F ileUpload Ser ver Control In ASP.NET 1.0/1.1, you could upload files using the HTML FileUpload server control.. ASP.NET 2.0 introduced a new FileUpload server control that makes the pr
Trang 1protected void HiddenField1_ValueChanged(object sender, EventArgs e)
{
// Handle event here
}
TheValueChangedevent is triggered when the ASP.NET page is posted back to the server if the value
of the HiddenField server control has changed since the last time the page was drawn If the value has
not changed, the method is never triggered Therefore, the method is useful to act upon any changes to
the HiddenField control — such as recording a value to the database or changing a value in the user’s
profile
F ileUpload Ser ver Control
In ASP.NET 1.0/1.1, you could upload files using the HTML FileUpload server control This control put
an<input type="file">element on your Web page to enable the end user to upload files to the server
To use the file, however, you had to make a couple of modifications to the page For example, you were
required to addenctype="multipart/form-data"to the page’s<form>element
ASP.NET 2.0 introduced a new FileUpload server control that makes the process of uploading files to
a server even simpler When giving a page the capability to upload files, you simply include the new
<asp:FileUpload>control and ASP.NET takes care of the rest, including adding theenctypeattribute
to the page’s<form>element
Uploading Files Using the FileUpload Control
After the file is uploaded to the server, you can also take hold of the uploaded file’s properties and either
display them to the end user or use these values yourself in your page’s code behind Listing 3-34 shows
an example of using the new FileUpload control The page contains a single FileUpload control, plus a
Button and a Label control
Listing 3-34: Uploading files using the new FileUpload control
VB
<%@ Page Language="VB"%>
<script runat="server">
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
If FileUpload1.HasFile Then Try
FileUpload1.SaveAs("C:\Uploads\" & _ FileUpload1.FileName)
Label1.Text = "File name: " & _ FileUpload1.PostedFile.FileName & "<br>" & _
"File Size: " & _ FileUpload1.PostedFile.ContentLength & " kb<br>" & _
"Content type: " & _ FileUpload1.PostedFile.ContentType
Trang 2Catch ex As Exception Label1.Text = "ERROR: " & ex.Message.ToString() End Try
Else
Label1.Text = "You have not specified a file."
End If
End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>FileUpload Server Control</title>
</head>
<body>
<form id="form1" runat="server">
<asp:FileUpload ID="FileUpload1" runat="server" />
<p>
<asp:Button ID="Button1" runat="server" Text="Upload"
OnClick="Button1_Click" /></p>
<p>
<asp:Label ID="Label1" runat="server"></asp:Label></p>
</form>
</body>
</html>
C#
<%@ Page Language="C#"%>
<script runat="server">
protected void Button1_Click(object sender, EventArgs e)
{
if (FileUpload1.HasFile)
try {
FileUpload1.SaveAs("C:\\Uploads\\" + FileUpload1.FileName);
Label1.Text = "File name: " + FileUpload1.PostedFile.FileName + "<br>" +
FileUpload1.PostedFile.ContentLength + " kb<br>" +
"Content type: " + FileUpload1.PostedFile.ContentType;
}
catch (Exception ex) { Label1.Text = "ERROR: " + ex.Message.ToString();
} else
{
Label1.Text = "You have not specified a file.";
}
}
</script>
From this example, you can see that the entire process is rather simple The single button on the page
initiates the upload process The FileUpload control itself does not initiate the uploading process You
must initiate it through another event such asButton_Click
Trang 3When compiling and running this page, you may notice a few things in the generated source code of the
page An example of the generated source code is presented here:
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1"><title>
FileUpload Server Control
</title></head>
<body>
<form name="form1" method="post" action="FileUpload.aspx" id="form1"
enctype="multipart/form-data">
<div>
<input type="hidden" name=" VIEWSTATE" id=" VIEWSTATE"
value="/wEPDwUKMTI3ODM5MzQ0Mg9kFgICAw8WAh4HZW5jdHlwZQUTbXVsdGlwYXJ0L2Zvcm
0tZGF0YWRkrSpgAFaEKed5+5/8+zKglFfVLCE=" />
</div>
<input type="file" name="FileUpload1" id="FileUpload1" />
<p>
<input type="submit" name="Button1" value="Upload" id="Button1" /></p>
<p>
<span id="Label1"></span></p>
<div>
<input type="hidden" name=" EVENTVALIDATION" id=" EVENTVALIDATION"
value="/wEWAgL1wLWICAKM54rGBqfR8MhZIDWVowox+TUvybG5Xj0y" />
</div></form>
</body>
</html>
The first thing to notice is that because the FileUpload control is on the page, ASP.NET 3.5 modified the
page’s<form>element on your behalf by adding the appropriateenctypeattribute Also notice that the
FileUpload control was converted to an HTML<input type="file">element
After the file is uploaded, the first check (done in the file’sButton1_Clickevent handler) examines
whether a file reference was actually placed within the<input type="file">element If a file was
specified, an attempt is made to upload the referenced file to the server using theSaveAs()method of
the FileUpload control That method takes a singleStringparameter, which should include the location
where you want to save the file In theStringparameter used in Listing 3-34, you can see that the file is
being saved to a folder calledUploads, which is located in theC:\drive
ThePostedFile.FileNameattribute is used to give the saved file the same name as the file it was copied
from If you want to name the file something else, simply use theSaveAs()method in the following
manner:
FileUpload1.SaveAs("C:\Uploads\UploadedFile.txt")
You could also give the file a name that specifies the time it was uploaded:
FileUpload1.SaveAs("C:\Uploads\" & System.DateTime.Now.ToFileTimeUtc() & ".txt")
After the upload is successfully completed, the Label control on the page is populated with metadata of
the uploaded file In the example, the file’s name, size, and content type are retrieved and displayed on
Trang 4the page for the end user When the file is uploaded to the server, the page generated is similar to that
shown in Figure 3-37
Figure 3-37
Uploading files to another server can be an error-prone affair It is vital to upload files in your code using proper exception handling That is why the file in the example is uploaded using aTry Catchstatement
Giving ASP.NET Proper Permissions to Upload Files
You might receive errors when your end users upload files to your Web server through the FileUpload control in your application These might occur because the destination folder on the server is not writable for the account used by ASP.NET If ASP.NET is not enabled to write to the folder you want, you can
enable it using the folder’s properties
First, right-click on the folder where the ASP.NET files should be uploaded and select Properties from the provided menu The Properties dialog for the selected folder opens Click the Security tab to make sure the ASP.NET Machine Account is included in the list and has the proper permissions to write to disk If
it is enabled, you see something similar to what is presented in Figure 3-38
If you do not see the ASP.NET Machine Account in the list of users allowed to access the folder, add
ASP.NET by clicking the Add button and entering ASPNET (without the period) in the text area provided (see Figure 3-39)
Click OK, and you can then click the appropriate check boxes to provide the permissions needed for your application
Understanding File Size Limitations
Your end users might never encounter an issue with the file upload process in your application, but you should be aware that some limitations exist When users work through the process of uploading files, a size restriction is actually sent to the server for uploading The default size limitation is 4 MB (4096 KB); the transfer fails if a user tries to upload a file that is larger than 4096 KB
Trang 5Figure 3-38
Figure 3-39
A size restriction protects your application You want to prevent malicious users from uploading
numer-ous large files to your Web server in an attempt to tie up all the available processes on the server Such an
occurrence is called a denial of service attack It ties up the Web server’s resources so that legitimate users
are denied responses from the server
Trang 6One of the great things about NET, however, is that it usually provides a way around limitations You can usually change the default settings that are in place To change the limit on the allowable upload
file size, you make some changes in either the rootweb.configfile (found in the ASP.NET 2.0
config-uration folder atC:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\CONFIG) or in your application’s
web.configfile
In theweb.configfile, you can create a node called<httpRuntime> In this file, you apply the settings
so that the default allowable file size is dictated by the actual request size permitted to the Web server
(4096 KB) The<httpRuntime>section of theweb.config.commentsfile is shown in Listing 3-35
Listing 3-35: Changing the file-size limitation setting in the web.config file
<httpRuntime
executionTimeout="110"
maxRequestLength="4096"
requestLengthDiskThreshold="80"
useFullyQualifiedRedirectUrl="false"
minFreeThreads="8"
minLocalRequestFreeThreads="4"
appRequestQueueLimit="5000"
enableKernelOutputCache="true"
enableVersionHeader="true"
requireRootedSaveAsPath="true"
enable="true"
shutdownTimeout="90"
delayNotificationTimeout="5"
waitChangeNotification="0"
maxWaitChangeNotification="0"
enableHeaderChecking="true"
sendCacheControlHeader="true"
apartmentThreading="false" />
You can do a lot with the<httpRuntime>section of theweb.configfile, but two properties — the maxRe-questLengthandexecutionTimeoutproperties — are especially interesting
ThemaxRequestLengthproperty is the setting that dictates the size of the request made to the Web server When you upload files, the file is included in the request; you alter the size allowed to be uploaded by
changing the value of this property The value presented is in kilobytes To allow files larger than the
default of 4 MB, change themaxRequestLengthproperty as follows:
maxRequestLength="11000"
This example changes themaxRequestLengthproperty’s value to 11,000 KB (around 10 MB) With this set-ting in place, your end users can upload 10 MB files to the server When changing themaxRequestLength
property, be aware of the setting provided for theexecutionTimeoutproperty This property sets the
time (in seconds) for a request to attempt to execute to the server before ASP.NET shuts down the
request (whether or not it is finished) The default setting is90seconds The end user receives a
time-out error notification in the browser if the time limit is exceeded If you are going to permit larger
requests, remember that they take longer to execute than smaller ones If you increase the size of the
maxRequestLengthproperty, you should examine whether to increase theexecutionTimeoutproperty
as well
Trang 7If you are working with smaller files, it is advisable to reduce the size allotted for the request to the Web
server by decreasing the value of themaxRequestLengthproperty This helps safeguard your application
from a denial of service attack.
Making these changes in theweb.configfile applies this setting to all the applications that are on the
server If you want to apply this only to the application you are working with, apply the<httpRuntime>
node to theweb.configfile of your application, overriding any setting that is in the rootweb.configfile
Make sure this node resides between the<system.web>nodes in the configuration file
Uploading Multiple Files from the Same Page
So far, you have seen some good examples of how to upload a file to the server without much hassle
Now, look at how to upload multiple files to the server from a single page
No built-in capabilities in the Microsoft NET Framework enable you to upload multiple files from a
single ASP.NET page With a little work, however, you can easily accomplish this task just as you would
have in the past using NET 1.x.
The trick is to import theSystem.IOclass into your ASP.NET page and then to use the
HttpFileCollec-tionclass to capture all the files that are sent in with theRequestobject This approach enables you to
upload as many files as you want from a single page
If you wanted to, you could simply handle each and every FileUpload control on the page individually,
as shown in Listing 3-36
Listing 3-36: Handling each FileUpload control individually
VB
If FileUpload1.HasFile Then
’ Handle file
End If
If FileUpload2.HasFile Then
’ Handle file
End If
C#
if (FileUpload1.HasFile) {
// Handle file
}
if (FileUpload2.HasFile) {
// Handle file
}
If you are working with a limited number of file upload boxes, this approach works; but at the same
time you may, in certain cases, want to handle the files using theHttpFileCollectionclass This is
especially true if you are working with a dynamically generated list of server controls on your ASP
.NET page
Trang 8For an example of this, you can build an ASP.NET page that has three FileUpload controls and one
Submit button (using the Button control) After the user clicks the Submit button and the files are posted
to the server, the code behind takes the files and saves them to a specific location on the server After the files are saved, the file information that was posted is displayed in the ASP.NET page (see Listing 3-37)
Listing 3-37: Uploading multiple files to the server
VB
Protected Sub Button1_Click(ByVal sender As Object, _
ByVal e As System.EventArgs)
Dim filepath As String = "C:\Uploads"
Dim uploadedFiles As HttpFileCollection = Request.Files
Dim i As Integer = 0
Do Until i = uploadedFiles.Count
Dim userPostedFile As HttpPostedFile = uploadedFiles(i)
Try
If (userPostedFile.ContentLength> 0) Then
Label1.Text += "<u>File #" & (i + 1) & "</u><br>"
Label1.Text += "File Content Type: " & _
userPostedFile.ContentType & "<br>"
Label1.Text += "File Size: " & _
userPostedFile.ContentLength & "kb<br>"
Label1.Text += "File Name: " & _
userPostedFile.FileName & "<br>"
userPostedFile.SaveAs(filepath & "\" & _
System.IO.Path.GetFileName(userPostedFile.FileName)) Label1.Text += "Location where saved: " & _
filepath & "\" & _ System.IO.Path.GetFileName(userPostedFile.FileName) & _
"<p>"
End If
Catch ex As Exception
Label1.Text += "Error:<br>" & ex.Message
End Try
i += 1
Loop
End Sub
C#
protected void Button1_Click(object sender, EventArgs e)
{
string filepath = "C:\\Uploads";
HttpFileCollection uploadedFiles = Request.Files;
for (int i = 0; i < uploadedFiles.Count; i++)
Continued
Trang 9HttpPostedFile userPostedFile = uploadedFiles[i];
try
{
if (userPostedFile.ContentLength > 0 )
{ Label1.Text += "<u>File #" + (i+1) +
"</u><br>";
Label1.Text += "File Content Type: " + userPostedFile.ContentType + "<br>";
Label1.Text += "File Size: " + userPostedFile.ContentLength + "kb<br>";
Label1.Text += "File Name: " + userPostedFile.FileName + "<br>";
userPostedFile.SaveAs(filepath + "\\" + System.IO.Path.GetFileName(userPostedFile.FileName));
Label1.Text += "Location where saved: " + filepath + "\\" +
System.IO.Path.GetFileName(userPostedFile.FileName) +
"<p>";
} }
catch (Exception Ex)
{
Label1.Text += "Error: <br>" + Ex.Message;
}
}
}
This ASP.NET page enables the end user to select up to three files and click the Upload Files button,
which initializes theButton1_Clickevent Using theHttpFileCollectionclass with theRequest.Files
property lets you gain control over all the files that are uploaded from the page When the files are in this
state, you can do whatever you want with them In this case, the files’ properties are examined and
written to the screen In the end, the files are saved to the Uploads folder in the root directory of the
server The result of this action is illustrated in Figure 3-40
Placing the Uploaded File into a Stream Object
One nice feature of the FileUpload control is that it not only gives you the capability to save the file
to disk, but it also lets you place the contents of the file into aStreamobject You do this by using the
FileContentproperty, as demonstrated in Listing 3-38
Listing 3-38: Uploading the file contents into a Stream object
VB
Dim myStream As System.IO.Stream
myStream = FileUpload1.FileContent
Trang 10System.IO.Stream myStream;
myStream = FileUpload1.FileContent;
Figure 3-40
In this short example, an instance of theStreamobject is created Then, using the FileUpload control’s
FileContentproperty, the content of the uploaded file is placed into the object This is possible because theFileContentproperty returns aStreamobject
Moving File Contents from a Stream Object to a Byte Array
Because you have the capability to move the file contents to aStreamobject of some kind, it is also fairly simple to move the contents of the file to aBytearray (useful for such operations as placing files in a
database of some kind) To do so, first move the file contents to aMemoryStreamobject and then convert the object to the necessaryBytearray object Listing 3-39 shows the process