Java NIO

• Java NIO (New IO) is an alternative IO API for Java.
• Java NIO offers a different IO programming model than the traditional IO APIs.
• Since Java 7.
• Java NIO enables you to do non-blocking (not fully) IO.
• Java NIO consist of the following core components:
  • Channels e.g. FileChannel, ...
  • Buffers e.g. ByteBuffer, ...
  • Selectors
• Java NIO also provides "helper" classes Paths & Files.
  • exists()
  • ...

Paths and Files

• A Java Path instance represents a path in the file system. A path can point to either a file or a directory.

• A path can be absolute or relative.

  Path path = Paths.get("c:\\\\data\\\\myfile.txt");
  

• Files class (Files) provides several static methods for manipulating files in the file system.

  static InputStream newInputStream(Path, OpenOption...) throws IOException;
  static OutputStream newOutputStream(Path, OpenOption...) throws IOException;
  static DirectoryStream<Path> newDirectoryStream(Path) throws IOException;
  static Path createFile(Path, attribute.FileAttribute<?>...) throws IOException;
  static Path createDirectory(Path, attribute.FileAttribute<?>...) throws IOException;
  static void delete(Path) throws IOException;
  static boolean deleteIfExists(Path) throws IOException;
  static Path copy(Path, Path, CopyOption...) throws IOException;
  static Path move(Path, Path, CopyOption...) throws IOException;
  static boolean isSameFile(Path, Path) throws IOException;
  static boolean isHidden(Path) throws IOException;
  static boolean isDirectory(Path, LinkOption...);
  static boolean isRegularFile(Path, LinkOption...);
  static long size(Path) throws IOException;
  static boolean exists(Path, LinkOption...);
  static boolean isReadable(Path);
  static boolean isWritable(Path);
  static boolean isExecutable(Path);
  static List<String> readAllLines(Path) throws IOException;
  static Stream<String> lines(Path) throws IOException;
  

Channels and Buffers

• All IO in NIO starts with a Channel. A Channel is similar to IO stream. From the Channel data can be read into a Buffer. Data can also be written from a Buffer into a Channel.

NIO Channels

• Java NIO Channels are similar to IO streams with a few differences:
  • You can both read and write to a Channels. Streams are typically one-way (read or write).
  • Channels can be read and written asynchronously (non-blocking).
  • Channels always read to, or write from, a Buffer.
• Channel Examples
  • FileChannel
  • DatagramChannel // UDP protocol
  • SocketChannel, ServerSocketChannel // TCP protocol

NIO Buffers

• A buffer is essentially a block of memory into which you can write data, which you can then later read again. This memory block is wrapped in a NIO Buffer object, which provides a set of methods that makes it easier to work with the memory block.
• Using a Buffer to read and write data typically follows this 4-step process:
  1. Write data into the Buffer
  2. Call buffer.flip()
  3. Read data out of the Buffer
  4. Call buffer.clear() or buffer.compact()
• Buffer Examples
  • ByteBuffer
  • CharBuffer
  • DoubleBuffer
  • FloatBuffer
  • IntBuffer
  • LongBuffer
  • ShortBuffer