How to put a List class into a JSONObject and then read that object

Question

I have a List lt class gt  that I would like to convert into a json object and then traverse the data out of the json object     If this were just a list lt String gt  I could just do something like   JSONObject obj   new JSONObject    List lt String gt  sList   new ArrayList lt String gt     sList add  val1    sList add  val2     obj put  list   sList     Then I could traverse the list like   JSONArray jArray   obj getJSONArray  list    for int ii 0  ii  lt  jArray size    ii     System out println jArray getString ii      The problem with using the class is that I need to have access to data within each class element of my list lt class gt  and I don t know how to encode that   traverse it into JSON   Any help would be greatly appreciated

User · Answer

Just to update this thread  here is how to add a list  as a json array  into JSONObject  Plz substitute YourClass with your class name   List lt YourClass gt  list   new ArrayList lt  gt     JSONObject jsonObject   new JSONObject     org codehaus jackson map ObjectMapper objectMapper   new  org codehaus jackson map ObjectMapper    org codehaus jackson JsonNode listNode   objectMapper valueToTree list   org json JSONArray request   new org json JSONArray listNode toString     jsonObject put  list   request

User · Answer

You could use a JSON serializer deserializer like flexjson to do the conversion for you

User · Answer

Call getJSONObject   instead of getString    That will give you a handle on the JSON object in the array and then you can get the property off of the object from there   For example  to get the property  value  from a List lt SomeClass gt  where SomeClass has a String getValue   and setValue String value    JSONObject obj   new JSONObject    List lt SomeClass gt  sList   new ArrayList lt SomeClass gt      SomeClass obj1   new SomeClass    obj1 setValue  val1    sList add obj1    SomeClass obj2   new SomeClass    obj2 setValue  val2    sList add obj2    obj put  list   sList    JSONArray jArray   obj getJSONArray  list    for int ii 0  ii  lt  jArray length    ii      System out println jArray getJSONObject ii  getString  value

User · Answer

Let us assume that the class is Data with two objects name and dob which are both strings      Initially  check if the list is empty  Then  add the objects from the list to a JSONArray   JSONArray allDataArray   new JSONArray    List lt Data gt  sList   new ArrayList lt String gt            if List not empty     if    sList size     0                Loop index size           for int index   0  index  lt  sList size    index                  JSONObject eachData   new JSONObject                try                   eachData put  name   sList get index  getName                     eachData put  dob   sList get index  getDob                   catch  JSONException e                    e printStackTrace                              allDataArray put eachData                   else             Do something when sList is empty            Finally  add the JSONArray to a JSONObject    JSONObject root   new JSONObject        try           root put  data   allDataArray         catch  JSONException e            e printStackTrace               You can further get this data as a String too    String jsonString   root toString

User · Answer

This is how I do it using Google Gson  I am not sure  if there are a simpler way to do this   with or without an external library     Type collectionType   new TypeToken lt List lt Class gt  gt                           end new                          getType                     String gsonString                    new Gson   toJson objList  collectionType

[java] How to put a List<class> into a JSONObject and then read that object?

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