Java Language Migrating from java.io.File to Java 7 NIO (java.nio.file.Path)


Example

These examples assume that you already know what Java 7's NIO is in general, and you are used to writing code using java.io.File. Use these examples as a means to quickly find more NIO-centric documentation for migrating.

There is much more to Java 7's NIO such as memory-mapped files or opening a ZIP or JAR file using FileSystem. These examples will only cover a limited number of basic use cases.

As a basic rule, if you are used to perform a file system read/write operation using a java.io.File instance method, you will find it as a static method within java.nio.file.Files.

Point to a path

// -> IO
File file = new File("io.txt");

// -> NIO
Path path = Paths.get("nio.txt");

Paths relative to another path

// Forward slashes can be used in place of backslashes even on a Windows operating system
// -> IO
File folder = new File("C:/");
File fileInFolder = new File(folder, "io.txt");

// -> NIO
Path directory = Paths.get("C:/");
Path pathInDirectory = directory.resolve("nio.txt");

Converting File from/to Path for use with libraries

// -> IO to NIO
Path pathFromFile = new File("io.txt").toPath();

// -> NIO to IO
File fileFromPath = Paths.get("nio.txt").toFile();

Check if the file exists and delete it if it does

// -> IO
if (file.exists()) {
    boolean deleted = file.delete();
    if (!deleted) {
        throw new IOException("Unable to delete file");
    }
}

// -> NIO
Files.deleteIfExists(path);

Write to a file via an OutputStream

There are several ways to write and read from a file using NIO for different performance and memory constraints, readability and use cases, such as FileChannel, Files.write(Path path, byte\[\] bytes, OpenOption... options)... In this example, only OutputStream is covered, but you are strongly encouraged to learn about memory-mapped files and the various static methods available in java.nio.file.Files.

List<String> lines = Arrays.asList(
        String.valueOf(Calendar.getInstance().getTimeInMillis()),
        "line one",
        "line two");

// -> IO
if (file.exists()) {
    // Note: Not atomic
    throw new IOException("File already exists");
}
try (FileOutputStream outputStream = new FileOutputStream(file)) {
    for (String line : lines) {
        outputStream.write((line + System.lineSeparator()).getBytes(StandardCharsets.UTF_8));
    }
}

// -> NIO
try (OutputStream outputStream = Files.newOutputStream(path, StandardOpenOption.CREATE_NEW)) {
    for (String line : lines) {
        outputStream.write((line + System.lineSeparator()).getBytes(StandardCharsets.UTF_8));
    }
}

Iterating on each file within a folder

// -> IO
for (File selectedFile : folder.listFiles()) {
    // Note: Depending on the number of files in the directory folder.listFiles() may take a long time to return
    System.out.println((selectedFile.isDirectory() ? "d" : "f") + " " + selectedFile.getAbsolutePath());
}

// -> NIO
Files.walkFileTree(directory, EnumSet.noneOf(FileVisitOption.class), 1, new SimpleFileVisitor<Path>() {
    @Override
    public FileVisitResult preVisitDirectory(Path selectedPath, BasicFileAttributes attrs) throws IOException {
        System.out.println("d " + selectedPath.toAbsolutePath());
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFile(Path selectedPath, BasicFileAttributes attrs) throws IOException {
        System.out.println("f " + selectedPath.toAbsolutePath());
        return FileVisitResult.CONTINUE;
    }
});

Recursive folder iteration

// -> IO
recurseFolder(folder);

// -> NIO
// Note: Symbolic links are NOT followed unless explicitly passed as an argument to Files.walkFileTree
Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
    @Override
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
        System.out.println("d " + selectedPath.toAbsolutePath());
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFile(Path selectedPath, BasicFileAttributes attrs) throws IOException {
        System.out.println("f " + selectedPath.toAbsolutePath());
        return FileVisitResult.CONTINUE;
    }
});


private static void recurseFolder(File folder) {
    for (File selectedFile : folder.listFiles()) {
        System.out.println((selectedFile.isDirectory() ? "d" : "f") + " " + selectedFile.getAbsolutePath());
        if (selectedFile.isDirectory()) {
            // Note: Symbolic links are followed
            recurseFolder(selectedFile);
        }
    }
}