关于request.getinputStream读取一次的问题研究

    public int substract( byte src[], int off, int len )
        throws IOException {

        if ((end - start) == 0) {
            if (in == null)
                return -1;
//重点，进行流读取标识，读到末尾，会返回-1，里边realReadBytes的方法进行了详细的处理
 int n = in.realReadBytes( buff, 0, buff.length );
            if (n < 0)
                return -1;
        }

        int n = len;
        if (len > getLength()) {
            n = getLength();
        }
//进行流的复制，从socket到应用层
 System.arraycopy(buff, start, src, off, n);
        start += n;
        return n;

    }