导入Excel和CSV文件

　　读取excel或csv文件中的数据暂时保存在DataTable中， 代码如下：

    public static DataTable ReadDataFromFile(string file, string sheet)
    {
        string strConn = "";
        string extension = Path.GetExtension(file);
        string sqlStr = string.Empty;
        if (extension == ".csv")
        {
            strConn = string.Format("Provider=Microsoft.Jet.OLEDB.4.0;Extended Properties='text;HDR=Yes;FMT=Delimited';Data Source={0}", Path.GetDirectoryName(file));
            sqlStr = string.Format("select * from {0}", Path.GetFileName(file));
        }
        else if (extension == ".xls")
        {
            strConn = string.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties='Excel 8.0;HDR=YES;'", file);
            sqlStr = string.Format("SELECT * FROM [{0}$]", sheet);
        }
        else if (extension == ".xlsx")
        {
            strConn = string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=Excel 12.0;", file);
            sqlStr = string.Format("SELECT * FROM [{0}$]", sheet);
        }
        else
        {
            throw new Exception(string.Format("不支持的导入扩展名为{0}的文件！", extension));
        }

        OleDbConnection conn = new OleDbConnection(strConn);
        OleDbDataAdapter myCommand = new OleDbDataAdapter(sqlStr, strConn);
        DataTable dt = new DataTable();
        try
        {
            myCommand.Fill(dt);
        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            conn.Close();
        }
        return dt;
    }