code: public static int copy(InputStream in, OutputStream out) throws IOException {
          BeanUtil.requireNonNull(in, "No InputStream specified");
          BeanUtil.requireNonNull(out, "No OutputStream specified");
          int byteCount = 0;
          byte[] buffer = new byte[4096];
          int bytesRead1;
          for (; (bytesRead1 = in.read(buffer)) != -1; byteCount += bytesRead1) {
              out.write(buffer, 0, bytesRead1);
          }
          out.flush();
          return byteCount;
      }
docs: 将输入流的内容复制到输出流里
  
  @param in  输入流
  @param out 输出流
  @return 复制的数据字节数
  @throws IOException IO异常