Java正则表达式匹配两个相同的数字

Question

I want to use RE to match the file paths like below:

../90804/90804_0.jpg
../89246/89246_8.jpg
../89247/89247_14.jpg

Currently, I use the code as below to match:

Pattern r = Pattern.compile("^(.*?)[/](\\d+?)[/](\\d+?)[_](\\d+?).jpg$");
Matcher m = r.matcher(file_path);

But I found it will be an unexpected match like for:

../90804/89246_0.jpg

Is impossible in RE to match two same number?

Answer 1

You can use this regex with a capture group and back-reference of the same:

(\d+)/\1

RegEx Demo

Equivalent Java regex string will be:

final String regex = "(\\d+)/\\1";

Details:

• (\\d+) : Match 1+ digits and capture it in group #1
• / : Math literal /
• \\1 : Using back-reference #1, match same number as in group #1

Answer 2

You may use a \\2 backreference instead of the second \\d+ here:

s.matches("(.*?)/(\\d+)/(\\2)_(\\d+)\\.jpg")

See the regex demo . Note that if you use matches method, you won't need ^ and $ anchors.

Details

• (.*?) - Group 1: any 0+ chars other than line break chars as few as possible
• / - a slash
• (\\\\d+) - Group 2: one or more digits
• / - a slash
• (\\\\2) - Group 3: the same value as in Group 2
• _ - an underscore
• (\\\\d+) - Group 4: one or more digits
• \\\\.jpg - .jpg .

Java demo :

Pattern r = Pattern.compile("(.*?)/(\\d+)/(\\2)_(\\d+)\\.jpg");
Matcher m = r.matcher(file_path);
if (m.matches()) {
    System.out.println("Match found");
    System.out.println(m.group(1));
    System.out.println(m.group(2));
    System.out.println(m.group(3));
    System.out.println(m.group(4));
}

Output:

Match found
..
90804
90804
0

Answer 3

this regEx ^(.*)\\/(\\d+?)\\/(\\d+?)_(\\d+?)\\.jpg$

is matching stings like this:

../90804/90804_0.jpg
../89246/89246_8.jpg
../89247/89247_14.jpg

into 4 parts.

See example Result: