Json object to java arraylist

Question

I have pass two values from ajax to my servlet.

I used

JsonObject data = new Gson().fromJson(request.getReader(), JsonObject.class);
System.out.println(data);

and this is the output

{"0":"31/01/2017","1":"19/01/2017"}

Now I want to convert this data into a java arraylist but not really sure how.

I tried

Gson googleJson = new Gson();
JsonObject data = googleJson.fromJson(request.getReader(), JsonObject.class);
System.out.println(data);
JsonArray jsonArr = data.getAsJsonArray();
// jsonArr.

ArrayList jsonObjList = googleJson.fromJson(jsonArr, ArrayList.class);
for(int i=0; i< jsonObjList.size(); i++) {
    System.out.println(jsonObjList.get(i));
}

But got an error

java.lang.IllegalStateException: This is not a JSON Array.

Someone help me please? thanks.

you can use something like data.getAsString("0") and data.getAsString("1") because it's a JSONObject — Pavneet_Singh
– Pavneet_Singh, Commented Jan 1, 2017 at 12:05
what if the size of my data is not fixed? meaning the data can be more than 2. — user3429531
– user3429531, Commented Jan 1, 2017 at 12:07
one way is use entrySet() and fetch all keys and value as mapentry and other way is create POJO class with corresponding mapping fields mean Hashmap inside POJO — Pavneet_Singh
– Pavneet_Singh, Commented Jan 1, 2017 at 12:11
i guess there will be surely a way to make it as ArrayList , you can mention it in your question as requirement , someone will surely guide you — Pavneet_Singh
– Pavneet_Singh, Commented Jan 1, 2017 at 12:21

atiqkhaled · Accepted Answer · 2017-01-31 14:40:48Z

2

Create instance of JsonArray then add json element to that array using key.

Here is your solution :

Gson googleJson = new Gson();
JsonObject data = googleJson.fromJson(request.getReader(), JsonObject.class);
System.out.println(data);
JsonArray jsonArr = new JsonArray();

for(Entry<String, JsonElement> entry : data.entrySet()) {
    jsonArr.add(data.get(entry.getKey()));
}

ArrayList jsonObjList = googleJson.fromJson(jsonArr, ArrayList.class);
for(int i = 0; i < jsonObjList.size(); i++) {
    System.out.println(jsonObjList.get(i));
}

edited Jan 31, 2017 at 14:40

answered Jan 1, 2017 at 13:59

atiqkhaled

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ddarellis · Accepted Answer · 2017-01-01 12:24:48Z

0

For a Json to be a valid JsonArray object you should have it to a proper format. Can you change your json string return from your ajax? If yes you should change it to something like this:

Gson googleJson = new Gson();
JsonObject data = googleJson.fromJson("{test: [{\"0\":\"31/01/2017\"},{\"1\":\"19/01/2017\"}]}", JsonObject.class);
System.out.println(data);
JsonArray jsonArr = data.getAsJsonArray("test");

ArrayList jsonObjList = googleJson.fromJson(jsonArr, ArrayList.class);
for(int i=0; i< jsonObjList.size(); i++) {
    System.out.println(jsonObjList.get(i));
}

If not you should parse it by your self and convert it to everything you want.

answered Jan 1, 2017 at 12:24

ddarellis

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