Java RegEx找不到匹配错误

Question

Following regex giving me java.lang.IllegalStateException: No match found error

String requestpattern = "^[A-Za-z]+ \\/+(\\w+)";
Pattern p = Pattern.compile(requestpattern);
Matcher matcher = p.matcher(requeststring);
return matcher.group(1);

where request string is

POST //upload/sendData.htm HTTP/1.1

Any help would be appreciated.

Answer 1

No match has been attempted. Call find() before calling group() .

public static void main(String[] args) {
    String requeststring = "POST //upload/sendData.htm HTTP/1.1";
    String requestpattern = "^[A-Za-z]+ \\/+(\\w+)";
    Pattern p = Pattern.compile(requestpattern);
    Matcher matcher = p.matcher(requeststring);
    System.out.println(matcher.find());
    System.out.println(matcher.group(1));
}

Output:

true
upload

Answer 2

The Matcher#group(int) throws :

IllegalStateException - If no match has yet been attempted, or if the 
previous match operation failed.

Answer 3

Your expression requires one or more letters, followed by a space, followed by one or more forward slashes, followed by one or more word characters. Your test string doesn't match. The exception is triggered because you're trying to access a group on a matcher that returns no matches.

Your test string matches up to the slash after "upload", because the slash isn't matched by \\w , which only includes word characters. Word characters are letters, digits, and underscores. See: http://www.regular-expressions.info/charclass.html#shorthand