Java正则表达式匹配一个反斜杠

Question

Hi I am trying to do a regular expresion that match one and only one time "\" so I can detect one directory level this example not work I don't know very regular expresion in Java.

    String  input="C:\\andres\\an";
//    String  input="C:\\andres";
    Pattern p = Pattern.compile("\\\\{1}");
    Matcher m = p.matcher(input);
    if (m.find()) {
        System.out.println("La cadena SI contiene un caracter \\");
        System.out.println(input);
    }else {
        System.out.println("La cadena no contiene un caracter \\");
        System.out.println(input);
    }
}

Answer 1

You can do this easily using a negated character class regex:

^[^\\]*\\[^\\]*$ 

In Java regex string would be:

final String regex = "^[^\\\\]*\\\\[^\\\\]*$";

RegEx Demo

RegEx Details:

• ^ : Start
• [^\\]* : Match 0 more of any characters that are not \
• \\ : Match a single \
• [^\\]* : Match 0 more of any characters that are not \
• $ : End

PS: If you're using this regex in .matches() method then anchors ^ and $ are not needed and you can just use:

final String regex = "[^\\\\]*\\\\[^\\\\]*";

Answer 2

I would use this pattern:

^(?!.*\\.*\\).*\\.*$

This regex asserts that two (or more) backslashes do not appear. Then, it goes on to match a single backslash. In Java code:

String input = "C:\\andres";
if (input.matches("(?!.*\\\\.*\\\\).*\\\\.*")) {
    System.out.println("MATCH");
}

But, String#split might offer an even easier way of doing this:

String input = "C:\\andres";
if (input.split("\\\\").length == 2) {
    System.out.println("MATCH");
}

A matching path, with only one backslash, when split on backslash should have exactly two resulting terms.