Question

已经从UI中将.xlsx文件保存到数据库中。现在我正在使用下面的代码从数据库中读取数据并将其写入临时位置文件。

    Dim Buffer() As Byte
    Dim Amount As Integer = 2000
    Dim TripCount As Integer = 0
    Dim reminder As Integer = 0

           ReDim Buffer(FileSize)
            TripCount = FileSize \ Amount
            reminder = FileSize Mod Amount

           If reminder > 0 Then
                TripCount = TripCount + 1
            End If
          For cnt As Integer = 0 To TripCount - 1

                Dim Offset As Integer = 1
                Offset = Offset + cnt * Amount

                Dim ReadCount As Integer = Amount
                If cnt = TripCount - 1 Then
                    ReadCount = CInt(FileSize) - (cnt * Amount)
                End If

                Dim b() As Byte = GetFileData(CLng(documentId), ReadCount, Offset) 'GetFileData methdo as last code segment

                Array.Copy(b, 0, Buffer, Offset - 1, b.Length)


            Next            

            Dim downloadFile As New FileInfo(selectedPath + "\" + FileName)

            Using bw As New BinaryWriter(downloadFile.OpenWrite)
                bw.Write(Buffer)
                bw.Close()
            End Using

Public Function GetFileData(ByVal documentId As Long, ByVal amount As Integer, ByVal offset As Integer) As Byte()
    Dim RetVal() As Byte = Nothing
    Dim b1 As Byte() = Nothing
    Try
        Dim sql As String = ""
        ReDim RetVal(amount)
        sql = "  SELECT  DBMS_LOB.SUBSTR(F.DF_FILE," + amount.ToString + "," + offset.ToString + "   ) DATA"
        sql += " FROM table_name F"
        sql += " WHERE F.docid = " + documentId.ToString

        Dim data As DataTable = FetchData(sql)

        b1 = CType(data.Rows(0)("DATA"), Byte())
        Array.Copy(b1, 0, RetVal, 0, b1.Length)
    Catch ex As Exception

    End Try

    Return RetVal
End Function

将文件放入临时位置后，我试图打开它，但它会丢失以下错误。

Excel在＆＃39; filename.xlsx＆＃39;中找到了不可读的内容。你想恢复这个工作簿的内容吗？如果您信任此工作簿的来源，请单击是

但是同一组代码适用于.xls格式文件。

Answer 1

问题在于数组大小。

如果文件大小为2000字节。那么

        Redim Buffer(FileSize)

此缓冲区的Redim数组大小将为2000 + 1 = 2001

然后从数据库获取并放入Buffer数组并将其写入文件，如下所示。

        Dim downloadFile As New FileInfo(selectedPath + "\" + FileName)
        Using bw As New BinaryWriter(downloadFile.OpenWrite)
            bw.Write(Buffer)
            bw.Close()
        End Using

文件大小增加1个字节。在这种情况下，文件大小为2001字节。所以它显示错误。

现在我已经用下面的内容替换了上面的内容，并且它完美无缺。

         Using bw As New BinaryWriter(downloadFile.OpenWrite)   
             Dim newBuffer(((Buffer.Length) - 2)) As Byte
             Array.Copy(Buffer, 0, newBuffer, 0, ((Buffer.Length) - 2))
             bw.Write(newBuffer)
             bw.Close()
         End Using

在上面的代码中我已经声明了另一个新数组newBuffer并将数据从旧数组Buffer复制到新数组newBuffer，从0索引到（旧数组的长度 - 2）以容纳文件大小。

.xlsx文件的读/写操作

1 个答案: