Regex -Muster für die Datumsvalidierung
// Pattern validates that:
// day is from 01 to 31
// month is from 01 to 12
// year must be 19yy or 20yy
// delimiter is / or - or .
// date format is dd-mm-yyyy or yyyy-mm-dd
String dateRegex =
"((0[1-9]|[12][0-9]|3[01])" + //dd from 01 to 31
"[/.-]" + // - or . or /
"([01][0-9])" + //mm from 01 to 12
"[/.-]" + // - or . or /
"(19[0-9]{2}|20[0-9]{2}))" + //yyyy must be 19yy or 20yy
"|" + //or
"((19[0-9]{2}|20[0-9]{2})" + //yyyy must be 19yy or 20yy
"[/.-]" + // - or . or /
"([01][0-9])" + //mm from 01 to 12
"[/.-]" + // - or . or /
"(0[1-9]|[12][0-9]|3[01]))"; //dd from 01 to 31