java filenames filter pattern

Question

Hello, I need to implement

File[] files = getFiles( String folderName, String ptrn );

Where ptrn is a command prompt style pattern like "*2010*.txt"

I'm familar with FilenameFilter class, but can't implement public boolean accept(File dir, String filename) because String.matches() doesn't accept such patterns.

Thanks!

Answer 1

The String#matches() accepts regular expression patterns.

The regex variant of the "layman's" variant *2010*.txt would be .*2010.*\.txt.

So the following should work:

public boolean accept(File dir, String name) {
    return name.matches(".*2010.*\\.txt");
}

The double backslash is just there to represent an actual backslash because the backslash itself is an escape character in Java's String.

Alternatively, you can also do it without regex using the other String methods:

public boolean accept(File dir, String name) {
    return name.contains("2010") && name.endsWith(".txt");
}

Your best bet is likely to let ptrn represent a real regex pattern or to string-replace every . with \. and * with .* so that it becomes a valid regex pattern.

public boolean accept(File dir, String name) {
    return name.matches(ptrn.replace(".", "\\.").replace("*", ".*"));
}

Answer 2

You may need to scape your specific wild cards for those used in Java regex.

For instance to replace "*" you could use something like:

import java.io.*;

class Filter {
    public static void main ( String [] args ) {
        String argPattern = args[0];

        final String pattern = argPattern.replace(".","\\.").replace("*",".*");
        System.out.println("transformed pattern = " + pattern );
        for( File f : new File(".").listFiles( new FilenameFilter(){
                           public boolean accept( File dir, String name ) { 
                               return name.matches( pattern );
                           }
                        })){
             System.out.println( f.getName() );
        }
    }
}


$ls -l *ter.*
-rw-r--r--  1 oscarreyes  staff  1083 Jun 16 17:55 Filter.class
-rw-r--r--  1 oscarreyes  staff   616 Jun 16 17:56 Filter.java
$java Filter "*ter.*"
transformed pattern = .*ter\..*
Filter.class
Filter.java

Answer 3

I asked this question once: see http://stackoverflow.com/questions/794381/how-to-find-files-that-match-a-wildcard-string-in-java