GSON - Custom Serialization and Deserialization Examples

Google GSON Tutorial

Many times, we need to write/read the JSON values which do not default representation of java object. In that case, Gson allows you to register your own custom serializer and deserializer. This is done by defining two parts:

JSON Serializers: Need to define custom serialization for an object
JSON Deserializers: Needed to define custom deserialization for a type

In our example, we will write a custom serializer and deserializer for LocalDate and LocalDateTime classes.

LocalDateSerializer
LocalDateTimeSerializer
LocalDateDeserializer
LocalDateTimeDeserializer

Check out Convert JSON to Java Object using GSON
Check out Convert Java Object to JSON using GSON

Order POJO Class - object to be serialized and deserialized

Let's first define an object to be serialized and deserialized - Order.java

class Order {
    private int id;
    private String orderName;
    private String orderDesc;
    private LocalDate orderCreatedDate;
    private LocalDateTime orderCreatedDateTime;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getOrderName() {
        return orderName;
    }

    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }

    public String getOrderDesc() {
        return orderDesc;
    }

    public void setOrderDesc(String orderDesc) {
        this.orderDesc = orderDesc;
    }

    public LocalDate getOrderCreatedDate() {
        return orderCreatedDate;
    }

    public void setOrderCreatedDate(LocalDate orderCreatedDate) {
        this.orderCreatedDate = orderCreatedDate;
    }

    public LocalDateTime getOrderCreatedDateTime() {
        return orderCreatedDateTime;
    }

    public void setOrderCreatedDateTime(LocalDateTime orderCreatedDateTime) {
        this.orderCreatedDateTime = orderCreatedDateTime;
    }

    @Override
    public String toString() {
        return "Order [id=" + id + ", orderName=" + orderName + ", orderDesc=" + orderDesc + ", orderCreatedDate=" +
            orderCreatedDate + ", orderCreatedDateTime=" + orderCreatedDateTime + "]";
    }
}

1. Custom GSON LocalDateSerializer

class LocalDateSerializer implements JsonSerializer < LocalDate > {
    private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d-MMM-yyyy");

    @Override
    public JsonElement serialize(LocalDate localDate, Type srcType, JsonSerializationContext context) {
        return new JsonPrimitive(formatter.format(localDate));
    }
}

Note that we are formatting the default local date "2018-10-26" to "27-Oct-2018".

2. Custom GSON LocalDateTimeSerializer

class LocalDateTimeSerializer implements JsonSerializer < LocalDateTime > {
    private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss");

    @Override
    public JsonElement serialize(LocalDateTime localDateTime, Type srcType, JsonSerializationContext context) {
        return new JsonPrimitive(formatter.format(localDateTime));
    }
}

Note that we are formatting the default local date "2018-10-26T11:09:05" to "27::Oct::2018 14::35::13".

3. Custom GSON LocalDateDeserializer

class LocalDateDeserializer implements JsonDeserializer < LocalDate > {
    @Override
    public LocalDate deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
    throws JsonParseException {
        return LocalDate.parse(json.getAsString(),
            DateTimeFormatter.ofPattern("d-MMM-yyyy").withLocale(Locale.ENGLISH));
    }
}

4. Custom GSON LocalDateTimeDeserializer

class LocalDateTimeDeserializer implements JsonDeserializer < LocalDateTime > {
    @Override
    public LocalDateTime deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
    throws JsonParseException {
        return LocalDateTime.parse(json.getAsString(),
            DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss").withLocale(Locale.ENGLISH));
    }
}

Register custom serializer and deserializer

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(LocalDate.class, new LocalDateSerializer());

gsonBuilder.registerTypeAdapter(LocalDateTime.class, new LocalDateTimeSerializer());

gsonBuilder.registerTypeAdapter(LocalDate.class, new LocalDateDeserializer());

gsonBuilder.registerTypeAdapter(LocalDateTime.class, new LocalDateTimeDeserializer());

Gson gson = gsonBuilder.setPrettyPrinting().create();