1.
String clean1 = string1.replaceAll("[^0-9]", "");
2.
String clean2 = string2.replaceAll("[^\\d]", "");
3.
String clean3 = string1.replaceAll("\\D", "");
출처 : http://stackoverflow.com/questions/6883579/java-regular-expression-removing-everything-but-numbers-from-string
+) 숫자와 . 만
String clean1 = string1.replaceAll("[^0-9.]", "");