Java NIO基础知识

java NIO比普通IO访问速度有较大的提高，原因是新IO所使用的结构接近于操作系统执行IO的方式：通道和缓冲器。唯一直接与通道交互的缓冲期是ByteBuffer.
参考下面的例子:

public class GetChannel {

	private static final int BSIZE=1024;
	public static void main(String[] args) throws Exception{
		FileChannel fc=new FileOutputStream("D:\\data.txt").getChannel();
		fc.write(ByteBuffer.wrap("Some text".getBytes()));
		fc.close();

		fc=new RandomAccessFile("D:\\data.txt","rw").getChannel();
		fc.position(fc.size());
		fc.write(ByteBuffer.wrap("Some more".getBytes()));
		fc.close();

		fc=new FileInputStream("D:\\data.txt").getChannel();
		ByteBuffer buff=ByteBuffer.allocate(BSIZE);
		fc.read(buff);

		//一旦调用read()来告知FileChannel向ByteBuffer存储字节，就
		//必须调用缓冲期上的flip(),让它做好让别人读取字节的准备

		buff.flip();
		while(buff.hasRemaining())
			System.out.print((char)buff.get());

	}
}

如果我们进一步read(),则先清空ByteBuffer,参见如下代码:

FileChannel in =new FileInputStream("aa.txt").getChannel(),
FileChannel out =new FileInputStream("aa.txt").getChannel(),
ByteBuffer buffer=ByteBuffer.allocate(1024);
while(in.read(buffer)!=-1)
{
    buffer.flip();
    out.write(buffer);
    //
    buffer.clear();
}