Gson deserialisation generates NULL value

Question

I was trying to read and convert a JSON file to an array but getting null values from the array after reading the JSON file. I am using the default constructor for my Ship

Answer 1

You can use something along these lines. Note that you don´t have to use Files.readAllBytes but in your code it could also be that the BufferedReader causes the error. If you need your ShipDetails as Array instead of a list, convert it or use your needed type in the TypeToken.

final GsonBuilder builder = new GsonBuilder();
final Gson gson = builder.enableComplexMapKeySerialization().create();

// you can use the buffered reader here too, but this is easier to debug if shipDetails is a file
final String jsonRepresentation = new String(Files.readAllBytes(shipDetails);

// add a type definition
final Type type = new TypeToken<ArrayList<ShipDetail>>(){}.getType();
ArrayList<ShipDetail> shipDetails = gson.fromJson(jsonRepresentation, type);

And as mentioned in the comments above, generate Getters and Setters.

Answer 2

Your Gson mapping does not match the given JSON. By default, Gson maps JSON properties to their appropriate fields in the target mapping by exact name. Take a look at:

"idmessage":"27301"

and

private String IdMessage

The property name case and the field name case do not match. What you need is map your JSON correctly. Either:

private String idmessage

or by overriding the name match (and that's more appropriate for the Java naming conventions):

@SerializedName("idmessage")
private String idMessage;

Note one field per line. This is required in order to annotated each field separately. Or, if possible, use camelCase both in Java and JSON.