第三节 netty前传-NIO中缓冲buffer-01

public abstract class Buffer {
    // Cached unsafe-access object
    static final Unsafe UNSAFE = Unsafe.getUnsafe();
    /**
     * The characteristics of Spliterators that traverse and split elements
     * maintained in Buffers.
     */
    static final int SPLITERATOR_CHARACTERISTICS =
        Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.ORDERED;

    // Invariants: mark <= position <= limit <= capacity
    private int mark = -1;
    private int position = 0;
    private int limit;
    private int capacity;
//略。。。
}

public class ReadFile {
    public static void main(String[] args){
        readFile();
    }
    public static void readFile(){
        try(RandomAccessFile randomAccessFile =
                    new RandomAccessFile("F:\\data\\test.txt","rw")){
            //获取连接通道
            FileChannel fileChannel = randomAccessFile.getChannel();
            //初始化一个缓冲区，大小为1024byte
            ByteBuffer buf = ByteBuffer.allocate(1024);
            //fileChannel.read(buf)从通道中读取文件的数据放入缓冲区，返回结构为读取的字节数
            //注意：这个方法会记录读取的位置，所以后续读取不会从头开始读取
            int bytesRead = fileChannel.read(buf);
            System.out.println(bytesRead);
            //读取到数据
            while(bytesRead != -1)
            {
                //反转后为可以读取缓冲中的数据
                buf.flip();
                while(buf.hasRemaining())//position < limit;表示可读
                {
                    //读取
                    System.out.print((char)buf.get());
                }
                //没有可读数据后，清除已读数据，从未读数据之后开始写入
                buf.compact();
                //开始继续读取
                bytesRead = fileChannel.read(buf);
            }
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}