c# - 将 pdf 转换为来自 url 的流

Question

我有一个 PDF 托管在 http://test.com/mypdf.pdf 中.

如何将 PDF 转换为 Stream，然后使用此 Stream 将其转换回 PDF。

我尝试了以下但出现异常(见图):

private static Stream ConvertToStream(string fileUrl)
{
    HttpWebResponse aResponse = null;
    try
    {
        HttpWebRequest aRequest = (HttpWebRequest)WebRequest.Create(fileUrl);
        aResponse = (HttpWebResponse)aRequest.GetResponse();
    }
    catch (Exception ex)
    {

    }

    return aResponse.GetResponseStream();
}

Answer 1

这将起作用:

private static Stream ConvertToStream(string fileUrl)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(fileUrl);
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();

    try {
        MemoryStream mem = new MemoryStream();
        Stream stream = response.GetResponseStream();

        stream.CopyTo(mem,4096);

        return mem;
    } finally {
        response.Close();
    }
}

但是，您对返回的内存流的生命周期负全部责任。

更好的方法是:

private static void ConvertToStream(string fileUrl, Stream stream)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(fileUrl);
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();

    try {
        Stream response_stream = response.GetResponseStream();

        response_stream.CopyTo(stream,4096);
    } finally {
        response.Close();
    }
}

然后您可以执行以下操作:

using (MemoryStream mem = new MemoryStream()) {
    ConvertToStream('http://www.example.com/',mem);
    mem.Seek(0,SeekOrigin.Begin);

    ... Do something else ...
}

您也可以直接返回响应流，但您必须检查它的生命周期，释放响应可能释放流，从而释放内存副本。