查找两个字符串之间的子字符串

Question

I have a string such as:
file = "UserTemplate324.txt"

I'd like to extract "324". How can I do this without any external libraries like Apache StringUtils?

Answer 1

Assuming you want "the digits just before the dot":

String number = str.replaceAll(".*?(\\d+)\\..*", "$1");

This uses regex to find and capture the digits and replace the entire input with them.

Of minor note is the use of a non-greedy quantifier to consume the minimum leading input (so as not to consume the leading part of the numbers too).

Answer 2

If you want to exclude the non-digit characters:

String number = file.replaceAll("\\D+", "");

\\\\D+ means a series of one or more non digit (0-9) characters and you replace any such series by "" ie nothing, which leaves the digits only.