How to convert list data into json in java

Question

I have a function which is returning Data as List in java class  Now as per my need  I have to convert it into Json Format   Below is my function code snippet   public static List lt Product gt  getCartList         List lt Product gt  cartList   new Vector lt Product gt  cartMap keySet   size         for Product p   cartMap keySet              cartList add p             return cartList      I tried To convert into json by using this code but it is giving type mismatch error as function is of type List     public static List lt Product gt  getCartList         List lt Product gt  cartList   new Vector lt Product gt  cartMap keySet   size         for Product p   cartMap keySet              cartList add p              Gson gson   new Gson            convert your list to json      String jsonCartList   gson toJson cartList           print your generated json      System out println  jsonCartList      jsonCartList         return jsonCartList               Please help me resolve this

User · Answer

Try these simple steps   ObjectMapper mapper   new ObjectMapper    String newJsonData   mapper writeValueAsString cartList   return newJsonData  ObjectMapper   is com fasterxml jackson databind ObjectMapper ObjectMapper

User · Answer

public static List lt Product gt  getCartList          JSONObject responseDetailsJson   new JSONObject        JSONArray jsonArray   new JSONArray         List lt Product gt  cartList   new Vector lt Product gt  cartMap keySet   size         for Product p   cartMap keySet              cartList add p           JSONObject formDetailsJson   new JSONObject            formDetailsJson put  id    1            formDetailsJson put  name    name1           jsonArray add formDetailsJson             responseDetailsJson put  forms   jsonArray    Here you can see the data in json format      return cartList       you can get the data in the following form         forms                id    1    name    name1                id    2    name    name2

User · Answer

i wrote my own function to return list of object for populate combo box     public static String getJSONList java util List lt Object gt  list String kelas String name  String label            try               Object   args                 Class cl   Class forName kelas               Method getName   cl getMethod name  null               Method getLabel   cl getMethod label  null               String json                  for  int i   0  i  lt  list size    i                  Object o   list get i               if i gt 0                   json                                 json      label       getLabel invoke o args        name       getName invoke o args                       System out println  Object       i   - gt    o getNumber                               json                   return json            catch  ClassNotFoundException ex                Logger getLogger JSONHelper class getName    log Level SEVERE  null  ex             catch  Exception ex                System out println  Error in get JSON List                ex printStackTrace                      return             and call it from anywhere like     String toreturn JSONHelper getJSONList list   com bean Contact    getContactID    getNumber

User · Answer

JSONObject responseDetailsJson   new JSONObject    JSONArray jsonArray   new JSONArray     List lt String gt  ls  new  ArrayList lt String gt      for product cj cities getList          ls add cj       JSONObject formDetailsJson   new JSONObject        formDetailsJson put  id   cj id       formDetailsJson put  name   cj name       jsonArray put formDetailsJson      responseDetailsJson put  Cities   jsonArray    return responseDetailsJson

User · Answer

Using gson it is much simpler  Use following code snippet       create a new Gson instance  Gson gson   new Gson        convert your list to json  String jsonCartList   gson toJson cartList       print your generated json  System out println  jsonCartList      jsonCartList     Converting back from JSON string to your Java object      Converts JSON string into a List of Product object  Type type   new TypeToken lt List lt Product gt  gt      getType     List lt Product gt  prodList   gson fromJson jsonCartList  type        print your List lt Product gt   System out println  prodList      prodList

User · Answer

You can use the following method which uses Jackson library public static  lt T gt  List lt T gt  convertToList String jsonString  Class lt T gt  target        if StringUtils isEmpty jsonString   return List of             return new ObjectMapper   readValue jsonString  new ObjectMapper   getTypeFactory                    constructCollectionType List class  target          catch   JsonProcessingException   JSONException e            e printStackTrace            return List of

User · Answer

Try like below with Gson Library   Earlier Conversion List format were    Product  Id 1  City Bengalore  Category TV  Brand Samsung  Name Samsung LED  Type LED  Size 32 inches  Price 33500 5  Stock 17 0   Product  Id 2  City Bengalore  Category TV  Brand Samsung  Name Samsung LED  Type LED  Size 42 inches  Price 41850 0  Stock 9 0     and here the conversion source begins        Note I have created the method toString   in Product class     Creating and initializing a java util List of Product objects List lt Product gt  productList    List lt Product gt  productRepository findAll       Creating a blank List of Gson library JsonObject List lt JsonObject gt  entities   new ArrayList lt JsonObject gt        Simply printing productList size System out println  Size of productList is       productList size        Creating a Iterator for productList Iterator lt Product gt  iterator   productList iterator       Run while loop till Product Object exists  while iterator hasNext            Creating a fresh Gson Object     Gson gs   new Gson           Converting our Product Object to JsonElement        Object by passing the Product Object String value  iterator next        JsonElement element   gs fromJson  gs toJson iterator next     JsonElement class          Creating JsonObject from JsonElement     JsonObject jsonObject   element getAsJsonObject           Collecting the JsonObject to List     entities add jsonObject         Do what you want to do with Array of JsonObject System out println entities     Converted Json Result is       Id  1  City   Bengalore   Category   TV   Brand   Samsung   Name   Samsung LED   Type   LED   Size   32 inches   Price  33500 5  Stock  17 0     Id  2  City   Bengalore   Category   TV   Brand   Samsung   Name   Samsung LED   Type   LED   Size   42 inches   Price  41850 0  Stock  9 0     Hope this would help many guys

[java] How to convert list data into json in java

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