MVC Tutorial Nine: Exception Filters

We usually add try-catch-finally code in order to catch exceptions in the program, but this will make the program code look huge. In MVC, we can use exception filters to catch exceptions in the program, as shown in the following figure :

After using the exception filter, we don't need to write the exception handling code such as Try-Catch-Finally in the Action method, but leave this work to HandleError. This feature can also be applied to the Controller, or Applied to the Action aspect.

Notice:

When using an exception filter, the value of the attribute mode of the customErrors configuration section must be On.

Demonstration example:

1. The Error controller code is as follows:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Web;
 5 using System.Web.Mvc;
 6 using System.Data.SqlClient;
 7 using System.IO;
 8 
 9 namespace _3_异常过滤器.Controllers
10 {
11     public class ErrorController : Controller
12     {
13         // GET: Error
14         [HandleError(ExceptionType =typeof(ArithmeticException),View ="Error")]
15         public ActionResult Index(int a,int b)
16         {
17             int c = a / b;
 18              ViewData["Result"] = c;
 19              return View();
 20          }
 21  
22          /// < summary > 
23          /// Test database exception
 24          /// </ summary > 
25          / // < returns ></ returns > 
26          [HandleError(ExceptionType = typeof(SqlException), View = "Error")]
 27          public ActionResult DbError()
 28          {
 29              // Bad connection string
 30             SqlConnection conn = new SqlConnection(@"Initial Catalog=StudentSystem; Integrated Security=False;User Id=sa;Password=******;Data Source=127.0.0.1");
31             conn.Open();
32             // 返回Index视图
33             return View("Index");
34         }
35 
36         /// <summary>
37         /// IO异常
38         /// </summary>
39         /// <returns></returns>
40         [HandleError(ExceptionType = typeof(IOException), View = "Error")]
41          public ActionResult IOError()
 42          {
 43              // Access a non-existing file
 44              System.IO.File.Open(@"D:\error.txt",System.IO.FileMode.Open);
 45              // Return Index View
 46              return View("Index");
 47          }
 48      }
 49 }

 2. The routing configuration is as follows:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Web;
 5 using System.Web.Mvc;
 6 using System.Web.Routing;
 7 
 8 namespace _3_异常过滤器
 9 {
10     public class RouteConfig
11     {
12         public static void RegisterRoutes(RouteCollection routes)
13         {
14             routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
15 
16             routes.MapRoute(
17                 name: "Default",
18                 url: "{controller}/{action}/{id}",
19                 defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
20             );
21 
22             // 新增路由配置
23             routes.MapRoute(
24               name: "Default2",
25               url: "{controller}/{action}/{a}/{b}",
26               defaults: new { controller = "Home", action = "Index", a=0,b=0 }
27           );
28         }
29     }
30 }

 3. The configuration file is as follows:

<system.web>
    <compilation debug="true" targetFramework="4.6.1" />
    <httpRuntime targetFramework="4.6.1" />
    <httpModules>
      <add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" />
    </httpModules>
    <!--customErrors configuration section mode attribute value must be On-->
    <customErrors mode="On">     
    </customErrors>
</system.web>

4. Running results

URL：http://localhost:21868/error/index/8/4

result:

URL：http://localhost:21868/error/index/8/0

result:

URL：http://localhost:21868/error/DbError

result:

URL：http://localhost:21868/error/IOError

result:

Multiple exceptions can be handled through HandleError on the same controller or Action method, and the order of capture is determined through the Order property, but the top exception must be the same level or subclass of the following exception. As shown below:

The above program can be modified into the following code:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Web;
 5 using System.Web.Mvc;
 6 using System.Data.SqlClient;
 7 using System.IO;
 8 
 9 namespace _3_异常过滤器.Controllers
10 {
11     [HandleError(Order =1, ExceptionType = typeof(SqlException), View = "Error")]
12     [HandleError(Order =2, ExceptionType = typeof (IOException), View = " Error " )]
 13      [HandleError(Order = 3 )] // If View is not specified, it will jump to the Error view under Share by default 
14      public  class ErrorController : Controller
 15      {
 16          public ActionResult Index( int a, int b)
 17          {
 18              int c = a / b;
 19              ViewData[ " Result " ] = c;
 20              return View();
 21         }
 22  
23          ///  <summary> 
24          /// Test database exception
 25          ///  </summary> 
26          ///  <returns></returns> 
27          public ActionResult DbError()
 28          {
 29              // Bad connection character String 
30              SqlConnection conn = new SqlConnection( @" Initial Catalog=StudentSystem; Integrated Security=False;User Id=sa;Password=******;Data Source=127.0.0.1 " );
 31              conn.Open();
 32              // Return to Index view 
33              return View(" Index " );
 34          }
 35  
36          ///  <summary> 
37          /// IO exception
 38          ///  </summary> 
39          ///  <returns></returns> 
40          public ActionResult IOError()
 41          {
 42              / / Access a file that does not exist 
43              System.IO.File.Open( @" D:\error.txt " ,System.IO.FileMode.Open);
 44              // Return to the Index view 
45              return View( " Index " );
 46          }
47     }
48 }