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Java NIO Channel


Java Nio 

1Java NIO Tutorial
2Java NIO Overview
3Java NIO Channel
4Java NIO Buffer
5Java NIO Scatter / Gather
6Java NIO Channel to Channel Transfers
7Java NIO Selector
8Java NIO FileChannel
9Java NIO SocketChannel
10Java NIO ServerSocketChannel
11Java NIO DatagramChannel
12Java NIO Pipe
13Java NIO vs. IO

Java NIO Channel

 
By Jakob Jenkov
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Java NIO Channels are similar to 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.
  • Channels always read to, or write from, a Buffer.

As mentioned above, you read data from a channel into a buffer, and write data from a buffer into a channel. Here is an illustration of that:

Java NIO: Channels and Buffers
Java NIO: Channels read data into Buffers, and Buffers write data into Channels

Channel Implementations

Here are the most important Channel implementations in Java NIO:

  • FileChannel
  • DatagramChannel
  • SocketChannel
  • ServerSocketChannel

The FileChannel reads data from and to files.

The DatagramChannel can read and write data over the network via UDP.

The SocketChannel can read and write data over the network via TCP.

The ServerSocketChannel allows you to listen for incoming TCP connections, like a web server does. For each incoming connection a SocketChannel is created.

Basic Channel Example

Here is a basic example that uses a FileChannel to read some data into a Buffer:

    RandomAccessFile aFile = new RandomAccessFile("data/nio-data.txt", "rw");
    FileChannel inChannel = aFile.getChannel();

    ByteBuffer buf = ByteBuffer.allocate(48);

    int bytesRead = inChannel.read(buf);
    while (bytesRead != -1) {

      System.out.println("Read " + bytesRead);
      buf.flip();

      while(buf.hasRemaining()){
          System.out.print((char) buf.get());
      }

      buf.clear();
      bytesRead = inChannel.read(buf);
    }
    aFile.close();

Notice the buf.flip() call. First you read into a Buffer. Then you flip it. Then you read out of it. I‘ll get into more detail about that in the next text about Buffer‘s.







Java NIO Channel