How to list all files in a directory in java

April 18, 2020
List All Files in a Directory in Java

How to list all files in a directory in Java

Say we want to get names of all the files under a directory and its subdirectories. Basically, we need to be able to look under each subdirectory and, if it has any files, add them to the result. This is a problem that can be solved recursively.
In the following section, we have two different methods doing the same thing. Example 1 creates a File object with the given path and iterates over its contents. If the content is a file, we add it to the return list.

Example 1: Get Files


public List getFiles(String path) {
    List result = new ArrayList<>();
    File root = new File(path);
    File[] filesAndDirectories = root.listFiles();

    if (filesAndDirectories != null) {
        for (var file : filesAndDirectories) {
            if (file.isFile()) {
                result.add(file.getName());
            } else if (file.isDirectory()) {
                List subResult = getFiles(file.getPath());
                result.addAll(subResult);
            }
        }
    }
    return result; 
}
In the second example, we are creating a Stream from the given path. Using functional programming (lambdas), we filter all the files from the stream and collect the file names in the returned list. We are using Files::isRegularFile method reference to invoke the static method isRegularFile.

Example 2: Get All Files Using Files.walk


public List getFiles(String path) throws IOException {
    Stream walk = Files.walk(Paths.get(path));
    List result = walk
        .filter(Files::isRegularFile)
        .map(x -> x.getFileName().toString())
        .collect(Collectors.toList());

    result.forEach(System.out::println);
    walk.close();

    return result;
}
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