java - Regex for date in other string -

this example string:

xzyxxy%mm%xyzxy%dd%xyyzy 

i want turn regular expression. mm has in range 1-12 , dd in range 1-31. here possible strings matches regex:

xzyxxy5xyzxy28xyyzy xzyxxy11xyzxy2xyyzy xzyxxy12xyzxy31xyyzy 

i'm new regular expression , first idea regex mm , dd , append other string. java method:

string getregex()   {      string mmregex = "";     string ddregex = "";      string regex;     regex = expression.replaceall("%dd%", ddregex);     regex = regex.replaceall("%mm%", mmregex);      return regex;  } 

the problem when find regex dd , mm , append other string doesn't work.

i think maybe want doesn't have regular expressions. if want past day , month in string, use:

string answer = string.format("xzyxxy%dxyzxy%dxyyzy", 5, 28); 

the again, if looking go other way, maybe use:

string date = "xzyxxy5xyzxy28xyyzy"; string dateparts[] = x.split("[^0-9]+"); 

then dateparts[1] "5" , dateparts[2] "28" use?