How to create java list from json using gson? Getting a NullPointerException

Question

In my Android project I'm trying to create a list of MyType using gson. For this I use the following code:

String result = "[{\"text\": \"lala\", \"created\": \"123456\"}, {\"text\": \"lele\", \"created\": \"123456\"}]";

class ReceivedMessage {
    String text;
    String created;
}

List<ReceivedMessage> receivedMessages = new Gson().fromJson(result, new TypeToken<List<ReceivedMessage>>(){}.getType());

for (ReceivedMessage mess : receivedMessages) {
    Log.wtf("This is it", mess.created);
}

Unfortunately I get a nullpointerexception. Does anybody know what I'm doing wrong here?

score 1 · Accepted Answer · answered Nov 19 '13 at 19:10

Defining the class "outside" worked pretty well:

public class ReceivedMessage {
    String text;
    String created;
}

public static void main(String[] args) {
    String result = "[{\"text\": \"lala\", \"created\": \"123456\"}, "
                    +"{\"text\": \"lele\", \"created\": \"123456\"}]";

    List<ReceivedMessage> receivedMessages = new Gson().fromJson(result,
                      new TypeToken<List<ReceivedMessage>>() {}.getType());

    for (ReceivedMessage mess : receivedMessages) {
        System.out.println("This is it " + mess.created);
    }

    ....
}

Note: Gson uses reflection and so it needs access to the class.

score 0 · Answer 2 · edited May 23 '17 at 11:50

0

Please try this :

Type listType = new TypeToken<ArrayList<ReceivedMessage>>() {}.getType();
List<ReceivedMessage> receivedMessages= new Gson().fromJson(result, listType);

Google Gson - deserialize list<class> object? (generic type)

edited May 23 '17 at 11:50

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answered Nov 19 '13 at 18:58

Eldhose M Babu

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How to create java list from json using gson? Getting a NullPointerException

2 Answers2