Calculating calendar weeks in GWT

debug_version_with_output.java

public static String CwIso (Date inputDate) {

 String output = "Input: " + inputDate.toString() + "\r";
 Date thisThursday = new Date(inputDate.getYear(), inputDate.getMonth(), inputDate.getDate() - weekday(inputDate) + 4);
 Date firstOfJan = new Date(thisThursday.getYear(), 0, 1);

 Date firstThursdayOfYear = new Date(thisThursday.getYear(), 0, 1);
 while(weekday(firstThursdayOfYear) != 4){
 firstThursdayOfYear.setDate(firstThursdayOfYear.getDate() + 1);
 }

 Date firstMondayOfYear = new Date(firstThursdayOfYear.getYear(), 0, firstThursdayOfYear.getDate() - 3);

 Long diff = thisThursday.getTime() - firstMondayOfYear.getTime();
 Long cw = (thisThursday.getTime() - firstMondayOfYear.getTime())/1000/60/60/24/7 + 1;

 output += "This Thursday: " + df.format(thisThursday) + "\r";
 output += "First of January: " + df.format(firstOfJan) + "\r";

 output += "Diff: " + diff + "\r";
 output += "KW: " + cw + "\r";
 return output;
 }

GWT calendar week

public static Long calendarWeekIso (Date inputDate) {
 Date thisThursday = new Date(inputDate.getYear(), inputDate.getMonth(), inputDate.getDate() - weekday(inputDate) + 4);
 Date firstOfJan = new Date(thisThursday.getYear(), 0, 1);
 Date firstThursdayOfYear = new Date(thisThursday.getYear(), 0, 1);
 while(weekday(firstThursdayOfYear) != 4){
 firstThursdayOfYear.setDate(firstThursdayOfYear.getDate() + 1);
 }
 Date firstMondayOfYear = new Date(firstThursdayOfYear.getYear(), 0, firstThursdayOfYear.getDate() - 3);
 Long cw = (thisThursday.getTime() - firstMondayOfYear.getTime())/1000/60/60/24/7 + 1;
 return cw;
 }

GWT calendar weekdays

public static Integer weekday (Date date){
   int weekday = date.getDay();
   if(weekday == 0){
      weekday = 7;
   }
   return weekday;
}