{"id":170,"date":"2012-04-08T22:12:18","date_gmt":"2012-04-08T14:12:18","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=170"},"modified":"2018-09-03T21:49:13","modified_gmt":"2018-09-03T13:49:13","slug":"how-to-monitor-a-folder-for-new-files-from-your-c-application","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/how-to-monitor-a-folder-for-new-files-from-your-c-application\/","title":{"rendered":"How to monitor a folder for new files from your C# application"},"content":{"rendered":"

Suppose that you need to write a C# application to run in an environment where there are many batch applications running and creating files<\/a> as their output. <\/p>\n

Your application is one of them and is required to process files produced by others. How are you going to know from your C# application when these files are ready?<\/p>\n

In this post, I document the use of a .Net facility that can help you achieve that.<\/p>\n

The FileInputMonitor class<\/h3>\n

Let us create a sample use case. Suppose there is a folder<\/a> which other applications will deposit their file output on a daily basic. The naming convention of the file will be report-for-<CURRENT_DATE-YYYY-MM-DD<\/em>><\/strong>. For instance, on 7th April 2012, the file will be named as report-for-2012-04-07<\/strong>.<\/p>\n

The following FileInputMonitor<\/code> class is an implementation for the sample use case. <\/p>\n

\r\nusing System;\r\nusing System.IO;\r\nusing System.Text;\r\nusing System.Threading;\r\n\r\npublic class FileInputMonitor\r\n{\r\n\r\n    private FileSystemWatcher fileSystemWatcher;\r\n    private string folderToWatchFor \r\n        = AppDomain.CurrentDomain.SetupInformation.ApplicationBase + "toTechcoil";\r\n\r\n    public FileInputMonitor()\r\n    {\r\n\r\n        fileSystemWatcher = new FileSystemWatcher(folderToWatchFor);\r\n        fileSystemWatcher.EnableRaisingEvents = true;\r\n\r\n        \/\/ Instruct the file system watcher to call the FileCreated method\r\n        \/\/ when there are files created at the folder.\r\n        fileSystemWatcher.Created += new FileSystemEventHandler(FileCreated);\r\n\r\n    } \/\/ end FileInputMonitor()\r\n\r\n    private void FileCreated(Object sender, FileSystemEventArgs e)\r\n    {\r\n\r\n        if (e.Name == "report-for-" + System.DateTime.Now.ToString("yyyy-MM-dd")) \r\n        {\r\n            ProcessFile(e.FullPath);\r\n        } \/\/ end if\r\n\r\n    } \/\/ end public void FileCreated(Object sender, FileSystemEventArgs e)\r\n\r\n    private void ProcessFile(String fileName)\r\n    {\r\n        FileStream inputFileStream;\r\n        while (true) \r\n        {\r\n            try\r\n            {\r\n                inputFileStream = new FileStream(fileName, \r\n                    FileMode.Open, FileAccess.ReadWrite);\r\n                StreamReader reader = new StreamReader(inputFileStream);\r\n                Console.WriteLine(reader.ReadToEnd());\r\n                \/\/ Break out from the endless loop\r\n                break;\r\n            }\r\n            catch (IOException)\r\n            {\r\n                \/\/ Sleep for 3 seconds before trying\r\n                Thread.Sleep(3000);\r\n            } \/\/ end try\r\n        } \/\/ end while(true)\r\n    } \/\/ end private void ProcessFile(String fileName)\r\n   \r\n} \/\/ end public class FileInputMonitor\r\n<\/pre>\n
Monitoring whether new files are created in a folder with System.IO.FileSystemWatcher<\/h4>\n
When an instance of FileInputMonitor<\/code> is created, we also create an instance of System.IO.FileSystemWatcher<\/code><\/a> class, passing it the directory path of the folder to monitor. <\/p>\n
After creating an instance of the FileSystemWatcher, we proceed to configure it. In order to enable the FileSystemWatcher<\/code> instance to notify our application when files are created in the folder, we must<\/strong> first set its EnableRaisingEvents<\/code><\/a> property to true.<\/p>\n
We then add a System.IO.FileSystemEventHandler<\/code><\/a> delegate to the Created<\/code><\/a> event so that control can be delegated to the FileCreated<\/code> method of our FileInputMonitor<\/code> class whenever a new file is created. <\/p>\n
Checking whether an expected file is ready for processing<\/h4>\n
When the FileCreated<\/code> method is executed, we check whether the new file is what our application wants via the Name<\/a> property of the System.IO.FileSystemEventArgs<\/code><\/a> instance. If the file is designated for our application, the ProcessFile<\/code> method is called to process the file.<\/p>\n
In the ProcessFile<\/code> method, we attempt to get an instance of System.IO.FileStream<\/code><\/a> with ReadWrite<\/code> access to read from the file<\/a> in an infinite loop. This is because the batch application may still be writing to the file<\/a> when our application received notification of the new file. <\/p>\n
In the event when the instance of FileStream<\/code> cannot be retrieved, the application will wait for 3 seconds via a call to Thread.Sleep<\/a>. Upon success acquisition of the FileStream instance, the code reads from the file, output it to console and break out of the infinite loop.<\/p>\n
Using the FileInputMonitor class<\/h3>\n
To conclude this post, the following is a program that maintains an instance of the FileInputMonitor<\/code> to monitor the toTechcoil<\/strong> folder that is in the same directory as the executable. <\/p>\n
\r\npublic class Program\r\n{\r\n    public static void Main(string[] args)\r\n    {\r\n        FileInputMonitor fileInputMonitor = new FileInputMonitor();\r\n        Console.Read();\r\n    } \/\/ end public static void Main(string[] args)\r\n\r\n} \/\/ end public class Program\r\n<\/pre>\n
Other posts that may interests you<\/h3>\n