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   源码介绍

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using System;
using System.Data;
using System.Data.SqlClient;
using System.Security.Principal;
using System.Threading;
using System.Net;
using System.Diagnostics;
using System.Collections;
using System.ComponentModel;
using System.Web;
using System.Web.Mail;
using System.Web.Caching;
using System.Web.SessionState;
using System.IO;
using System.Messaging;

namespace TestCacheTimeout 
{
	/// <summary>
	/// Summary description for Global.
	/// </summary>
	public class Global : System.Web.HttpApplication
	{
		private const string DummyPageUrl = "http://localhost/TestCacheTimeout/WebForm1.aspx";
		private const string CONNECTION_STRING = "Data Source=(local);Initial Catalog=tempdb;Integrated Security=SSPI;";
		private const string LOG_FILE = @"c:\temp\Cachecallback.txt";
		private const string MSMQ_NAME = ".\\private$\\ASPNETService";
		private const string DummyCacheItemKey = "GagaGuguGigi";

		public static ArrayList _JobQueue = new ArrayList();

		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.IContainer components = null;

		public Global()
		{
			InitializeComponent();
		}	
		
		protected void Application_Start(Object sender, EventArgs e)
		{
			RegisterCacheEntry();
		}

		/// <summary>
		/// Register a cache entry which expires in 1 minute and gives us a callback.
		/// </summary>
		/// <returns></returns>
		private void RegisterCacheEntry()
		{	
			// Prevent duplicate key addition
			if( null != HttpContext.Current.Cache[ DummyCacheItemKey ] ) return;

			HttpContext.Current.Cache.Add( DummyCacheItemKey, "Test", null, DateTime.MaxValue,
				TimeSpan.FromMinutes(1), CacheItemPriority.NotRemovable,
				new CacheItemRemovedCallback( CacheItemRemovedCallback ) );
		}

		/// <summary>
		/// Callback method which gets invoked whenever the cache entry expires.
		/// We can do our "service" works here.
		/// </summary>
		/// <param name="key"></param>
		/// <param name="value"></param>
		/// <param name="reason"></param>
		public void CacheItemRemovedCallback(
			string key,
			object value,
			CacheItemRemovedReason reason
			)
		{
			Debug.WriteLine("Cache item callback: "   DateTime.Now.ToString() );

			// Do the service works
			DoWork();

			// We need to register another cache item which will expire again in one
			// minute. However, as this callback occurs without any HttpContext, we do not
			// have access to HttpContext and thus cannot access the Cache object. The
			// only way we can access HttpContext is when a request is being processed which
			// means a webpage is hit. So, we need to simulate a web page hit and then 
			// add the cache item.
			HitPage();
		}

		/// <summary>
		/// Hits a local webpage in order to add another expiring item in cache
		/// </summary>
		private void HitPage()
		{
			WebClient client = new WebClient();
			client.DownloadData(DummyPageUrl);
		}

		/// <summary>
		/// Asynchronously do the 'service' works
		/// </summary>
		private void DoWork()
		{
			Debug.WriteLine("Begin DoWork...");
			Debug.WriteLine("Running as: "   WindowsIdentity.GetCurrent().Name );

			DoSomeFileWritingStuff();
			DoSomeDatabaseOperation();
			DoSomeEmailSendStuff();
			DoSomeMSMQStuff();
			ExecuteQueuedJobs();

			Debug.WriteLine("End DoWork...");
		}

		/// <summary>
		/// Execute jobs that are queued for execution at a specific time
		/// </summary>
		private void ExecuteQueuedJobs()
		{
			ArrayList jobs = new ArrayList();

			// Collect which jobs are overdue
			foreach( Job job in _JobQueue )
			{
				if( job.ExecutionTime <= DateTime.Now )
					jobs.Add( job );
			}

			// Eecute the jobs that are overdue
			foreach( Job job in jobs )
			{
				lock( _JobQueue )
				{
					_JobQueue.Remove( job );
				}

				job.Execute();
			}
		}

		/// <summary>
		/// Test file write. Make sure the path allows ASPNET or NETWORK SERVICE account
		/// to write 
		/// </summary>
		private void DoSomeFileWritingStuff()
		{
			Debug.WriteLine("Writing to file...");

			try
			{
				using( StreamWriter writer = new StreamWriter(LOG_FILE, true) )
				{
					writer.WriteLine("Cache Callback: {0}", DateTime.Now);
					writer.Close();
				}
			}
			catch( Exception x )
			{
				Debug.WriteLine( x );
			}

			Debug.WriteLine("File write successful");
		}

		/// <summary>
		/// Test database connectivity
		/// </summary>
		private void DoSomeDatabaseOperation()
		{
			Debug.WriteLine("Connecting to database...");

			using( SqlConnection con = new SqlConnection(CONNECTION_STRING) )
			{
				con.Open();

				using( SqlCommand cmd = new SqlCommand( "INSERT INTO ASPNETServiceLog VALUES (@Message, @DateTime)", con ) )
				{
					cmd.Parameters.Add("@Message", SqlDbType.VarChar, 1024).Value = "Hi I'm the ASP NET Service";
					cmd.Parameters.Add("@DateTime", SqlDbType.DateTime).Value = DateTime.Now;

					cmd.ExecuteNonQuery();
				}

				con.Close();
			}

			Debug.WriteLine("Database connection successful");
		}
 
		/// <summary>
		/// Test email send
		/// </summary>
		private void DoSomeEmailSendStuff()
		{
			try
			{
				MailMessage msg = new MailMessage();
				msg.From = "abc@cde.fgh";
				msg.To = "ijk@lmn.opq";
				msg.Subject = "Reminder: "   DateTime.Now.ToString();
				msg.Body = "This is a server generated message";
			
				SmtpMail.Send( msg );
			}
			catch( Exception x )
			{
				Debug.WriteLine( x );
			}
		}

		/// <summary>
		/// Test MSMQ
		/// </summary>
		private void DoSomeMSMQStuff()
		{
			using( MessageQueue queue = new MessageQueue(MSMQ_NAME) )
			{
				queue.Send(DateTime.Now);
				queue.Close();
			}
		}

		protected void Session_Start(Object sender, EventArgs e)
		{

		}

		protected void Application_BeginRequest(Object sender, EventArgs e)
		{
			// If the dummy page is hit, then it means we want to add another item
			// in cache
			if( HttpContext.Current.Request.Url.ToString() == DummyPageUrl )
			{
				// Add the item in cache and when succesful, do the work.
				RegisterCacheEntry();
			}
		}

		protected void Application_EndRequest(Object sender, EventArgs e)
		{

		}

		protected void Application_AuthenticateRequest(Object sender, EventArgs e)
		{

		}

		protected void Application_Error(Object sender, EventArgs e)
		{
			Debug.WriteLine( Server.GetLastError() );
		}

		protected void Session_End(Object sender, EventArgs e)
		{

		}

		protected void Application_End(Object sender, EventArgs e)
		{

		}
			
		#region Web Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{    
			this.components = new System.ComponentModel.Container();
		}
		#endregion
	}
}