eddie Garcia Over a year ago

Thanks alot. I actually tried this before but I was getting errors about expecting array but was object or the sorts but I only had created for lang and not for themes in ListData. Actually checking my JSON response I get themes coming before lang and when I edited my ListData with the map this time it now works. So I'm assuming that GSON didn't know how to parse themes? Incredible...

Eddie Garcia Over a year ago

As a mini question, lets say there was lang, themes, and fonts. If i just wanted lang and themes would the above answer work by itself or would I have to create an object to handle fonts and just never use it?

MikO Over a year ago

It doesn't matter if you have more objects in your JSON apart from lang and themes... Gson just process your class and compare the name of the class attributes with the JSON elements names... If a class attribute match the name of the element found in the JSON, it tries to pase the content of the JSON element into the class attribute... If there's some element in your JSON that doesn't match any class attribute name, Gson just ignore that element...

Collectives™ on Stack Overflow

Parsing dynamic JSON data with Gson

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related