By John Peterson
As is usually the case for me, the idea for this article came from a project on which I was recently working. Without going into all the gory the details, the basic requirement was that something needed to happen on a daily basis. This obviously wasn’t the first time I’d run into this type of requirement, but as I started digging up my normal solution, I realized that while it was tried and true, it was also horribly outdated. It was written as a .vbs file designed to run via WSH. This meant that while it was easy to make changes to the script because it was written in plain text and not compiled, making sure those changes worked correctly and debugging new versions of the script ranged from slightly annoying to downright frustrating.
Note: For those of you who would like to learn more about the old system I had been using to schedule script execution, I wrote up the concepts involved in an old article over on ASP 101: Getting Scripts to Run on a Schedule. The actual processing involved had evolved over the years and obviously varied based on the project, but the basic process of scheduling a .vbs file that is outlined in method three of that article had pretty much remained the same.
Thinking there had to be a better way, I set out to build a command-line .NET application that I could then schedule via Windows Scheduled Tasks. Not only would this allow me to utilize the power of the .NET Framework, but it would also allow me to more easily test and debug the application. In this article, I’ll walk you through the process of building a simple .NET command-line application that is designed to be scheduled to execute. For the sake of illustration, the sample application will send an HTTP request to a web server and send the returned HTML as the body of an email message.
If you don’t already have a version of Visual Studio that can build a command line application, you’ll need to download and install the Express Edition product of your choice:
You’ll only need one and I recommend and will be using Visual Basic 2008 Express Edition for the remainder of this article. The code will obviously be different if you choose a different language, but the concepts are pretty much the same.
For those of you already using Visual Web Developer 2008 Express Edition, don’t worry… it’s perfectly acceptable to have multiple Express Edition products installed.
Building the Command-Line Application
The sample application I’m going to build will send an HTTP request to a web server. It will then take the HTML returned from the server and use it as the body of an email message. The code is pretty simple and can be changed to do whatever your situation requires. The steps involved are pretty much the same regardless of what the code involved actually does.
Once you’ve got Visual Basic 2008 Express Edition installed and working, launch it and select
File -> New Project. This will bring up the “New Project” dialog box.
You want to select “Console Application” and give your application a meaningful name. I’m calling the sample application “Http2Email”. Once you click “OK”, your workspace should look something like this:
Since I like my objects to have meaningful names, the first thing I’ll do is rename “Module1.vb” to “Http2Email.vb” in the “Solution Explorer” pane. This will update the name in all the appropriate places in the project. After which, I’ll save the project to disk by doing a
File -> Save All...
Next I’m going to change a few settings. If you double-click on the “My Project” item in “Solution Explorer”, you’ll get a configuration screen that looks like this:
Since a number of my Web servers are still running .NET 2.0, the first setting I’ll change is the target framework version. On the “Compile” tab, click the “Advanced Compile Options…” button. The bottom option in the resulting dialog box is “Target framework”. Change it to “.NET Framework 2.0”.
On the “References” tab, we can remove a bunch of the references and imported namespaces. Remove all but the “System” reference (unless you’re building a different application and need other references) and all the “Imported Namespaces” except for: Microsoft.VisualBasic, System, System.Collections, and System.Collections.Generic.
Next I’m going to define some application settings. By defining these as settings instead of hard-coding them, we can change the application’s parameters and hence its behavior without needing to recompile it. On the “Settings” tab, I define eight application-scoped settings:
|Url||URL from which we pull the HTML to use as the body of the email|
|EmailFrom||From email address(es)|
|EmailTo||To email address(es)|
|EmailCC||CC email address(es)|
|EmailBCC||BCC email address(es)|
|EmailSubject||Subject line for the email message|
|EmailHtml||Boolean indicating if the email should be formatted as HTML or not|
|SmtpServer||Name of the SMTP server to use to send the email message|
They’re pretty straight-forward. I’ve included the values I used to test with in the image above, but you’ll obviously want to use your own settings for the URL, email addresses, and SMTP server.
The only setting that is a little interesting is the “EmailSubject”. If you look at the value, you’ll notice that I’ve included the phrase “<date>” as a place holder. The application’s code replaces that with the current date. I only did this as an illustration of how you can use the setting functionality and yet still provide for dynamically changing values.
Now that we’ve got the application all configured, it’s time to add the code. It’s probably easiest it you just cut and paste the code from the box below:
Dim myWebRequest As WebRequest
Dim myStreamReader As StreamReader
Dim strSubject, strBody As String
Dim myMailMessage As Mail.MailMessage
Dim mySmtpClient As Mail.SmtpClient
' Retrieve HTML via HTTP request to use as body of email
myWebRequest = WebRequest.Create(My.Settings.Url)
myStreamReader = New StreamReader(myWebRequest.GetResponse().GetResponseStream())
strBody = myStreamReader.ReadToEnd
' Get subject from settings and replace placeholder with current date
strSubject = My.Settings.EmailSubject
strSubject = strSubject.Replace("<date>", FormatDateTime(Now(), DateFormat.ShortDate))
' Create email message
myMailMessage = New Mail.MailMessage(My.Settings.EmailFrom, My.Settings.EmailTo, strSubject, strBody)
If My.Settings.EmailCC <> "" Then myMailMessage.CC.Add(My.Settings.EmailCC)
If My.Settings.EmailBCC <> "" Then myMailMessage.Bcc.Add(My.Settings.EmailBCC)
myMailMessage.IsBodyHtml = My.Settings.EmailHtml
' Send email
mySmtpClient = New Mail.SmtpClient()
mySmtpClient.Host = My.Settings.SmtpServer
The code is pretty simple so I won’t spend too much time going over it. The only thing that might seem a little odd to those of you who aren’t used to it is all the references to My.Settings. That’s the namespace used to access the settings we defined previously.
At this point you can go ahead and build and run the application from within the development environment to make sure everything is working. You can do this by either click
Debug -> Start Debugging or pressing the “F5” key.
If you get an error it’ll probably be related to either a bad URL or an unreachable or locked down SMTP server. To resolve the later, you might need to set credentials on the SMTP client object.
If you don’t get an error, you’ll most likely just see a black console window open for a second and then go away. That’s exactly what we want to happen. Since the application is designed to run when no one is logged on, it doesn’t really provide any visual feedback. Simply wait a few minutes for the email to make its way through the network and to your Inbox.
Once you’ve got your application working to your satisfaction, from the Build menu select
Build -> Build Http2Email. Then you’ll find the executable and config files in the “bin\Release” sub-folder of your project’s folder.
These are the files you’ll need to copy to whatever computer on which you want to schedule the application to run.
Remember those settings we defined earlier. If you open up the “Http2Email.exe.config” file with Notepad and scroll to the bottom of the file, you’ll see all those settings and values stored in XML format. If you need to modify one for testing or if you need to change a setting later, simply edit the text file and the next time the application runs it will read in the new value. No need to fire off Visual Studio or recompile anything. Pretty slick, huh?
Before we move on to the scheduling part of the article, I want to re-iterate that although our application simply does an HTTP request and sends an email, you’re free to do whatever you want to in your console application. You’ve got full access to the .NET Framework and are pretty much limited only by the lack of a graphical UI.
Scheduling the Application to Run
Now that our command-line application is working the way we want it to, the next step is to get it scheduled to run at the right time. As I mentioned previously, the first step is to copy the executable and configuration files to the target computer. Where you store them is up to you, but It’s probably best if you give them their own folder. I put them in a “schedule” folder under my server’s “Inetpub” folder since they’re related to my web application, but I want to keep them outside of the “wwwroot” folder.
If you’re logged into the server interactively, once you’ve copied the file, you can simply double-click on the executable to see if it runs without generating an error. If it does, all that remains is to set up a scheduled task.
To set a program to run as a scheduled task, you need to go to the “Scheduled Tasks” Control Panel applet. You can usually get there via
Start -> Control Panel -> Scheduled Tasks.
Once there you should see an item that says “Add Scheduled Task” along with any other tasks with may already be scheduled. If you double-click “Add Scheduled Task”, it will launch the “Scheduled Task Wizard”.
Click the “Browse” button to find and select the application’s executable file (“Http2Email.exe”).
Select the type of schedule and set the details telling the computer when it should run the application.
It’ll then ask you for a username and password for the account as which it should run the application.
Click the “Finish” button and the new task should appear in the “Scheduled Tasks” window. From here you can monitor the task and even see the return result from the last time the application ran (0x0 indicates the application exited without generating an error… anything else usually means there was an error).
I hope this article has shown you just how easy it is to build a command-line .NET application and schedule it to run via Windows Scheduled Tasks. If you’re used to building web-based applications, it may feel a little weird at first, but after you’ve done it a couple times you’ll get the hang of things and realize how much flexibility it actually gives you to do things on your schedule.