让PdfStamper使用MemoryStreams(c#,itextsharp)

Question

我找到了重新编写旧代码的方法,这些代码将PDF文件签名为新文件,这标志着来自Web服务的MemoryStreams(字节数组).简单吧？那是昨天.今天我无法让它发挥作用.

这是旧代码,它使用FileStreams并且它可以工作:

    public static string OldPdfSigner(PdfReader pdfReader, string destination, string password, string reason, string location, string pathToPfx)
    {
        using (FileStream pfxFile = new FileStream(pathToPfx, FileMode.Open, FileAccess.Read))
        {
            ...

            using (PdfStamper st = PdfStamper.CreateSignature(pdfReader, new FileStream(destination, FileMode.Create, FileAccess.Write), '\0'))
            {
                PdfSignatureAppearance sap = st.SignatureAppearance;
                sap.SetCrypto(key, chain, null, PdfSignatureAppearance.WINCER_SIGNED);
                sap.Reason = reason;
                sap.Location = location;
                return destination;
            }
        }
    }

下面是我自己重做的内容,它抛出System.ObjectDisposedException:无法访问已关闭的Stream.

    public static byte[] PdfSigner(PdfReader pdfReader, string password, string reason, string location, string pathToPfx)
    {
        using (FileStream pfxFile = new FileStream(pathToPfx, FileMode.Open, FileAccess.Read))
        {
            ...

            MemoryStream outputStream = new MemoryStream();
            using (PdfStamper st = PdfStamper.CreateSignature(pdfReader, outputStream, '\0'))
            {
                st.Writer.CloseStream = false;
                PdfSignatureAppearance sap = st.SignatureAppearance;
                sap.SetCrypto(key, chain, null, PdfSignatureAppearance.WINCER_SIGNED);
                sap.Reason = reason;
                sap.Location = location;
                st.Close();
                outputStream.Position = 0;
                return outputStream.ToArray();
            }
        }
    }

如果我发表评论

st.Close();

它会创建一个空文档.我究竟做错了什么？

Answer 1

不是特定于您的签名代码,但在使用MemoryStream和时PdfStamper,请遵循以下常规模式:

using (MemoryStream ms = new MemoryStream()) {
  using (PdfStamper stamper = new PdfStamper(reader, ms, '\0', true)) {
// do stuff      
  }    
  return ms.ToArray();
}

• MemoryStream实现IDisposable,所以包括一个using声明.
• 该PdfStamper using语句负责处理对象,因此您不需要调用Close(),也不需要设置CloseStream属性.
• 您的代码片段在语句中过早地返回字节数组PdfStamper using,因此您MemoryStream实际上是无操作.返回的字节数组之外的的PdfStamper using声明,以及内部的MemoryStream using声明.
• 通常不需要重置MemoryStream Position属性.
• 忽略PdfStamper上面的构造函数 - 它来自我填写表单的一些测试代码,并使用你需要的任何构造函数/方法进行签名.