Skip to main content

How to convert time between timezone in Java, Primefaces?


I use the calendar Primefaces component with timeOnly and timeZone attributes for using only hour format (HH:mm). Like this:
 <p:calendar id="xabsOvertimeTimeFrom" pattern="HH:mm" timeOnly="true" value="#{data.dateFrom}" timeZone="#{data.timeZone}"/>

We can convert the value of #{data.dateFrom} from GMT/UTC time zone to local, conversely, from local time zone to GMT/UTC time zone. Here is my functions:
package vn.nvanhuong.timezoneconverter;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;



public class TimeZoneConverter {
 
 /**
  * convert a date with hour format (HH:mm) from local time zone to UTC time zone 
  */
 public static Date convertHourToUTCTimeZone(Date inputDate) throws ParseException {
  if(inputDate == null){
   return null;
  }
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(inputDate);
  int hours = calendar.get(Calendar.HOUR_OF_DAY);
  int minutes = calendar.get(Calendar.MINUTE);
  String dateString = ""+((hours>9)?""+hours:"0"+hours)+":"+((hours>9)?""+minutes:"0"+minutes)+"";
  SimpleDateFormat sdf = new SimpleDateFormat("HH:mm");
  sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
  return sdf.parse(dateString);
 }
 
 /**
  * convert a date with hour format (HH:mm) from UTC time zone to local time zone
  */
 public static Date convertHourFromUTCToLocalTimeZone(Date inputDate) throws ParseException {
  if(inputDate == null){
   return null;
  }
  Date localFromGmt = new Date(inputDate.getTime() - TimeZone.getDefault().getOffset(inputDate.getTime()));
  
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(localFromGmt);
  int hours = calendar.get(Calendar.HOUR_OF_DAY);
  int minutes = calendar.get(Calendar.MINUTE);
  String dateString = ""+((hours>9)?""+hours:"0"+hours)+":"+((hours>9)?""+minutes:"0"+minutes)+"";
  SimpleDateFormat sdf = new SimpleDateFormat("HH:mm");
  
  return sdf.parse(dateString);
 }
 
}

And Unit test for them:
package vn.nvanhuong.timezoneconverter.test;

import static org.junit.Assert.assertEquals;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

import org.junit.Test;

import vn.nvanhuong.timezoneconverter.TimeZoneConverter;

public class TimeZoneConverterTest {

 @Test
 public void testConvertHourToUTCTimeZoneWhenNull() throws ParseException {
  Date inputDate = null;
  Date expected = null;
  Date actual = TimeZoneConverter.convertHourToUTCTimeZone(inputDate); 
  assertEquals(expected,actual);
 }
 
 @Test
 public void testConvertHourToUTCTimeZoneWhenNotNull() throws ParseException {
  SimpleDateFormat isoFormat = new SimpleDateFormat("HH:mm");
  Date inputDate = isoFormat.parse("19:21");
  isoFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
  Date expected = isoFormat.parse("19:21");
  Date actual = TimeZoneConverter.convertHourToUTCTimeZone(inputDate); 
  assertEquals(expected,actual);
 }
 
 @Test
 public void testConvertHourToDefaultTimeZoneNull() throws ParseException {
  Date inputDate = null;
  Date expected = null;
  Date actual = TimeZoneConverter.convertHourFromUTCToLocalTimeZone(inputDate); 
  assertEquals(expected,actual);
 }
 
 @Test
 public void testConvertHourToDefaultTimeZoneNotNull() throws ParseException {     
  SimpleDateFormat isoFormat = new SimpleDateFormat("HH:mm");
  Date expected = isoFormat.parse("09:21");
  isoFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
  Date inputDate = isoFormat.parse("09:21"); //16:21
  Date actual = TimeZoneConverter.convertHourFromUTCToLocalTimeZone(inputDate);
  assertEquals(expected, actual);  
 }

}

Hope that is useful for everyone! ;)

Comments

Popular posts from this blog

DevOps for Dummies

Everyone talks about it, but not everyone knows what it is. Why DevOps? In general, whenever an organization adopts any new technology, methodology, or approach, that adoption has to be driven by a business need. Any kind of system that need rapid delivery of innovation requires DevOps (development and operations). Why? DevOps requires mechanisms to get fast feedback from all the stakeholders in the software application that's being delivered. DevOps approaches to reduce waste and rework and to shift resources to higher-value activities. DevOps aims to deliver value (of organization or project) faster and more efficiently. DevOps Capabilities The capabilities that make up DevOps are a broad set that span the software delivery life cycle. The following picture is a reference architecture which provides a template of a proven solution by using a set of preferred methods and capabilities. My Remarks Okay, that sounds cool. What does it simply mean, again? The f...

[Snippet] CSS - Child element overlap parent

I searched from somewhere and found that a lot of people says a basic concept for implementing this feature looks like below: HTML code: <div id="parent">  <div id="child">  </div> </div> And, CSS: #parent{   position: relative;   overflow:hidden; } #child{   position: absolute;   top: -1;   right: -1px; } However, I had a lot of grand-parents in my case and the above code didn't work. Therefore, I needed an alternative. I presumed that my app uses Boostrap and AngularJs, maybe some CSS from them affects mine. I didn't know exactly the problem, but I believed when all CSS is loaded into my browser, I could completely handle it. www.tom-collinson.com I tried to create an example to investigated this problem by Fiddle . Accidentally, I just changed: position: parent; to position: static; for one of parents -> the problem is solved. Look at my code: <div class="modal-body dn-placeholder-parent-positi...

Installing NGINX on macOS

I have heard of a lot of NGINX recently. One of them was it can help for security issues; for sure, it much be more. It so happens that our team has got a ton of user stories from a security audit. It's time to delve into it. What is NGINX? In order to get a basic idea and have some fun , I've just picked some available posts from my favorite Vietnamese blogger communities as below: https://kipalog.com/posts/Cau-hinh-nginx-co-ban---Phan-1 https://viblo.asia/hoang.thi.tuan.dung/posts/ZabG912QGzY6 NGINX (pronounce: Engine-X) is a web server (comparing to IIS, Apache). It can be used as a reverse proxy ( this is what I need for security issues with configuration ), load balancer and more. How to get started? I found the below path for learning NGINX by googling "learn nginx": https://www.quora.com/What-are-some-good-online-resources-to-learn-Nginx In this post, I only went first step. This is installing NGINX on macOS and taking a first look at the confi...

Java 8 - Persistent data structure

The following is a series of posts about "functional programming in Java" which is the result of my understanding by reading the book " Java 8 in Action: Lambdas, Streams, and Functional-style Programming, by Alan Mycroft and Mario Fusco ". 1. Why functional programming? 2. Functional programming in Java 8 3. Java 8 - Using Functions as Values 4. Java 8 - Persistent data structure Persistent data structure is also known as a simple technique but it's very important. Its other names are functional data structure and immutable data structure. Why is it "persistent"? Their values persist and are isolated from changes happening elsewhere. That's it! This technique is described as below: If you need a data structure to represent the result of a computation, you should make a new one and not mutable an existing data structure. Destructive updates version public static A doSomething(A a){ a.setProp1("new value"); return...

[Snippet] Generate a new unique "name" string from an existing list

Suppose that we have a list of employees. Everytime, we want to add new employee into this list, the name of the employee will be generated with the following rules: - the name of the new one is set to " [originalname] 1 " - in case the name already exist, " [originalname] 2 " is used, and so on. Here is my code snippet by Javascript: var employees =[ {id: 1, name: 'name'}, {id: 2, name: 'name 1'}, {id: 3, name: 'name 2'}, {id: 5, name: 'name 4'} ]; var commonUtils = { isExistName: function(_name, _collection, _prop) { for(var i = 0; i< _collection.length; i++){ if(_collection[i][_prop].localeCompare(_name)==0){ return true; } } return false; }, generateNewName: function(_name, _collection, _prop){ var i = 1; var searching = true; while (searching) { var newName = _name+ " " + i; if (!this.isExistName(newName, _collection, _pro...