Java NIO and NIO.2

Java NIO (New I/O) was introduced in Java 1.4, and later enhanced as NIO.2 in Java 7. It provides faster, scalable, non-blocking I/O and a modern file API compared to traditional java.io.

What is Java NIO?

Java NIO (New I/O) was introduced in Java 1.4 to overcome the limitations of traditional Java I/O (streams). It provides faster, non-blocking, and buffer-oriented data processing.

Why NIO?

• Non-blocking I/O
• Efficient for large files
• Uses Channels + Buffers (faster than Streams)
• Supports memory-mapped files
• Better file operations

Core Components of NIO

A) Buffer

• Temporary memory block used to read/write data.
• Types: ByteBuffer, CharBuffer, IntBuffer, etc.

B) Channel

• A bidirectional communication channel.
• Reads/writes data from/to Buffers.
• Types:
  • FileChannel
  • SocketChannel
  • ServerSocketChannel
  • DatagramChannel

C) Selector

• Used for non-blocking multiplexed I/O.
• Single thread can manage multiple channels.

FileChannel Example (Read File)

FileInputStream fis = new FileInputStream("data.txt");
FileChannel channel = fis.getChannel();

ByteBuffer buffer = ByteBuffer.allocate(1024);
channel.read(buffer);

buffer.flip();
while (buffer.hasRemaining()) {
    System.out.print((char) buffer.get());
}

channel.close();
fis.close();

Memory-Mapped Files (Super Fast File Access)

RandomAccessFile file = new RandomAccessFile("data.txt", "r");
FileChannel channel = file.getChannel();

MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());

while (buffer.hasRemaining()) {
    System.out.print((char) buffer.get());
}

Java NIO.2 (Java 7+)

NIO.2 is an upgraded version introduced in Java 7, primarily for file handling, directories, and file system operations.

Key NIO.2 Components

A) Path Interface

Represents a file path.

Path path = Paths.get("files/data.txt");

B) Files Class

Contains 100+ utility methods for file operations:

• read / write
• create / delete
• move / copy
• check existence
• get file properties

Common Files Class Operations

Check file exists

Files.exists(path);

Read all lines

List<String> lines = Files.readAllLines(path);

Write to file

Files.write(path, "Hello Java".getBytes());

Copy file

Files.copy(source, destination, StandardCopyOption.REPLACE_EXISTING);

Move file

Files.move(oldPath, newPath);

Delete file

Files.delete(path);

Directory Stream Example

Path dir = Paths.get("logs");
try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
    for (Path file : stream) {
        System.out.println(file.getFileName());
    }
}

Walking File Tree (Search / Operations on All Files)

Files.walk(Paths.get("src"))
     .forEach(System.out::println);

WatchService (Folder Monitoring)

Used to detect:

• file creation
• modification
• deletion

WatchService watchService = FileSystems.getDefault().newWatchService();
Path path = Paths.get("data");

path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);

WatchKey key = watchService.take();
for (WatchEvent<?> event : key.pollEvents()) {
    System.out.println("New File: " + event.context());
}

Difference Between Java NIO and NIO.2