import java.util.regex.*;

Pattern p = Pattern.compile("[0-9]+");
Matcher m = p.matcher("123");
boolean b = m.matches();

String str = "$1가 $2에 갑니다.";
str = str.replaceAll("\\$1", "강아지").replaceAll("\\$2", "학교");
==>
강아지가 학교에 갑니다.

//String str = "D:\\data\\iBatis\\자료\\abc.hwp";
String str = "D:/data/iBatis/자료/abc.hwp";
str = str.replaceAll("^.*[\\\\|/]([^\\\\|^/]*)$", "$1");

	public static void main(String[] args) {
		String str = "2018-10-04T20:38:05.000";
		Pattern pattern = Pattern.compile("(\\d\\d\\d\\d)-(\\d\\d)-(\\d\\d)T(\\d\\d):(\\d\\d):(\\d\\d).\\d\\d\\d");
		Matcher matcher = pattern.matcher(str);
		System.out.println(matcher.groupCount());
		if (matcher.find()) {
			System.out.println(matcher.group(1));
			System.out.println(matcher.group(2));
			System.out.println(matcher.group(3));
			System.out.println(matcher.group(4));
			System.out.println(matcher.group(5));
			System.out.println(matcher.group(6));
		}
	}

6
2018
10
04
20
38
05