从输入流读取字节

public static byte[] readBytes(InputStream in) throws IOException {  
    //读取字节的缓冲
    byte[] buffer = new byte[1024];
    //最终的数据
    byte[] result = new byte[0];
    int size = 0;  
    while ((size = in.read(buffer)) != -1) {  
        int oldLen = result.length;
        byte[] tmp = new byte[oldLen + size];
        if (oldLen > 0) {//copy 旧字节
            System.arraycopy(result, 0, tmp, 0, oldLen);
        }
        //copy 新字节
        System.arraycopy(buffer, 0, tmp, oldLen, size);
        
        result = tmp;
    }  
    return result;
}