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I'm assuming that you want all files that end with ".csv", correct?
The regex will match regular characters (that is, characters without a special meaning), so the end of the regex would be "csv".
A dot (.) has a special meaning so you have to escape it with a backslash (\.). But a backslash is a special character in
Java Strings, so you have to escape the backslash too: "\\.csv".
Now you want to say, "Any number of characters before the .cvs". Dot (.) matches any character, but you want one or more characters. Plus (+) means, "At least one of the things just before me," so the regex would be ".+\\.csv".
Read the Java API on java.util.regex.Pattern and java.util.regex.Matcher for more information.