validate date format using regex JAVA - regex-lookarounds

Question

Can we validate dd/MM/yyyy and MM/dd/yyyy format together using regex.
I want to validate any valid date format from user, I wrote regex for all other format but not able to differentiate dd/MM/yyyy and MM/dd/yyyy together.

Answer 1

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
/**
*
*/
/**
* #author Ravi Shankar
*
*/
public class DateFormater {
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
new DateFormater().dateParser("CURR-MAY");
}
public String dateParser(String paramDate){
String date=null;
DateFormat df= null;
DateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
//
if(null != paramDate && !paramDate.equalsIgnoreCase("")){
paramDate = paramDate.trim();
if(paramDate.matches("\\d{4}[/]\\d{1,2}[/]\\d{1,2}")){
df = new SimpleDateFormat("yyyy/MM/dd");
}else if(paramDate.matches("\\d{4}[-]\\d{1,2}[-]\\d{1,2}")){
df = new SimpleDateFormat("yyyy-MM-dd");
}else if(paramDate.matches("\\d{4}[.]\\d{1,2}[.]\\d{1,2}")){
df = new SimpleDateFormat("yyyy.MM.dd");
}else if(paramDate.matches("\\d{1,2}[/]\\d{1,2}[/]\\d{2}")){
df = new SimpleDateFormat("MM/dd/yy");
}else if(paramDate.matches("\\d{1,2}[-]\\d{1,2}[-]\\d{2}")){
df = new SimpleDateFormat("MM-dd-yy");
}else if(paramDate.matches("\\d{1,2}[.]\\d{1,2}[.]\\d{2}")){
df = new SimpleDateFormat("MM.dd.yy");
}else if(paramDate.matches("\\d{1,2}[/]\\d{1,2}[/]\\d{4}")){
df = new SimpleDateFormat("MM/dd/yyyy");
}else if(paramDate.matches("\\d{1,2}[-]\\d{1,2}[-]\\d{4}")){
df = new SimpleDateFormat("MM-dd-yyyy");
}else if(paramDate.matches("\\d{1,2}[.]\\d{1,2}[.]\\d{4}")){
df = new SimpleDateFormat("MM.dd.yyyy");
}else if(paramDate.matches("\\d{1,2}[/]\\d{1,2}")){
df = new SimpleDateFormat("MM/dd/yyyy");
paramDate = addYear(paramDate);
}else if(paramDate.matches("\\d{1,2}[-]\\d{1,2}")){
df = new SimpleDateFormat("MM-dd-yyyy");
paramDate = addYear(paramDate);
}else if(paramDate.matches("\\d{1,2}[.]\\d{1,2}")){
df = new SimpleDateFormat("MM.dd.yyyy");
paramDate = addYear(paramDate);
}else if(paramDate.matches("\\d{1,2}[/]\\d{4}")){
df = new SimpleDateFormat("MM/yyyy");
}else if(paramDate.matches("\\d{1,2}[-]\\d{4}")){
df = new SimpleDateFormat("MM-yyyy");
}else if(paramDate.matches("\\d{1,2}[.]\\d{4}")){
df = new SimpleDateFormat("MM.yyyy");
}else if(paramDate.matches("\\S{3}[/]\\d{2}")){
df = new SimpleDateFormat("MMM/yy");
}else if(paramDate.matches("\\S{3}[-]\\d{2}")){
df = new SimpleDateFormat("MM-yy");
}else if(paramDate.matches("\\S{3}[.]\\d{2}")){
df = new SimpleDateFormat("MM.yy");
}else if(paramDate.matches("\\d{1,2}[/]\\S{3}")){
df = new SimpleDateFormat("MM/dd/yyyy");
paramDate = addYear2(paramDate);
}else if(paramDate.matches("\\d{1,2}[-]\\S{3}")){
df = new SimpleDateFormat("MM-dd-yyyy");
paramDate = addYear2(paramDate);
}else if(paramDate.matches("\\d{1,2}[.]\\S{3}")){
df = new SimpleDateFormat("MM.dd.yyyy");
paramDate = addYear2(paramDate);
}else if(paramDate.matches("\\S{3}")){
df = new SimpleDateFormat("MM/dd/yyyy");
paramDate = addYear3(paramDate);
}else if(paramDate.matches("\\S{3,6}[-]\\S{3}")){
df = new SimpleDateFormat("MM/dd/yyyy");
paramDate = addYear3(paramDate);
}
try {
date = sdf.format(df.parse(paramDate));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return date;
}
/**
* #param paramDate
* Adding Year in MM/DD
* #return
*/
public String addYear(String paramDate){
int month = 0;
String sp= "";
if(paramDate.matches("\\d{1,2}[/]\\d{1,2}")){
month =Integer.parseInt(paramDate.split("/")[0]);
sp="/";
}else if(paramDate.matches("\\d{1,2}[-]\\d{1,2}")){
month =Integer.parseInt(paramDate.split("-")[0]);
sp="-";
}else if(paramDate.matches("\\d{1,2}[.]\\d{1,2}")){
month =Integer.parseInt(paramDate.split(".")[0]);
sp=".";
}
month =Integer.parseInt(paramDate.split("/")[0]);
Calendar cal = Calendar.getInstance();
int cm = cal.get(Calendar.MONTH) + 1;
int year = 0;
if((month - cm)>=0){
year = cal.get(Calendar.YEAR);
}else{
year = cal.get(Calendar.YEAR)+1;
}
return paramDate= paramDate+sp+year;
}
/**
* #param paramDate
* Converting dd/MMM to MM/dd and adding yyyy
* #return
*/
public String addYear2(String paramDate){
String date="";
DateFormat sdf = new SimpleDateFormat("MM/dd"); ;
DateFormat df = new SimpleDateFormat("dd/MMM"); ;
if(paramDate.matches("\\d{2}[-]\\S{3}")){
df = new SimpleDateFormat("dd-MMM");
}else if(paramDate.matches("\\d{2}[.]\\S{3}")){
df = new SimpleDateFormat("dd.MMM");
}
try {
date = addYear(sdf.format(df.parse(paramDate)));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return date;
}
/**
* #param paramDate
* converting MMM to MM/dd and adding yyyy
* #return
*/
public String addYear3(String paramDate){
String date="";
DateFormat sdf = new SimpleDateFormat("MM/dd");
DateFormat df = new SimpleDateFormat("MMM");
if(paramDate.matches("\\S{3,6}[-]\\S{3}")){
paramDate=paramDate.split("-")[1];
}
try {
date = addYear(sdf.format(df.parse(paramDate)));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return date;
}
}