Java RandomAccessFile基本文件操作示例

package com.imooc.io;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;
public class RafDemo {
    /**
     * @param args
     */
    public static void main(String[] args) throws IOException{
        File demo = new File("demo");
        if(!demo.exists())
            demo.mkdir();
        File file = new File(demo,"raf.dat");
        if(!file.exists())
            file.createNewFile();
        RandomAccessFile raf = new RandomAccessFile(file, "rw");
        //指针的位置
        System.out.println(raf.getFilePointer());
        raf.write('A');//只写了一个字节
        System.out.println(raf.getFilePointer());
        raf.write('B');
        int i = 0x7fffffff;
        //用write方法每次只能写一个字节，如果要把i写进去就得写4次
        raf.write(i >>> 24);//高8位
        raf.write(i >>> 16);
        raf.write(i >>> 8);
        raf.write(i);
        System.out.println(raf.getFilePointer());
        //可以直接写一个int
        raf.writeInt(i);
        String s = "中";
        byte[] gbk = s.getBytes("gbk");
        raf.write(gbk);
        System.out.println(raf.length());
        //读文件，必须把指针移到头部
        raf.seek(0);
        //一次性读取,把文件中的内容都读到字节数组中
        byte[] buf = new byte[(int)raf.length()];
        raf.read(buf);
        System.out.println(Arrays.toString(buf));
      for (byte b : buf) {
            System.out.println(Integer.toHexString(b & 0xff)+" ");
        }
      raf.close();
    }
}