Abstract class with Gson serialization/deserialization

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I am expecting to get from a json a LinkedList<Request>. The pojos look like this:

@Data
@Builder
public class Request {
    private String id;
    private List<Parameter> parameters;
}

@Data
@SuperBuilder
public abstract class Parameter implements Serializable {
    private String key;
    public abstract Object getValue();
}

@Data
@SuperBuilder
@EqualsAndHashCode(callSuper = true)
public class StringParameter extends Parameter implements Serializable {
    private String value;
}

@Data
@SuperBuilder
@EqualsAndHashCode(callSuper = true)
public class PasswordParameter extends Parameter implements Serializable {
    private String value;
}

The serialization works fine, it generates the json, but it crashes at deserialization (maybe it’s the abstract class or/and that I am expecting a LinkedList and/or the lombok annotations)? I tryed writting a gson deserializer (quite a standard one found googling), but it doesn’t do the job.

Answer

Thanks to @fluffy’s suggestion, I managed to skip writing a custom deserialiser and making use of RuntimeTypeAdapterFactory from gson-extras library:

public static void writeObjectToFile(Object object, String filePath) {
      RuntimeTypeAdapterFactory<Parameter> parameterAdapterFactory = RuntimeTypeAdapterFactory.of(Parameter.class, "type");
      parameterAdapterFactory.registerSubtype(StringParameter.class, "StringParameter");
      parameterAdapterFactory.registerSubtype(PasswordParameter.class, "PasswordParameter");
      Gson gson = new GsonBuilder().setPrettyPrinting().registerTypeAdapterFactory(parameterAdapterFactory).create();
      try {
          FileWriter fileWriter = new FileWriter(filePath);
          gson.toJson(object, fileWriter);
          fileWriter.flush();
          fileWriter.close();
      } catch (IOException e) {
          System.out.println(e.getMessage());
      }
  }

  public static LinkedList<Request> readObjectFromFile(String filePath) {
      RuntimeTypeAdapterFactory<Parameter> parameterAdapterFactory = RuntimeTypeAdapterFactory.of(Parameter.class, "type");
      parameterAdapterFactory.registerSubtype(StringParameter.class, "StringParameter");
      parameterAdapterFactory.registerSubtype(PasswordParameter.class, "PasswordParameter");
      Gson gson = new GsonBuilder().setPrettyPrinting().registerTypeAdapterFactory(parameterAdapterFactory).create();
      try {
          BufferedReader jsonBuffer = new BufferedReader(new FileReader(filePath));
          return gson.fromJson(jsonBuffer, new TypeToken<LinkedList<Request>>(){}.getType());
      } catch (FileNotFoundException e) {
          System.out.println(e.getMessage());
      }
      return  null;
  }

I also kept only the lombok annotations and did not write constructors and getters/setters for my POJOs



Source: stackoverflow