Finding Files That Match Wildcard Strings in Java

Find Files That Match Wildcard Strings in Java

Finding files that match a particular wildcard string can be a tedious and time-consuming process, particularly when you're dealing with large file systems. In Java, however, you can use powerful library classes to quickly locate files that match a given wildcard pattern. In this tutorial, we'll show you how to use the FileNameFilter class to find files that match a wildcard string in Java.

What is a Wildcard String?

A wildcard string is a special type of string that contains one or more wildcards. A wildcard can be any character that matches zero or more characters, including numbers, letters, and symbols. The most commonly used wildcards are the asterisk (*), which matches any sequence of characters, and the question mark (?), which matches any single character.

The Java FileNameFilter Class

The FileNameFilter class provides an easy way to filter out files that don't match a wildcard string. To use this class, you'll need to create a subclass that implements its accept method. This method will be invoked for each file in the directory and should return true if the file matches the filter criteria and false otherwise.

For example, if you want to filter out all files that don't have the .txt extension, you could use the following code:

class TextFileNameFilter implements FileNameFilter {
    public boolean accept(File dir, String name) {
        return name.endsWith(".txt");
    }
}

To use this filter with the File class, you can pass it as an argument to its listFiles method like this:

File dir = new File("/path/to/dir");
File[] files = dir.listFiles(new TextFileNameFilter());

This will return an array of all files in the directory that have the .txt extension.

Using Wildcards with FileNameFilter

It's not difficult to modify the above example to use wildcards. All you need to do is add logic to your implementation of the accept method to compare the filename against the wildcard pattern. This can be done using the String.matches() method like this:

class WildcardFileNameFilter implements FileNameFilter {
    private String pattern;
    
    public WildcardFileNameFilter(String pattern) {
        this.pattern = pattern;
    }
    
    public boolean accept(File dir, String name) {
        return name.matches(pattern);
    }
}

You can then use this filter by passing a wildcard pattern as an argument to its constructor:

File dir = new File("/path/to/dir");
FileNameFilter filter = new WildcardFileNameFilter("*.txt");
File[] files = dir.listFiles(filter);

This will return an array of all files that match the *.txt wildcard pattern.

Conclusion

In this tutorial, we've shown you how to use the Java FileNameFilter class to quickly find files that match wildcard strings. With the help of this class, you can easily search large directory structures for files that match a specific pattern. We hope you've found this tutorial useful and now have a better understanding of how to use wildcard strings in Java.