如何为gson方法创建对象工厂方法？

Question

I am generating a Student object from a JSON object but problem is when I create this object I also want to update its "studentClass" field. I update setStudentClass() method but I think GSON doesn't use this setter fields. How can I create a factory method for fromJson() method?

Student student = gson.fromJson(studentJSON.toString(), Student.class);
student.updateClassInfo();


public class Student{

   private String name;
   private String studentClass;

   //getters and setters

   public void updateClassInfo(){

      if(studentClass.equals("1"))
        studentClass = "starter";
      else if
      .....
   }

}

Answer 1

This requirement can be fulfilled using custom deserializer. Sample code below:-

Main method:-

public static void main(String[] args) {
        String jsonString = "{\"name\":\"John\",\"studentClass\":\"1\"}";
        //String jsonString = "{\"name\":\"John\"}";

        Gson gson = new GsonBuilder()
                .registerTypeAdapter(Student.class, new StudentModelDeserializer())
                .create();

        Student student = gson.fromJson(jsonString, Student.class);
        System.out.println(student.toString());

    }

Deserializer:-

public class StudentModelDeserializer implements JsonDeserializer<Student> {

    @Override
    public Student deserialize(JsonElement paramJsonElement, Type paramType,
            JsonDeserializationContext paramJsonDeserializationContext) throws JsonParseException {

        String studentClass = null;
        if (paramJsonElement.getAsJsonObject().get("studentClass") != null) {
            studentClass = paramJsonElement.getAsJsonObject().get("studentClass").getAsString();
        }

        Student student = new Gson().fromJson(paramJsonElement.getAsJsonObject(), Student.class);

        if (studentClass != null) {
            if (studentClass.equals("1")) {
                student.setStudentClass("starter");
            }
        }

        return student;
    }

}

Output:-

Student [name=John, studentClass=starter]

Output if student class is not present:-

Student [name=John, studentClass=null]