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.

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Why NIO?

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

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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.

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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();

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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());
}

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Java NIO.2 (Java 7+)

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

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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

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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);

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Directory Stream Example

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

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Walking File Tree (Search / Operations on All Files)

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

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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());
}

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Difference Between Java NIO and NIO.2

Feature	Java NIO (Java 1.4)	Java NIO.2 (Java 7)
Purpose	High-performance I/O (non-blocking, scalable)	Modern, simplified file handling and filesystem operations
Main Concept	Buffers, Channels, Selectors	Path, Paths, Files, FileVisitor, WatchService
Focus Area	Network I/O, buffer-based processing	File system operations (copy, move, delete, read, write, monitoring)
File Handling	Limited & complex using FileChannel	Very easy using Files class
Path Handling	Not available	Introduced Path interface (replaces File)
Directory Traversal	Manual, difficult	Simple with Files.walk() and FileVisitor
File Monitoring	Not supported	Supported via WatchService
Copy / Move Files	Requires manual byte operations	One line: Files.copy(), Files.move()
Delete Files	Using File API or channel workaround	Files.delete() (clean, reliable)
Exception Handling	Traditional I/O exceptions	Enhanced exceptions (e.g., FileAlreadyExistsException)
Symbolic Links	No direct support	Full support in NIO.2
Use Case	High-performance server networking	Modern file operations & directory management