Implementing custom deserializer in gson using some features of default deserializer

Question

I have a JSON object which contains primitive fields like int and string and also date field and time field (also as string). Examle of my JSON:

{  
         "auditorium":"506",
         "beginLesson":"10:30",
         "date":"2016.09.12",
         "dayOfWeekString":"Monday",
         "discipline":"Math",
         "endLesson":"11:10",
         "kindOfWork":"Lesson",
         "lecturer":"John Smith"
      }

I am using GSON lib, and I am implementing custom deserializer because I want to get "beginLesson" and "endLesson" fields not as string, but as LocalTime (I am using JodaTime lib). So I get these fields and convert them to LocalTime, but I want other fields to be deserialized as normal (If I simply write fromJson() method, so every field in my class will be set as same value in json). Is there a simple way to get these fields deserialized automatically? Or the only way I have - is to write lots of lines like

MyClass.auditorium = json.get("auditorium"); MyClass.kindOfWork = json.get("kindOfWork");

Try checking here. stackoverflow.com/questions/9296427/… I'm not familiar with Gson, Jackson is my JSON library of choice. But I'm sure there is some sort of mechanism for deserializing directly to a class by passing the class object. Jackson uses annotations to mark fields for serialization. So in essense you say something like @JsonProperty("beginLesson") private LocalTime beginLessonLocalTime_; — jseashell
– jseashell, Commented Oct 24, 2016 at 19:43

notionquest · Accepted Answer · 2016-10-25 18:32:45Z

1

The LocalTime deserialization can be handled using custom TypeAdapter. Please refer LocalTimeDeserializer class.

1) Date format is set as "yyyy.MM.dd"

2) org.joda.time.LocalTime - Formatter "HH:mm"

Main Method:-

public static void main(String[] args) {
        String jsonString = "{\"auditorium\":\"506\",\"beginLesson\":\"10:30\",\"date\":\"2016.09.12\",\"dayOfWeekString\":\"Monday\",\"discipline\":\"Math\",\"endLesson\":\"11:10\",\"kindOfWork\":\"Lesson\",\"lecturer\":\"John Smith\"}";
        Gson gson = new GsonBuilder().setDateFormat("yyyy.MM.dd")
                .registerTypeAdapter(LocalTime.class, new LocalTimeDeserializer()).create();

        Auditorium auditorium = gson.fromJson(jsonString, Auditorium.class);
        System.out.println(auditorium.toString());

    }

Auditorium Class:-

public class Auditorium implements Serializable{

    private static final long serialVersionUID = 6752903482239784124L;

    private final DateTimeFormatter fmt = DateTimeFormat.forPattern("HH:mm");

    private String auditorium;
    private LocalTime beginLesson;
    private Date date;
    private String dayOfWeekString;
    private String discipline;
    private LocalTime endLesson;
    private String kindOfWork;
    private String lecturer;
    @Override
    public String toString() {
        return "Auditorium [auditorium=" + auditorium + ", beginLesson=" + beginLesson.toString(fmt) + ", date=" + date
                + ", dayOfWeekString=" + dayOfWeekString + ", discipline=" + discipline + ", endLesson=" + endLesson.toString(fmt)
                + ", kindOfWork=" + kindOfWork + ", lecturer=" + lecturer + "]";
    }

    ... getter and setters

}

LocalTime Deserializer:-

public class LocalTimeDeserializer implements JsonDeserializer<LocalTime> {

    final DateTimeFormatter fmt = DateTimeFormat.forPattern("HH:mm");

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

        return LocalTime.parse(paramJsonElement.getAsString(), fmt);
    }

}

Output:-

Auditorium [auditorium=506, beginLesson=10:30, date=Mon Sep 12 00:00:00 BST 2016, dayOfWeekString=Monday, discipline=Math, endLesson=11:10, kindOfWork=Lesson, lecturer=John Smith]

answered Oct 25, 2016 at 18:32

notionquest

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2 Comments

Leopik Over a year ago

Thank you, one more question - why you implemented Serializable in Auditorium class? This is something I should do too or it's just convinient code style for you?

notionquest Over a year ago

Refer this stackoverflow.com/questions/4548816/…. If your use case doesn't need it, you can remove the Serializable.

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