Parsing JsonObject to List<Map<String, Object>> using Gson?

Question

I'm trying to parse a string representation of a JSON object into a List of maps. The json object will be structured something like the following:

[
 {       
  "first_name": "fname1",
  "last_name": "lname1"
 },
 {
  "first_name": "fname2",
   "last_name": "lname2"
 }
 .
 .
 .
]

The only thing that is known is the strings values (e.g "first_name", "last_name") on runtime only, therefore I cannot create any predefined classes (like usually used in fromJson() method).

I have tried to create the following function (after I saw some examples online) and it didn't work:

public List<Map<String, Object>> fromJson(String jsonAsString) {
    final JsonElement jsonElement = this.jsonParser.parse(jsonAsString);

    List<Map<String, Object>> myList= new ArrayList<Map<String, Object>>();
    Type listType = TypeToken.get(myList.getClass()).getType();
    myList= (new Gson()).fromJson(jsonElement, listType);

    return myList;
}

The result of this function is a list (length == 2 in the above case) but instead of 2 maps i'm getting 2 Objects.

Any help? Thanks!

CommonsWare · Accepted Answer · 2017-12-10 16:46:05Z

3

I don't quite understand your use of TypeToken.

The point of TypeToken is to capture parameterized type (such as List<...>) by creating anonymous class that extends generic supertype parameterized by the type you want to capture, using the following syntax:

new TypeToken<... type you want to capture ...>() {}.getType()

In your case it should be used as follows:

myList = new Gson().fromJson(jsonAsString, 
    new TypeToken<List<Map<String, Object>>>() {}.getType());

edited Dec 10, 2017 at 16:46

CommonsWare

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answered Dec 3, 2012 at 15:34

axtavt

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Comments

minus · Accepted Answer · 2012-12-03 15:38:44Z

0

You cannot use generics like that, at runtime List<Map<String, Object>> myList is the same as List<Object> myList.

You can try with an array of maps

    Gson gson = new Gson();
    Map[] x = new Map[0];
    Map[] fromJson = gson.fromJson("[\r\n" + 
            " {       \r\n" + 
            "  \"first_name\": \"fname1\",\r\n" + 
            "  \"last_name\": \"lname1\"\r\n" + 
            " },\r\n" + 
            " {\r\n" + 
            "  \"first_name\": \"fname2\",\r\n" + 
            "   \"last_name\": \"lname2\"\r\n" + 
            " }]",x.getClass());

answered Dec 3, 2012 at 15:38

minus

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