命令过滤器

关键字: 命令过滤器, 命令, 过滤器, OnCommandExecuting, OnCommandExecuted

SuperSocket 中的命令过滤器看起来有些像 ASP.NET MVC 中的 Action Filter，你可以用它来做命令执行的拦截，命令过滤器会在命令执行前和执行后被调用。

命令过滤器必须继承于 Attribute 类 CommandFilterAttribute:

  1.  /// <summary>
  2. /// Command filter attribute
  3. /// </summary>
  4. [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
  5. public abstract class CommandFilterAttribute : Attribute
  6. {
  7.     /// <summary>
  8.     /// Gets or sets the execution order.
  9.     /// </summary>
  10.     /// <value>
  11.     /// The order.
  12.     /// </value>
  13.     public int Order { get; set; }
  15.     /// <summary>
  16.     /// Called when [command executing].
  17.     /// </summary>
  18.     /// <param name="commandContext">The command context.</param>
  19.     public abstract void OnCommandExecuting(CommandExecutingContext commandContext);
  21.     /// <summary>
  22.     /// Called when [command executed].
  23.     /// </summary>
  24.     /// <param name="commandContext">The command context.</param>
  25.     public abstract void OnCommandExecuted(CommandExecutingContext commandContext);
  26. }

你需要为你的命令过滤器实现下面两个方法:

OnCommandExecuting: 此方法将在命令执行前被调用;

OnCommandExecuted: 此方法将在命令执行后被调用;

Order: 此属性用于设置多个命令过滤器的执行顺序;

下面的代码定义了一个命令过滤器 LogTimeCommandFilterAttribute 用于记录执行时间超过5秒钟的命令:

  1. public class LogTimeCommandFilter : CommandFilterAttribute
  2. {
  3.     public override void OnCommandExecuting(CommandExecutingContext commandContext)
  4.     {
  5.         commandContext.Session.Items["StartTime"] = DateTime.Now;
  6.     }
  8.     public override void OnCommandExecuted(CommandExecutingContext commandContext)
  9.     {
  10.         var session = commandContext.Session;
  11.         var startTime = session.Items.GetValue<DateTime>("StartTime");
  12.         var ts = DateTime.Now.Subtract(startTime);
  14.         if (ts.TotalSeconds > 5 && session.Logger.IsInfoEnabled)
  15.         {
  16.             session.Logger.InfoFormat("A command '{0}' took {1} seconds!", commandContext.CurrentCommand.Name, ts.ToString());
  17.         }
  18.     }
  19. }

然后通过增加属性的方法给命令 "QUERY" 应用此过滤器:

  1. [LogTimeCommandFilter]
  2. public class QUERY : StringCommandBase<TestSession>
  3. {
  4.     public override void ExecuteCommand(TestSession session, StringCommandInfo commandData)
  5.     {
  6.         //Your code
  7.     }
  8. }

如果你想应用次过滤器给所有的命令, 你可以向下面的代码这样将此命令过滤器的属性加到你的 AppServer 类上面去:

  1. [LogTimeCommandFilter]
  2. public class TestServer : AppServer<TestSession>
  3. {
  5. }

你可以通过将 commandContext's 的 Cancel 属性设为 True 来取消当前命令的执行:

  1. public class LoggedInValidationFilter : CommandFilterAttribute
  2. {
  3.     public override void OnCommandExecuting(CommandExecutingContext commandContext)
  4.     {
  5.         var session = commandContext.Session as MyAppSession;
  7.         //If the session is not logged in, cancel the executing of the command
  8.         if (!session.IsLoggedIn)
  9.             commandContext.Cancel = true;
  10.     }
  12.     public override void OnCommandExecuted(CommandExecutingContext commandContext)
  13.     {
  15.     }
  16. }