Complex Json Object to Java object with Map field with Gson

Question

I have a Json structure like so:

{
   "Pojo" : {
       "properties" : {
          "key0" : "value0",
          "key1" : "value1"
       }
   }
}

I want my final result to look something like this:

public class Pojo {
     public Map<String, String> properties;
}

but instead I get something like this:

public class Pojo {
   public Properties properties;
}

public class Properties {
  public String key0;
  public String key1;
}

Right now all I am doing for parsing the Json is this:

new Gson().fromJson(result, Pojo.class)

Thoughts on what I would need to do to get this set up correctly? I do not have the ability to change the Json return object's structure.

iagreen · Accepted Answer · 2015-08-28 02:53:41Z

2

Gson is trying to match the JSON field name to a POJO field, so you above JSON is implying the top level object has a field named 'Pojo'. In fact, it is indicating the following class structure,

class Container {
    MyObject Pojo;
}

class MyObject {
    Map<String, String> properties;
}

where the name of the classes MyObject and Container are completely arbitrary. Gson matches field names, not object type names.

You can deserialize that object with a simple statement -

Container container = gson.fromJson(result, Container.class);

Your map with then be container.Pojo.properties

If you would rather not have the extra container class, you can parse to a Json tree first, and then extra the part that you an interested in --

JsonElement json = new JsonParser().parse(result);
// Note "Pojo" below is the name of the field in the JSON, the name 
// of the class is not important
JsonElement pojoElement = json.getAsJsonObject().get("Pojo");
Pojo pojo = gson.fromJson(pojoElement, Pojo.class);

Then your map is in pojo.properties, which is what I think you want. I have left off error checking for clarity, but you will probably want to add some.

answered Aug 28, 2015 at 2:53

iagreen

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1 Comment

swhite Over a year ago

Thanks for helping me understand what Gson is trying to do here. This is my first attempt with the parser.

Aakash · Accepted Answer · 2015-08-27 23:23:40Z

0

Try this:

JSONObject obj1=new JSONObject(jsonString);
JSONObject obj2=obj1.getJSONObject("Pojo");
JSONObject obj3=obj2.getJSONObject("properties");
String key1=obj3.getString("key0");
String key2=obj3.getString("key1");

For more reference try the link:

https://androidbeasts.wordpress.com/2015/08/04/json-parsing-tutorial/

answered Aug 27, 2015 at 23:23

Aakash

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