Posts tagged ASP.NET MVC

When writting web applications, there may be times when you would like to perform some task automatically at the same time or every X number of hours. Web applications only execute their code when a request is made from a client’s browser. Because of this, scheduled tasks within the web application will not work.

There are a few different options:

1. Build a separate Windows Service application that can connect to the assemblies your web application uses to execute the scheduled task.
2. Build a separate Windows application that communicates with a web service that your web application also uses to perform the scheduled task.
3. Use the Windows Scheduler to call the URL of the action to perform the task.

The first option might sound good at first, but creating a separate program that talks to your web application’s library files is a bad idea. Maintenance will become a problem as you change your web application. Since the code is in two places, unit testing will not tell you that the class library you just changed has now broken your scheduled tasks in your windows service. 

The second option is slightly better, but you still may have issues with changing your class library.

The third option is the one that I will show you how to configure. We will setup a VBS script that will perform a call to any web address we pass to it. Then, we’ll setup a batch file that calls the VBS script and passes in one or more URLs to execute. And finally, we’ll go through using the Windows Scheduler to create the scheduled task when the batch file should execute.

The primary advantage to this method is that you get to keep all of your code together in your web application. You simply setup an action that performs whatever task you wish to schedule and make sure that action is callable from an anonymous user.

WebRequest.vbs
You may copy the following code and paste into a text file. Then, rename the file to WebRequest.vbs. The script basically takes an argument that is passed into it as the URL. The HTTP object is setup and then the URL is called using a GET request. Then, the returned status is checked to see if the request was successful or not.

url = WScript.Arguments.Item(0)
'WScript.echo url

set WshShell = WScript.CreateObject("WScript.Shell")
set http = CreateObject("Microsoft.XmlHttp")

http.open "GET", url, FALSE
http.send ""

if (http.Status = 200) then

    WScript.echo "Request successful."

else

    WScript.echo "Error: " & http.Status

end if

set WshShell = nothing
set http = nothing

The Batch File
Calling the WebRequest.vbs file from a batch file is very easy. Simply create a new text file, calling it whatever you’d like, and paste in the following line of text. Rename the file to .BAT when finished.

cscript WebRequest.vbs "http://www.domain.com/controller/action"

Scheduling The Task
From your Windows server, open the Control Panel and then open the Scheduled Tasks item. Next, click on Add Scheduled Task. Choose any application to schedule.  This will be changed later on. Configure how often you wish the schedule to run and enter a user name and password to run the schedule as. This users should have access to running the web browser from the server.

After your new scheduled task has been created, open it. In the Run text box, type in the full path to your batch file. Then, in the Start In text box, type in the full path without the batch file name. You can also adjust your scheduled time from within here. Click OK to save the changes and your scheduled task should be ready.

You can test the Windows Scheduler by setting the scheduled time to a minute or two in the future and then waiting for it to execute. If you just wish to test your action, or manually run it, you can simply run the batch file.