Editing Non-blocking I/O (Java) (section)

===Channels===
Channels ([[Object (computer science)|classes]] implementing the interface {{Javadoc:SE|package=java.nio.channels|java/nio/channels|Channel}}) are designed to provide for bulk data transfers to and from NIO buffers.  This is a low-level data transfer mechanism that exists in parallel with the classes of the higher-level I/O library (packages {{Javadoc:SE|package=java.io|java/io}} and {{Javadoc:SE|package=java.net|java/net}}).  A channel implementation can be obtained from a high-level data transfer class such as {{Javadoc:SE|package=java.io|java/io|File}}, {{Javadoc:SE|package=java.net|java/net|ServerSocket}}, or {{Javadoc:SE|package=java.net|java/net|Socket}}, and vice versa. Channels are analogous to "[[file descriptor]]s" found in Unix-like operating systems.

[[Computer file|File]] channels ({{Javadoc:SE|package=java.nio.channels|java/nio/channels|FileChannel}}) can use arbitrary buffers but can also establish a buffer directly mapped to file contents using [[memory-mapped file]].  They  can also interact with [[file system]] locks. Similarly, [[Internet socket|socket]] channels ({{Javadoc:SE|package=java.nio.channels|java/nio/channels|SocketChannel}} and {{Javadoc:SE|package=java.nio.channels|java/nio/channels|ServerSocketChannel}}) allow for data transfer between sockets and NIO buffers.

<code>FileChannel</code> can be used to do a file copy, which is potentially far more efficient than using old read/write with a byte array. The typical code for this is:
<syntaxhighlight lang="java">
// Getting file channels
try(FileChannel in = FileChannel.open(source, StandardOpenOption.READ);
    FileChannel out = FileChannel.open(target, StandardOpenOption.WRITE)) {

    // JavaVM does its best to do this as native I/O operations.
    in.transferTo(0, in.size(), out);
}

</syntaxhighlight>