File Upload/download is a technology that we often use in the actual project development process. Several common methods are provided here. The main content of this article includes:
1. How to Solve the file upload size limit
2. Save the file to the server
3. convert to a binary byte stream, save it to the database, and download it
4. Upload Internet Resources
Part 1:
First, let's talk about how to solve the file upload size limit in Asp.net. We know ASP by default.. Net file upload size is limited to 2 MB. In general, we can change the web. the config file defines the maximum file size as follows:
<Httpruntime executiontimeout = "300" maxrequestlength = "40960" usefullyqualifiedredirecturl = "false"/> in this way, the maximum value of the uploaded file is 4 MB, however, this does not allow us to infinitely expand the value of maxrequestlength, because ASP. net loads all files into the memory and then processes them. The solution is to use the implicit httpworkerrequest and its getpreloadedentitybody and readentitybody methods to read data from the pipe created by IIS for ASP. NET in blocks. The implementation method is as follows:
Iserviceproviderprovider = (iserviceprovider) httpcontext. Current;
Httpworkerrequestwr = (httpworkerrequest) provider. getservice (typeof (httpworkerrequest ));
Byte [] BS = Wr. getpreloadedentitybody ();
.
If (! Wr. isentireentitybodyispreloaded ())
{
INTN = 1024;
Byte [] bs2 = newbyte [N];
While (WR. readentitybody (bs2, n)> 0)
{
..
}
}
This solves the problem of uploading large files.
Part 2:
Next we will introduce how to upload a client file to the server as a file and return some basic information about the uploaded file.
First, we define a class to store the information of the uploaded file (required when returned ).
Public class fileupload
{
Public fileupload ()
{}
/** // <Summary>
/// Upload File Name
/// </Summary>
Public String filename
{
Get
{
Return filename;
}
Set
{
Filename = value;
}
}
Private string filename;
/** // <Summary>
/// Upload File Path
/// </Summary>
Public String filepath
{
Get
{
Return filepath;
}
Set
{
Filepath = value;
}
}
Private string filepath;
/** // <Summary>
/// File Extension
/// </Summary>
Public String fileextension
{
Get
{
Return fileextension;
}
Set
{
Fileextension = value;
}
}
Private string fileextension;
}
In addition, you can restrict the format of the uploaded file (App. config) in the configuration file ):
<? XML version = "1.0" encoding = "gb2312"?>
<Application>
<Fileupload>
<Format>. jpg |. gif |. PNG |. BMP </format>
</Fileupload>
</Application>
In this way, we can start writing our file upload method as follows:
Public fileupload uploadfile (htmlinputfile inputfile, string filepath, string myfilename, bool israndom)
{
Fileupload fp = new fileupload ();
String filename, fileextension;
String savename;
//
// Create an upload object
//
Httppostedfile postedfile = inputfile. postedfile;
Filename = system. Io. Path. getfilename (postedfile. filename );
Fileextension = system. Io. Path. getextension (filename );
//
// Determine the file format based on the Type
//
Appconfig APP = new appconfig ();
String format = app. getpath ("fileupload/format ");
//
// Return if none of the formats are correct
//
If (format. indexof (fileextension) =-1)
{
Throw new applicationexception ("the format of uploaded data is invalid ");
}
//
// Generate a random file name based on the date and random number.
//
If (myfilename! = String. Empty)
{
Filename = myfilename;
}
If (israndom)
{
Random objrand = new random ();
System. datetime date = datetime. now;
// Generate random file names
Savename = date. year. tostring () + date. month. tostring () + date. day. tostring () + date. hour. tostring () + date. minute. tostring () + date. second. tostring () + convert. tostring (objrand. next (99) * 97 + 100 );
Filename = savename + fileextension;
}
String phypath = httpcontext. Current. Request. mappath (filepath );
// Determine whether a path exists. If not, create a path.
Directoryinfo updir = new directoryinfo (phypath );
If (! Updir. exists)
{
Updir. Create ();
}
//
// Save the file
//
Try
{
Postedfile. saveas (phypath + filename );
FP. filepath = filepath + filename;
FP. fileextension = fileextension;
FP. filename = filename;
}
Catch
{
Throw new applicationexception ("Upload Failed! ");
}
// Return the information of the uploaded object
Return FP;
}
Then we can call this method when uploading files, and save the returned file information to the database. As for downloading, it is OK to open the path directly.
