Convert Json Array to normal Java list

Question

Is there a way to convert JSON Array to normal Java Array for android ListView data binding

User · Answer

x000D   x000D     private String   getStringArray JSONArray jsonArray  throws JSONException   x000D              if  jsonArray    null    x000D                  String   stringsArray   new String jsonArray length     x000D                  for  int i   0  i  lt  jsonArray length    i      x000D                      stringsArray i    jsonArray getString i   x000D                    x000D                  return stringsArray  x000D                else x000D                  return null  x000D            x000D   x000D   x000D

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I know that question is about JSONArray but here s example I ve found useful where you don t need to use JSONArray to extract objects from JSONObject   import org json simple JSONObject  import org json simple JSONValue   String jsonStr       types    1  2     JSONObject json    JSONObject  JSONValue parse jsonStr   List lt Long gt  list    List lt Long gt   json get  types    if  list    null        for  Long s   list            System out println s             Works also with array of strings

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I know that the question was for Java  But I want to share a possible solution for Kotlin because I think it is useful   With Kotlin you can write an extension function which converts a JSONArray into an native  Kotlin  array   fun JSONArray asArray    Array lt Any gt        return Array this length      this it        Now you can call asArray   directly on a JSONArray instance

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How about using java util Arrays   List lt String gt  list   Arrays asList  String   jsonArray toArray

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We can simply convert the JSON into readable string  and split it using  split  method of String class   String jsonAsString   yourJsonArray toString      we need to remove the leading and the ending quotes and square brackets jsonAsString   jsonAsString substring 2  jsonAsString length   -2     split wherever the String contains     String   jsonAsStringArray   jsonAsString split

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we starting from conversion   JSONArray -  List  lt  JSONObject       public static List lt JSONObject gt  getJSONObjectListFromJSONArray JSONArray array           throws JSONException     ArrayList lt JSONObject gt  jsonObjects   new ArrayList lt  gt       for  int i   0              i  lt   array    null   array length     0                         jsonObjects add array getJSONObject i                  return jsonObjects      next create generic version replacing array getJSONObject i    with POJO  example    public  lt T gt  static List lt T gt  getJSONObjectListFromJSONArray Class lt T gt  forClass  JSONArray array           throws JSONException     ArrayList lt Tt gt  tObjects   new ArrayList lt  gt       for  int i   0              i  lt   array    null   array length     0                         tObjects add   T  createT forClass  array getJSONObject i                   return tObjects     private static T createT Class lt T gt  forCLass  JSONObject jObject          instantiate via reflection   use constructor or whatsoever     T tObject   forClass newInstance           if not using constuctor args  fill up               return new pojo filled object     return tObject

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Maybe it s only a workaround  not very efficient  but you could do something like this   String   resultingArray   yourJSONarray join      split        Obviously you can change the     separator with anything you like  I had a JSONArray of email addresses

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Instead of using bundled-in org json library  try using Jackson or GSON  where this is a one-liner  With Jackson  f ex   List lt String gt  list   new ObjectMapper   readValue json  List class      Or for array  String   array   mapper readValue json  String   class

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ArrayList lt String gt  list   new ArrayList lt String gt          JSONArray jsonArray    JSONArray jsonObject   if  jsonArray    null        int len   jsonArray length       for  int i 0 i lt len i          list add jsonArray get i  toString

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If you don t already have a JSONArray object  call  JSONArray jsonArray   new JSONArray jsonArrayString     Then simply loop through that  building your own array  This code assumes it s an array of strings  it shouldn t be hard to modify to suit your particular array structure   List lt String gt  list   new ArrayList lt String gt     for  int i 0  i lt jsonArray length    i          list add  jsonArray getString i

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Here is a better way of doing it  if you are getting the data from API  Then PARSE the JSON and loading it onto your listview   protected void onPostExecute String result                    Log v TAG     result                     if   result equals                                Set up variables for API Call                     ArrayList lt String gt  list   new ArrayList lt String gt                          try                           JSONArray jsonArray   new JSONArray result                            for  int i   0  i  lt  jsonArray length    i                                   list add jsonArray get i  toString                                 end for                       catch  JSONException e                            Log e TAG   onPostExecute  gt  Try  gt  JSONException   gt      e                           e printStackTrace                                                adapter   new ArrayAdapter lt String gt  ListViewData this  android R layout simple list item 1  android R id text1  list                       listView setAdapter adapter                       listView setOnItemClickListener new OnItemClickListener                              Override                         public void onItemClick AdapterView lt   gt  parent  View view  int position  long id                                    ListView Clicked item index                             int itemPosition   position                                  ListView Clicked item value                             String itemValue    String  listView getItemAtPosition position                                   Show Alert                             Toast makeText  ListViewData this   Position      itemPosition      ListItem       itemValue  Toast LENGTH LONG  show                                                                           adapter notifyDataSetChanged                              adapter notifyDataSetChanged

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Using Java Streams you can just use an IntStream mapping the objects   JSONArray array   new JSONArray jsonString   List lt String gt  result   IntStream range 0  array length             mapToObj array  get           map Object  toString           collect Collectors toList

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Use can use a String   instead of an ArrayList lt String gt    It will reduce the memory overhead that an ArrayList has  Hope it helps   String   stringsArray   new String jsonArray length     for  int i   0  i  lt  jsonArray length  i          parametersArray i    parametersJSONArray getString i

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You can use a String   instead of an ArrayList lt String gt    Hope it helps      private String   getStringArray JSONArray jsonArray  throws JSONException               if  jsonArray    null                    String   stringsArray   new String jsonArray length                     for  int i   0  i  lt  jsonArray length    i                          stringsArray i    jsonArray getString i                                     return stringsArray                else                 return null

[java] Convert Json Array to normal Java list

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