Package java.nio.channels | Java In A Nutshell, 5th Edition

Package java.nio.channels

Java 1.4

This package is at the heart of the NIO API. A channel is a communication channel for transferring bytes from or to a java.nio.ByteBuffer . Channels serve a similar purpose to the InputStream and OutputStream classes of the java.io package, but are completely unrelated to those classes, and provide important features not available with the java.io API. The Channels class defines methods that bridge the java.io and java.nio.channels APIs, by returning channels based on streams and streams based on channels.

The Channel interface simply defines methods for testing whether a channel is open and for closing a channel. The other interfaces in the package extend Channel and define read( ) and write( ) methods for reading bytes from the channel into one or more byte buffers and for writing bytes from one or more byte buffers to the channel.

The FileChannel class defines an channel-based API for reading and writing from files (and also provides other important file functionality such as file locking and memory mapping that is not available through the java.io package). SocketChannel , ServerSocketChannel , and DatagramChannel are channels for communication over a network, and Pipe defines two inner classes that use the channel abstraction for communication between threads.

The network and pipe channels are all subclasses of the SelectableChannel class, and may be put into nonblocking mode, in which calls to read( ) and write( ) return immediately, even if the channel is not ready for reading or writing. nonblocking IO and networking is not possible using the stream abstraction of the java.io and java.net packages, and is perhaps the most important new feature of the java.nio API. The Selector class is crucial to the efficient use of nonblocking channels: it allows a program to register interested in I/O operations on several different channels at once. A call to the select( ) method of a Selector will block until one of those channels becomes ready for I/O, and will then wake up. This technique is important for writing scalable high-performance network servers. See Selector and SelectionKey for details.

Finally, this package allows for very fine-grained error handling by defining a large number of exception classes, several of which may be thrown by only a single method within the java.nio API.

Interfaces

 public interface  ByteChannel  extends ReadableByteChannel, WritableByteChannel; public interface  Channel  extends java.io.Closeable; public interface  GatheringByteChannel  extends WritableByteChannel; public interface  InterruptibleChannel  extends Channel; public interface  ReadableByteChannel  extends Channel; public interface  ScatteringByteChannel  extends ReadableByteChannel; public interface  WritableByteChannel  extends Channel;

Classes

 public final class  Channels  ; public abstract class  DatagramChannel  extends java.nio.channels.spi. AbstractSelectableChannel       implements ByteChannel, GatheringByteChannel, ScatteringByteChannel; public abstract class  FileChannel  extends java.nio.channels.spi. AbstractInterruptibleChannel       implements ByteChannel, GatheringByteChannel, ScatteringByteChannel; public static class  FileChannel.MapMode  ; public abstract class  FileLock  ; public abstract class  Pipe  ; public abstract static class  Pipe.SinkChannel  extends java.nio.channels.spi. AbstractSelectableChannel        implements GatheringByteChannel, WritableByteChannel; public abstract static class  Pipe.SourceChannel  extends java.nio.channels.spi. AbstractSelectableChannel       implements ReadableByteChannel, ScatteringByteChannel; public abstract class  SelectableChannel  extends java.nio.channels.spi. AbstractInterruptibleChannel        implements Channel; public abstract class  SelectionKey  ; public abstract class  Selector  ; public abstract class  ServerSocketChannel  extends java.nio.channels.spi. AbstractSelectableChannel; public abstract class  SocketChannel  extends java.nio.channels.spi. AbstractSelectableChannel       implements ByteChannel, GatheringByteChannel, ScatteringByteChannel;

Exceptions

 public class  AlreadyConnectedException  extends IllegalStateException; public class  CancelledKeyException  extends IllegalStateException; public class  ClosedChannelException  extends java.io.IOException;    public class  AsynchronousCloseException  extends ClosedChannelException;       public class  ClosedByInterruptException  extends AsynchronousCloseException; public class  ClosedSelectorException  extends IllegalStateException; public class  ConnectionPendingException  extends IllegalStateException; public class  FileLockInterruptionException  extends java.io.IOException; public class  IllegalBlockingModeException  extends IllegalStateException; public class  IllegalSelectorException  extends IllegalArgumentException; public class  NoConnectionPendingException  extends IllegalStateException; public class  NonReadableChannelException  extends IllegalStateException; public class  NonWritableChannelException  extends IllegalStateException; public class  NotYetBoundException  extends IllegalStateException; public class  NotYetConnectedException  extends IllegalStateException; public class  OverlappingFileLockException  extends IllegalStateException; public class  UnresolvedAddressException  extends IllegalArgumentException; public class  UnsupportedAddressTypeException  extends IllegalArgumentException;