Java Gson serialize json into an object

Question

I have the following Item class:

public class Item {
    public Object item;
}

I am inserting a JSON into this object using GSON.

tmp =

{
    "_id": {
        "$oid": "5076371389d22e8906000000"
    },
    "item": {
        "values": [
            {
                "value1": [
                    4958,
                    3787,
                    344
                ],
                "value2": [
                    4,
                    13,
                    23
                ]
            }
        ], 
        "name": "item1"
    }
}

Java bit:

Item item = new Item();
Gson g = new Gson();
it = g.fromJson(tmp.toString(), Item.class);

it.item becomes a StringMap type (http://code.google.com/p/google-gson/source/browse/trunk/gson/src/main/java/com/google/gson/internal/StringMap.java?r=1131)

I now need to access the sub-objects within this object. I can use the overridden toString function this type has which prints all objects within this object. But how would I be able to navigate through it? P.S. The reason I put everything into an object datatype not a structured class is that the JSON structure varies each time, so I can't really have a class schema. Any suggestions?

Community · Accepted Answer · 2017-05-23 10:28:01Z

2

You should create an object structure that reflects the JSON instead (since this is what you're trying to do anyway). For your example, you could use this:

public class MyObject {
    private Item item;
    private String _id;

    // getters, setters, etc.
}

public class Item {
    private List<Value> values;
    private String name;

    // getters, setters, etc.
}

public class Value {
    private List<Integer> values1;
    private List<Integer> values2;

    // getters, setters, etc.
}

Then pass MyObject.class to Gson:

MyObject myObj = g.fromJson(tmp.toString(), MyObject.class);

You can get the lists in values like so:

List<Integer> values1 = myObj.getItem().getValues().get(0).getValues1();
List<Integer> values2 = myObj.getItem().getValues().get(0).getValues2();

Try that and see if it works.

Also, you should check out my answer to a similar question here, specifically the part at the end about how to write an object structure for Gson based on some JSON object.

edited May 23, 2017 at 10:28

CommunityBot

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answered Oct 11, 2012 at 21:19

Brian

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2 Comments

Brian Over a year ago

Ah, I didn't see the end of your question, sorry. How much does the JSON structure vary?

Reza Over a year ago

It is generated from an unstructured dataset. The only thing that remains the same is Item object.

zurbergram · Accepted Answer · 2013-04-16 18:45:23Z

0

You can always create a constructor for the custom object that uses reflection and takes the StringMap

public MyObject(StringMap sm){
    Iterator it = sm.entrySet().iterator();
    while(it.hasNext()){
        Entry pairs = (Entry)it.next();
        Class<?> c = this.getClass();
        try {
            Field value = c.getDeclaredField((String) pairs.getKey());
            value.set(this, pairs.getValue());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

answered Apr 16, 2013 at 18:45

zurbergram

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