java(format): Data Parsing Basics

Organized information on various data transformations in Java.

Outline

• String -> Number
• Date String -> Date Format
• Object -> DTO
• Entity -> DTO

String -> Number

Use parseInt and parseDouble methods to convert strings to numbers.

public class ParseInt {
    public static void main(String[] args) {
        int x = Integer.parse

```java
        int x = Integer.parseInt("12");
        double c = Double.parseDouble("12");
        int b = Integer.parseInt("100", 2);

        System.out.println(x);           // 12
        System.out.println(c);           // 12.0
        System.out.println(b);           // 4
        System.out.println(Integer.parseInt("101", 8)); // 65
    }
}

Output:

12
12.0
4
65

Date String -> Date Format

Convert date strings to Date objects using SimpleDateFormat and ParsePosition.

import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Date;

public class LocaleDateFormat {
    public static void main(String[] args) {
        SimpleDateFormat sdf1 = new SimpleDateFormat("MM/dd/yyyy");
        SimpleDateFormat sdf2 = new SimpleDateFormat("dd/MM/yyyy");

        Date date1 = sdf1.parse("10/14/2020");
        System.out.println(date1); // Wed Oct 14 00:00:00 EEST 2020

        Date date2 = sdf2.parse("14/10/2020");
        System.out.println(date2); // Wed Oct 14 00:00:00 EEST 2020

        String myString = "here is the date: 14/10/2020";
        ParsePosition p1 = new ParsePosition(18);
        Date date3 = sdf2.parse(myString, p1);
        System.out.println(date3); // Wed Oct 14 00:00:00 EEST 2020
    }
}

Output:

Wed Oct 14 00:00:00 EEST 2020
Wed Oct 14 00:00:00 EEST 2020
Wed Oct 14 00:00:00 EEST 2020

Object -> DTO

Convert an object to a Data Transfer Object (DTO) using BeanUtils.

import org.springframework.beans.BeanUtils;

public class DTOConverter {
    public static DataDto objectToDataDto(Object dtoObject) {
        DataDto dataDto = new DataDto();
        BeanUtils.copyProperties(dtoObject, dataDto);
        return dataDto;
    }
}

Entity -> DTO

Use MapStruct for converting an entity to a DTO.

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.factory.Mappers;

@Mapper
public interface CarMapper {
    CarMapper INSTANCE = Mappers.getMapper(CarMapper.class);

    @Mapping(source = "numberOfSeats", target = "seatCount")
    CarDto carToCarDto(Car car);
}

References

• Parse Methods in Java
• MapStruct
•