GarciaPL Notes - Java and Others

Google Gson [1] is very useful library for parsing JSON to our domain object. It supports mapping JSON to such formats as Long, String, Integer, Boolean etc. The problem is when you have Timestamp [2] in your domain object. You are forced to write Adapter [3] which will help you to make it happen.

package com.garciapl.parser;


import com.google.gson.*;
import com.garciapl.model.dto.ExampleDTO;

import java.lang.reflect.Type;
import java.sql.Timestamp;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class TimestampAdapter implements JsonDeserializer {

    private final DateFormat format = new SimpleDateFormat("yyyy-MM-dd");

    @Override
    public ExampleDTO deserialize(JsonElement json, Type type, JsonDeserializationContext jsonDeserializationContext) {
        if (json.isJsonObject()) {
            JsonObject jsonObject = (JsonObject) json;
            String startDate = jsonObject.has("startDate") ? jsonObject.get("startDate").getAsString() : null;
            String endDate = jsonObject.has("endDate") ? jsonObject.get("endDate").getAsString() : null;

            Timestamp startDateStamp = null;
            Timestamp endDateStamp = null;
            if (startDate != null && endDate != null) {
                startDateStamp = createTimestamp(startDate);
                endDateStamp = createTimestamp(endDate);
            }

            return new ExampleDTO(startDateStamp, endDateStamp);
        }
        return new ExampleDTO();
    }

    private Timestamp createTimestamp(String json) {
        try {
            Date date = format.parse(json);
            return new Timestamp(date.getTime());
        } catch (ParseException e) {
            throw new JsonParseException(e);
        }
    }
}

package com.garciapl.parser;

import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.garciapl.model.dto.ExampleDTO;
import com.garciapl.util.Localization;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import java.lang.reflect.Modifier;
import java.lang.reflect.Type;

@Component
public class JsonParser {

    private final static Logger logger = LoggerFactory.getLogger(JsonParser.class);

    private Gson gson;

    public JsonParser() {
        gson = new GsonBuilder()
                .serializeNulls()
                .disableHtmlEscaping()
                .setDateFormat(Localization.BASE_DATE_FORMAT)
                .registerTypeAdapter(ExampleDTO.class, new TimestampAdapter())
                .excludeFieldsWithModifiers(Modifier.TRANSIENT)
                .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_DASHES)
                .setPrettyPrinting()
                .create();
    }

    public  T fromJson(String json, Class destinationClass) {
        if (json == null || json.isEmpty()) {
            try {
                return destinationClass.newInstance();
            } catch (InstantiationException e) {
                logger.error("JsonParser exception : ", e);
                return null;
            } catch (IllegalAccessException e) {
                logger.error("JsonParser exception : ", e);
                return null;
            }
        } else {
            return gson.fromJson(json, destinationClass);
        }
    }
}