How to find files that match a wildcard string in Java?

java

file-manipulation

directory-stream

fileutils

byAlex Kataev·Dec 3, 2024

To locate files matching a wildcard pattern like *.txt expediently in Java, leverage the Files.newDirectoryStream method from java.nio.file. Here's a snippet:

Path dir = Paths.get("your_directory");
String pattern = "*.txt"; // Replace with your pattern.
try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, pattern)) {
    for (Path file : stream) {
        System.out.println(file.getFileName()); // Sending out a ping!
    }
} catch (IOException e) {
    // Houston, we had a problem here!
}

Replace "your_directory" with your target directory and "*.txt" with the specific wildcard to filter and print filenames.

Using alternative libraries

If the DirectoryStream isn't enough, the Apache Commons IO library offers powerful utilities for file manipulation. In particular, FileUtils and WildcardFileFilter.

For instance, if you want to dig through nested directories, like a mole:

File dir = new File("."); // Let's start digging from here.
FileFilter fileFilter = new WildcardFileFilter("*.txt"); // Our map to the treasure.
Iterator<File> files = FileUtils.iterateFiles(dir, fileFilter, TrueFileFilter.INSTANCE);  // Fun fact: A group of moles is called a "labour". 
files.forEachRemaining(file -> System.out.println(file.getName())); // Gotcha!

For complex regex patterns, the RegexFileFilter is your secret weapon:

FileFilter regexFilter = new RegexFileFilter(".*\\.txt"); // The secret weapon.
File[] files = dir.listFiles(regexFilter); // Ready, aim, fire!
for (File file : files) {
    System.out.println(file.getName()); // Bull's eye!
}

Merging modern Java features

Java 7 and 8 aren't just about fancy lambdas, they offer potent file operation tools in the form of java.nio.file and Stream API.

Harnessing Java NIO

Use PathMatcher from Java 7 with Files.newDirectoryStream to graciously handle glob patterns with royalty elegance.

FileSystem fs = FileSystems.getDefault(); 
PathMatcher matcher = fs.getPathMatcher("glob:**/*.txt"); // The royal decree!
try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
    stream.forEach(path -> {
        if (matcher.matches(path)) {
            System.out.println(path); // Loyal subjects!
        }
    });
}

Opt for Java 8 Stream

With Java 8's Files.find method coupled with lambda expressions, less is more!

Files.find(Paths.get("."), Integer.MAX_VALUE,
        (filePath, fileAttr) -> fileAttr.isRegularFile() && filePath.toString().endsWith(".txt")) // Cuts through directories like a hot knife through butter.
        .forEach(System.out::println); // Showtime!

Edge case management

At times, you might stumble upon some knightly challenges. No worries, here's how to tackle them:

Case sensitivity control

Does your file system consider File.TXT identical to file.txt? Keep an eye on case-sensitivity!

Making peace with IOExceptions

IOExceptions are part and parcel of file operations. Be ready with your try-with-resources shield or make peace with them by catching.

Jar file scouring

Is your wildcard pattern hiding in a jar file? Employ JarFile and arm yourself with the right filters.

Venture with ant.jar

Ever tried ant.jar? It’s known for its knightly charm in file search operations:

DirectoryScanner scanner = new DirectoryScanner();
scanner.setIncludes(new String[]{"**/*.java"});
scanner.setBasedir(new File("."));
scanner.setCaseSensitive(false); // It doesn't matter if you shout or whisper.
scanner.scan();
String[] files = scanner.getIncludedFiles();
for (String file : files) {
    System.out.println(file); // Ant, meet Java!
}