Adding an existing json string with Gson

Question

I have a String object containing some arbitrary json. I want to wrap it inside another json object, like this:

{
   version: 1,
   content: >>arbitrary_json_string_object<<
}

How can I reliably add my json string as an attribute to it without having to build it manually (ie avoiding tedious string concatenation)?

class Wrapper {
   int version = 1;
}

gson.toJson(new Wrapper())
// Then what?

Note that the added json should not be escaped, but a be part of the wrapper as a valid json entity, like this:

{
   version: 1,
   content: ["the content", {name:"from the String"}, "object"]
}

given

String arbitraryJson = "[\"the content\", {name:\"from the String\"}, \"object\"]";

Have you tried adding a content String field? I'm curious to see the result. — everag
– everag, Commented Dec 11, 2013 at 15:09

Community · Accepted Answer · 2017-05-23 11:46:50Z

19

For those venturing on this topic, consider this.

A a = getYourAInstanceHere();
Gson gson = new Gson();
JsonElement jsonElement = gson.toJsonTree(a);
jsonElement.getAsJsonObject().addProperty("url_to_user", url);
return gson.toJson(jsonElement);

edited May 23, 2017 at 11:46

CommunityBot

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answered Nov 9, 2014 at 6:45

T.K.

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1 Comment

Sava Dimitrijević Over a year ago

This should be accepted answer! Also, if you wish to add a custom object make another JsonElement like JsonElement jsonElement2 = gson.toJsonTree(b); and add to the existing one, using: jsonElement.getAsJsonObject().add("other", jsonElement2);

Sotirios Delimanolis · Accepted Answer · 2013-12-11 15:13:37Z

8

Simple, convert your bean to a JsonObject and add a property.

Gson gson = new Gson();
JsonObject object = (JsonObject) gson.toJsonTree(new Wrapper());
object.addProperty("content", "arbitrary_json_string");
System.out.println(object);

prints

{"version":1,"content":"arbitrary_json_string"}

answered Dec 11, 2013 at 15:13

Sotirios Delimanolis

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2 Comments

user1907906 Over a year ago

Does this work if the "arbitrary_json_string" is a JSON object?

Sotirios Delimanolis Over a year ago

@LutzHorn You can use JsonObject#add(JsonElement) for that.

giampaolo · Accepted Answer · 2013-12-12 06:24:46Z

6

This is my solution:

  Gson gson = new Gson();
  Object object = gson.fromJson(arbitraryJson, Object.class);

  Wrapper w = new Wrapper();
  w.content = object;

  System.out.println(gson.toJson(w));

where I changed your Wrapper class in:

// setter and getters omitted
public class Wrapper {
  public int version = 1;
  public Object content;
}

You can also write a custom serializer for your Wrapper if you want to hide the details of the deserialization/serialization.

answered Dec 12, 2013 at 6:24

giampaolo

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Comments

jwueller · Accepted Answer · 2013-12-11 15:21:59Z

2

You will need to deserialize it first, then add it to your structure and re-serialize the whole thing. Otherwise, the wrapper will just contain the wrapped JSON in a fully escaped string.

This is assuming you have the following in a string:

{"foo": "bar"}

and want it wrapped in your Wrapper object, resulting in a JSON that looks like this:

{
    "version": 1,
    "content": {"foo": "bar"}
}

If you did not deserialize first, it would result in the following:

{
    "version": 1,
    "content": "{\"foo\": \"bar\"}"
}

edited Dec 11, 2013 at 15:21

answered Dec 11, 2013 at 15:11

jwueller

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2 Comments

Sotirios Delimanolis Over a year ago

No, you won't have to. You can use the intermediary JsonObject that uses a LinkedTreeMap underneath.

jwueller Over a year ago

@SotiriosDelimanolis: I do not think that does what I think OP is trying to achieve. I edited my answer to make my intentions more obvious.

everag · Accepted Answer · 2013-12-11 15:14:40Z

1

If you don't care about the whole JSON structure, you don't need to use a wrapper. You can deserialize it to a generic json object, and also add new elements after that.

JsonParser parser = new JsonParser();
JsonObject obj = parser.parse(jsonStr).getAsJsonObject();
obj.get("version"); // Version field

answered Dec 11, 2013 at 15:14

everag

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