Gson and deserializing an array of objects with arrays in it

Question

I am trying to use Gson to deserialize a json string returned from my webservice

The structure would be returned as TypeDTO[].

where TypeDTO is like

int id;
String name;
ArrayList<ItemDTO> items[]

and ItemDTO is like

int id;
String name;
Boolean valid;

When I call the code as follows

Gson gson = new Gson();
TypeDTO[] mytypes = (TypeDTO[]) gson.fromJson(reply, TypeDTO[].class);

Everything inside the objects is null

However, If I use the

JSONArray and JSONObject to pull them out piece by piece from the org.json jars, it works fine and the fields are populated accordingly.

Any ideas as to what I'm doing wrong? is Gson extremely fast? Or am I better to stick with what I've got working already?

Thanks, David

User · Answer

Use your bean class like this  if your JSON data starts with an an array object  it helps you   Users   bean   gson fromJson response Users   class     Users is my bean class    Response is my JSON data

User · Answer

The example Java data structure in the original question does not match the description of the JSON structure in the comment   The JSON is described as       an array of  object with an array of  object       In terms of the types described in the question  the JSON translated into a Java data structure that would match the JSON structure for easy deserialization with Gson is       an array of  TypeDTO object with an array of  ItemDTO object       But the Java data structure provided in the question is not this   Instead it s       an array of  TypeDTO object with an array of an array of  ItemDTO object       A two-dimensional array    a single-dimensional array   This first example demonstrates using Gson to simply deserialize and serialize a JSON structure that is  an array of  object with an array of  object      input json Contents              id  1       name   name1        items                 id  2  name   name2   valid  true           id  3  name   name3   valid  false           id  4  name   name4   valid  true                      id  5       name   name5        items                 id  6  name   name6   valid  true           id  7  name   name7   valid  false                      id  8       name   name8        items                 id  9  name   name9   valid  true           id  10  name   name10   valid  false           id  11  name   name11   valid  false           id  12  name   name12   valid  true                Foo java   import java io FileReader  import java util ArrayList   import com google gson Gson   public class Foo     public static void main String   args  throws Exception         Gson gson   new Gson        TypeDTO   myTypes   gson fromJson new FileReader  input json    TypeDTO   class       System out println gson toJson myTypes           class TypeDTO     int id    String name    ArrayList lt ItemDTO gt  items     class ItemDTO     int id    String name    Boolean valid      This second example uses instead a JSON structure that is actually  an array of  TypeDTO object with an array of an array of  ItemDTO object    to match the originally provided Java data structure   input json Contents              id  1       name   name1        items                           id  2  name   name2   valid  true             id  3  name   name3   valid  false                             id  4  name   name4   valid  true                              id  5       name   name5        items                           id  6  name   name6   valid  true                             id  7  name   name7   valid  false                              id  8       name   name8        items                           id  9  name   name9   valid  true             id  10  name   name10   valid  false                             id  11  name   name11   valid  false             id  12  name   name12   valid  true                        Foo java   import java io FileReader  import java util ArrayList   import com google gson Gson   public class Foo     public static void main String   args  throws Exception         Gson gson   new Gson        TypeDTO   myTypes   gson fromJson new FileReader  input json    TypeDTO   class       System out println gson toJson myTypes           class TypeDTO     int id    String name    ArrayList lt ItemDTO gt  items       class ItemDTO     int id    String name    Boolean valid      Regarding the remaining two questions      is Gson extremely fast     Not compared to other deserialization serialization APIs   Gson has traditionally been amongst the slowest   The current and next releases of Gson reportedly include significant performance improvements  though I haven t looked for the latest performance test data to support those claims   That said  if Gson is fast enough for your needs  then since it makes JSON deserialization so easy  it probably makes sense to use it   If better performance is required  then Jackson might be a better choice to use   It offers much  maybe even all  of the conveniences of Gson      Or am I better to stick with what I ve got working already    I wouldn t   I would most always rather have one simple line of code like   TypeDTO   myTypes   gson fromJson new FileReader  input json    TypeDTO   class        to easily deserialize into a complex data structure  than the thirty lines of code that would otherwise be needed to map the pieces together one component at a time

[java] Gson and deserializing an array of objects with arrays in it

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