java.nio

About

The java.nio (New I/O) package, introduced in Java 1.4, provides a more efficient, buffer-oriented, and channel-based approach to I/O operations compared to the traditional stream-based I/O (java.io). It was designed for high-performance, scalable I/O, particularly for applications such as servers, networked services, and file-processing systems.

Key features of java.nio include:

• Buffers for storing and manipulating data.

• Channels for reading/writing data asynchronously or synchronously.

• Selectors for non-blocking multiplexed I/O.

• Memory-mapped files for high-speed file access.

• Charset and encoding/decoding support.

It emphasizes non-blocking I/O, where threads can perform useful work instead of waiting for I/O operations to complete.

Key Classes and Interfaces

1. Buffer Classes

Buffers are containers for data, supporting relative and absolute get/put operations.

• Buffer (abstract class) – Base class for all buffers, with properties like capacity, position, limit, and mark.

• ByteBuffer – Stores bytes; can be direct (allocated outside the heap for faster I/O) or non-direct.

• CharBuffer – Stores characters (UTF-16).

• ShortBuffer – Stores short integers.

• IntBuffer – Stores integers.

• LongBuffer – Stores long integers.

• FloatBuffer – Stores floats.

• DoubleBuffer – Stores doubles.

• MappedByteBuffer – A special ByteBuffer for memory-mapped file regions.

2. Channel Classes and Interfaces

Channels connect I/O sources/sinks to buffers.

• ReadableByteChannel – Interface for channels that can read data into buffers.

• WritableByteChannel – Interface for channels that can write data from buffers.

• FileChannel – Reads/writes from files, supports memory-mapping.

• SocketChannel – For TCP socket connections.

• ServerSocketChannel – For listening to incoming TCP connections.

• DatagramChannel – For UDP connections.

• Pipe – Two-way communication channel between threads.

3. Selector and SelectionKey

Used for non-blocking multiplexed I/O.

• Selector – Monitors multiple channels for events (read, write, accept, connect).

• SelectionKey – Represents the registration of a channel with a selector, holding interest and ready-operation sets.

4. Charset and Encoding Utilities

For handling text encoding/decoding.

• Charset – Represents a character set.

• CharsetEncoder – Encodes characters into bytes.

• CharsetDecoder – Decodes bytes into characters.

5. Other Utilities

• ByteOrder – Represents the byte order (endianness) used by buffers (BIG_ENDIAN or LITTLE_ENDIAN).

• BufferOverflowException / BufferUnderflowException – Exceptions for buffer boundary errors.

• InvalidMarkException – Exception for invalid buffer mark usage.