Date time processing in Java

Introduction

Date and time are interesting topics. Java provides java.time package for processing them with some classes:

• Instance: is essentially a numeric timestamp
• LocalDate: stores a date without a time. For example, this stores “2018-10-24” date.
• LocalTime stores a time without a date. For example, this store “02:30” time.
• LocalDateTime stores a date and time. For example, this stores “2018-10-24T02:30”

When working with Date and Time, we may face some problems. This guide will list and propose some approach to solve common problems in date/time process using Java.

Get current date/time

• Get current date without time

  // returns the current date from the system clock in the default time-zone.
  LocalDate.now()
  
  // get the current date from the system clock in GMT-7 time-zone
  LocalDate.now(ZoneId.of("GMT-7")
  

• Get current time without date

  // get the current time from the system clock in the default time-zone.
  LocalTime.now()
  
  // get the current time from the system clock in GMT-7 time-zone
  LocalTime.now(ZoneId.of("GMT-7")
  

• Get current date and time

  // get current date-time from the system clock in the default time-zone.
  LocalDateTime.now()
  ZonedDateTime.now()
  
  // get the current date-time from the system clock in GMT-7 time-zone
  LocalDateTime.now(ZoneId.of("GMT-7")
  ZonedDateTime.now(ZoneId.of("GMT-7")
  

• Get date/time as a single numeric value

  // return the current timein milliseconds
  // it is the number in milliseconds, between the current time and midnight, January 1, 1970 UTC.
  System.currentTimeMillis()
  

Parse string to date time

• Date format pattern

  // Date format pattern
  String stringDate = "October 26, 2018";
  DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.ENGLISH);
  LocalDate date = LocalDate.parse(stringDate, dateTimeFormatter);
  System.out.println(date); // 2018-10-26
  

• Time format pattern

  // Time format pattern
  String stringTime = "22:30:10";
  DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("H:m:s", Locale.ENGLISH);
  LocalTime time = LocalTime.parse(stringTime, timeFormatter);
  System.out.println(time); // 22:30:10
  

• DateTime format pattern

  // DateTime format pattern
  String strDateTime = "October 26, 2018 22:30:10";
  DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("MMMM d, yyyy H:m:s", Locale.ENGLISH);
  LocalDateTime dateTime = LocalDateTime.parse(strDateTime, dateTimeFormatter);
  System.out.println(dateTime);   // 2018-10-26T22:30:10
  

List of all patterns for formatting and parsing from Java doc:

Compare Date/Time

    LocalDateTime dateTime1 = LocalDateTime.parse("2018-10-26T09:30:10");
    LocalDateTime dateTime2 = LocalDateTime.parse("2018-10-30T09:30:10");

    System.out.println(dateTime1.isAfter(dateTime2));   // false
    System.out.println(dateTime1.isBefore(dateTime2));  // true
    System.out.println(dateTime1.compareTo(dateTime2)); // -4
    System.out.println(dateTime2.compareTo(dateTime1)); // 4

    LocalDateTime dateTime3 = LocalDateTime.parse("2018-11-01T05:30:10");
    // Check if dateTime2 is between dateTime1 and dateTime3
    // dateTime1 <= dateTime2 <= dateTime3
    boolean isBetween = !dateTime2.isBefore(dateTime1) && !dateTime2.isAfter(dateTime3);
    System.out.println(isBetween);  // true

Sample source code

package com.newbedev.time;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class DateTimeExample {
    public static void main(String[] args) {
        getCurrentDateTime();
        parseString2DateTime();
        compareDateTime();
    }


    private static void getCurrentDateTime() {
        System.out.println("Get current date/time:");
        System.out.println(LocalDate.now());
        System.out.println(LocalDate.now(ZoneId.of("GMT-7")));

        System.out.println(LocalTime.now());
        System.out.println(LocalTime.now(ZoneId.of("GMT-7")));

        System.out.println(LocalDateTime.now());
        System.out.println(LocalDateTime.now(ZoneId.of("GMT-7")));

        System.out.println(ZonedDateTime.now());
        System.out.println(ZonedDateTime.now(ZoneId.of("GMT-7")));
        System.out.println();
    }

    private static void parseString2DateTime() {
        System.out.println("Parse string to date/time");
        // Date format pattern
        String stringDate = "October 26, 2018";
        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("MMMM d, yyyy", Locale.ENGLISH);
        LocalDate date = LocalDate.parse(stringDate, dateFormatter);
        System.out.println(date);   // 2018-10-26

        // Time format pattern
        String stringTime = "22:30:10";
        DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("H:m:s", Locale.ENGLISH);
        LocalTime time = LocalTime.parse(stringTime, timeFormatter);
        System.out.println(time);   // 22:30:10

        // DateTime format pattern
        String strDateTime = "October 26, 2018 22:30:10";
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("MMMM d, yyyy H:m:s", Locale.ENGLISH);
        LocalDateTime dateTime = LocalDateTime.parse(strDateTime, dateTimeFormatter);
        System.out.println(dateTime);   // 2018-10-26T22:30:10
        System.out.println();
    }

    private static void compareDateTime() {
        System.out.println("Compare date/time");
        LocalDateTime dateTime1 = LocalDateTime.parse("2018-10-26T09:30:10");
        LocalDateTime dateTime2 = LocalDateTime.parse("2018-10-30T09:30:10");

        System.out.println(dateTime1.isAfter(dateTime2));   // false
        System.out.println(dateTime1.isBefore(dateTime2));  // true
        System.out.println(dateTime1.compareTo(dateTime2)); // -4
        System.out.println(dateTime2.compareTo(dateTime1)); // 4

        LocalDateTime dateTime3 = LocalDateTime.parse("2018-11-01T05:30:10");
        // Check if dateTime2 is between dateTime1 and dateTime3
        // dateTime1 <= dateTime2 <= dateTime3
        boolean isBetween = !dateTime2.isBefore(dateTime1) && !dateTime2.isAfter(dateTime3);
        System.out.println(isBetween);  // true
        System.out.println();
    }
}