将 blob 转换回原始文件类型并使其可供下载

Question

所以我有一个使用 HTML5 和 JavaScript 构建的客户端应用程序。我的应用程序调用 Web 服务（使用 c# 构建），该服务从 MySql 数据库中提取 blob 数据并将其传递给客户端应用程序。

这个 blob 数据实际上是一个存储在 MySQL 数据库中的小文件（小于 100kb）。我希望我的客户端应用程序能够将此 blob 转换回其原始文件类型，然后向用户询问下载权限。现在我想知道这是否是个好主意？还是我应该简单地在我的 Web 服务中进行文件转换，然后将文件本身发送到 JSP 应用程序？

任何帮助/建议将不胜感激！如果您有任何好的教程/代码，这可能会帮助我进行转换，那么请将它们发布在这里作为答案？提前致谢！

Answer 1

使用此示例并将 SQL 数据库更改为您的数据库以及 Select 语句

SqlConnection pubsConn = new SqlConnection("Data Source=localhost;Integrated Security=SSPI;Initial Catalog=pubs;");
SqlCommand logoCMD = new SqlCommand("SELECT pub_id, logo FROM pub_info", pubsConn);

FileStream fs;                          // Writes the BLOB to a file (*.bmp).
BinaryWriter bw;                        // Streams the BLOB to the FileStream object.

int bufferSize = 100;                   // Size of the BLOB buffer.
byte[] outbyte = new byte[bufferSize];  // The BLOB byte[] buffer to be filled by GetBytes.
long retval;                            // The bytes returned from GetBytes.
long startIndex = 0;                    // The starting position in the BLOB output.

string pub_id = "";                     // The publisher id to use in the file name.

// Open the connection and read data into the DataReader.
pubsConn.Open();
SqlDataReader myReader = logoCMD.ExecuteReader(CommandBehavior.SequentialAccess);

while (myReader.Read())
{
  // Get the publisher id, which must occur before getting the logo.
  pub_id = myReader.GetString(0);  

  // Create a file to hold the output.
  fs = new FileStream("logo" + pub_id + ".bmp", FileMode.OpenOrCreate, FileAccess.Write);
  bw = new BinaryWriter(fs);

  // Reset the starting byte for the new BLOB.
  startIndex = 0;

  // Read the bytes into outbyte[] and retain the number of bytes returned.
  retval = myReader.GetBytes(1, startIndex, outbyte, 0, bufferSize);

  // Continue reading and writing while there are bytes beyond the size of the buffer.
  while (retval == bufferSize)
  {
    bw.Write(outbyte);
    bw.Flush();

    // Reposition the start index to the end of the last buffer and fill the buffer.
    startIndex += bufferSize;
    retval = myReader.GetBytes(1, startIndex, outbyte, 0, bufferSize);
  }

  // Write the remaining buffer.
  bw.Write(outbyte, 0, (int)retval - 1);
  bw.Flush();

  // Close the output file.
  bw.Close();
  fs.Close();
}

// Close the reader and the connection.
myReader.Close();
pubsConn.Close();