java regular expression to match file path

Question

I was trying out to create a regular expression to match file path in java like

C:\abc\def\ghi\abc.txt

I tried this ([a-zA-Z]:)?(\\[a-zA-Z0-9_-]+)+\\? , like following code

import java.util.regex.Pattern;

  public class RETester {

public static void main(String arhs[]){

    String regularExpression = "([a-zA-Z]:)?(\\[a-zA-Z0-9_-]+)+\\?";

    String path = "D:\\directoryname\\testing\\abc.txt";

    Pattern pattern = Pattern.compile(regularExpression);

    boolean isMatched = Pattern.matches(regularExpression,path);
    System.out.println(path);
    System.out.println(pattern.pattern());
    System.out.println(isMatched);

}

}

However it's always giving me , false as result .

Answer 1

Java is using backslash-escaping too, you know, so you need to escape your backslashes twice, once for the Java string, and once for the regexp.

"([a-zA-Z]:)?(\\\\[a-zA-Z0-9_.-]+)+\\\\?"

Your regexp matched a literal '[-zA-Z0-9_-' string, and a literal '?' at the end. I also added a period in there to allow 'abc.txt'..

That said, consider using another mechanism for determine valid file names, as there are different schemes (i.e. unix). java.util.File will probably throw an exception if the path is invalid, which might be a good alternative, although I don't like using exceptions for control flow...

Answer 2

Use this regex:

"([a-zA-Z]:)?(\\\\[a-zA-Z0-9._-]+)+\\\\?";

I added two modifications: you forgot to add . for matching the file name abc.txt and backslash escaping (\\) was also needed.

Answer 3

Since the path contains folders and folder name can contain any character other than

? \ / : " * < >

We can use the below regex to match a directory path [it uses all the symbols that a folder name can afford]

[A-Za-z]:[A-Za-z0-9\!\@\#\$\%\^\&\(\)\'\;\{\}\[\]\=\+\-\_\~\`\.\\]+

Answer 4

It does not match, because your regex match only to paths, not to files. -- More correct: it does not accept the dot in your file name.

And in addition, there is the escaping problem mentiond by roe.

Answer 5

Just saying, one should replace the . in

([a-zA-Z]:)?(\\\\[a-zA-Z0-9_.-]+)+\\\\?

with \\.

. is meant for any character in a regular expression (Java style), while
\. is specifically meant for . character, and we need to escape the backslash

Answer 6

Here is correct regex for windows filesystem:

Regular Expression:

(?:[a-zA-Z]\:)\\([\w-]+\\)*\w([\w-.])+  

as a Java string

"(?:[a-zA-Z]\\:)\\\\([\\w-]+\\\\)*\\w([\\w-.])+"

Answer 7

If it has to match only the path of files lying on the same machine where your app is running, then you can use:

try{
    java.nio.file.Paths.get(yourPath);
}(catch InvalidPathException err){
}

So if you're running your app on windows the code above will catch invalid windows paths and if you're running on unix, it will catch invalid unix paths, etc.

Answer 8

There are two reasons why it is giving you false. First one is that you need \\\\ instead of \\ because you need to escape these characters. And the second one is that you're missing a dot character, you can insert it before a-z as ([a-zA-Z]:)?(\\\\[.a-zA-Z0-9_-]+)+\\\\?

Answer 9

A nice explanation is given here: https://www.codeproject.com/Tips/216238/Regular-Expression-to-Validate-File-Path-and-Exten

I am summarizing the same:

Regex:

^(?:[\w]\:|\\)(\\[a-z_\-\s0-9\.]+)+\.(txt|gif|pdf|doc|docx|xls|xlsx|apk)$

"^(?:[\\w]\\:|\\\\)(\\\\[a-z_\\-\\s0-9\\.]+)+\\.(txt|gif|pdf|doc|docx|xls|xlsx|apk)$"

It will work for any of these paths:

\\192.168.0.1\folder\file.pdf
\\192.168.0.1\my folder\folder.2\file.gif
c:\my folder\abc abc.docx
c:\my-folder\another_folder\abc.v2.docx