import java.io.*;
class bufferInputStream {

    public static void main(String[] args) throws IOException
    {
        try {
            File file=new File("f:/work/file2.txt");
            long len=file.length();
            System.out.println("changdu" + len);
            byte[] bytes = new byte[(int)len];
            
            FileInputStream f=new FileInputStream(file);
            BufferedInputStream bs=new BufferedInputStream(f);
            while(bs.read()!=-1)
            {
                bs.read(bytes,0,((int)len));
                System.out.println(new String(bytes));
            }
            bs.close();
        } catch (Exception e) {
            e.printStackTrace();
        }    
    }
}

File file=new File("f:/work/file2.txt");
byte[] buf = new byte[1024];
int size = 0;

StringBuilder sb = new StringBuilder();

InputStream is = new FileInputStream(file);
while((size = is.read(buf)) != -1)
  sb.append(new String(buf,0,size));

is.close();
System.out.println(sb.toString());

------解决方案--------------------

Java code

class BufferInputStream {

    public static void main(String[] args) throws IOException {
        try {
            File file = new File("F:/work/file2.txt");
            long len = file.length();
            System.out.println("changdu:" + len);
            byte[] bytes = new byte[(int) len];

            FileInputStream f = new FileInputStream(file);
            BufferedInputStream bs = new BufferedInputStream(f);
            while (true) { //楼主的代码此处就读了一次数据
                int key = bs.read(bytes, 0, ((int) len));
                System.out.println(new String(bytes));
                if (key == -1)
                    break;
            }
            bs.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

------解决方案--------------------
把循环去掉就可以了 
因为你在判断while的条件的时候，读了第一个字符，这时候流里边第一个字符已经没了，只剩下“234567”六个字符，所以你读7个的时候，只能读出“234567”，外加一个数组结束符\0，

你把代码改成这样就可以  读出7个数字了：
                       byte[] bytes = new byte[(int) len];

			FileInputStream f = new FileInputStream(file);
			BufferedInputStream bs = new BufferedInputStream(f);

			bs.read(bytes, 0, ((int) len));

			System.out.println(new String(bytes));