在Asp.net MVC 3 Web开发中，我们会大量使用各种ajax请求，针对ajax请求如何结何server端如何做异常处理呢？我们可以扩展ActionFilterAttribute，实现一个Ajax异常处理特性。假设您是使用JQuery脚本开发来实现Ajax，看代码:
1: #region AjaxExceptionAttribute
2: ///
3: /// Ajax Exception Handle Attribute
4: ///
5: [AttributeUsage(AttributeTargets.Method | AttributeTargets.Class)]
6: public class AjaxExceptionAttribute : ActionFilterAttribute, IExceptionFilter
7: { 8: ///
9: /// Called when an exception occurs.
10: ///
11: /// The filter context.
12: public void OnException(ExceptionContext filterContext)
13: { 14: if (!filterContext.HttpContext.Request.IsAjaxRequest())
15: return;
16:
17: filterContext.Result = AjaxError(filterContext.Exception.Message, filterContext);
18:
19: //Let the system know that the exception has been handled
20: filterContext.ExceptionHandled = true;
21: }
22:
23: ///
24: /// Ajaxes the error.
25: ///
26: /// The message.
27: /// The filter context.
28: ///JsonResult
29: protected JsonResult AjaxError(string message, ExceptionContext filterContext)
30: { 31: //If message is null or empty, then fill with generic message
32: if (String.IsNullOrEmpty(message))
33: message = "Something went wrong while processing your request. Please refresh the page and try again.";
34:
35: //Set the response status code to 500
36: filterContext.HttpContext.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
37:
38: //Needed for IIS7.0
39: filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;
40:
41: return new JsonResult
42: { 43: //can extend more properties
44: Data = new AjaxExceptionModel () { ErrorMessage = message }, 45: ContentEncoding = System.Text.Encoding.UTF8,
46: JsonRequestBehavior = JsonRequestBehavior.DenyGet
47: };
48: }
49: }
50: #endregion
51:
52: ///
53: /// AjaxExceptionModel
54: ///
55: public class AjaxExceptionModel
56: { 57: ///
58: /// Gets or sets the error message.
59: ///
60: ///
61: /// The error message.
62: ///
63: public string ErrorMessage { get; set; } 64: }
代码已有相关注释。AjaxExceptionModel您完全可以自定义更多的属性，然后在Controller或Action上增加这个特性。 像下面这个HomeController有一个YouKnow的Action，这里为演示我们故意throw一个Exception:
[AjaxException]
public class HomeController : BaseController
{ [HttpPost]
public ActionResult YouKnow(FormCollection fc)
{ throw new ArgumentNullException("YouKnow method: fc should not be null"); }
}
接下来看HTML与JQuery:
ajax post
$("#errorh3info").ajaxError(function (event, request, settings) { $(this).append("$(this).append("$(this).append("//request.responseText
if (request.responseText != "") { var jsonValue = jQuery.parseJSON(request.responseText);
$(this).append("}
});
给button增加一个Post请求：
$('#inputajax1').click(function () { $.post('/Home/YouKnow/' , { id: 1 } , function (data) { $('div#right-box.data').html(data); });
});
这时View上将显示, 我们将看到ErrorMessage是JSON对象的属性：
settings.url:/Home/YouKnow/ request.status:500 request.statusText:error ErrorMessage:Value cannot be null. Parameter name: YouKnow method: fc should not be null
当然也可以这样:
//ajax post when throw an exception at server side
$('#inputajax2').click(function () { $.ajax({ type: "POST",
url: "/Home/YouKnow2",
data: "fail=1",
dataType: "json",
error: function (xhr, status, error) { // Show the error
$('#lblMethodError').append(xhr.responseText); $('#lblMethodError').show(); },
success: function (data, textSuccess) { // show the success message
$('#lblMethodSuccess').show(); }
});
});
这时View上，比上面那个请求多显示一条信息, 这是因为我们这里定义了自己error处理callback.
{"ErrorMessage":"Value cannot be null.\r\nParameter name: YouKnow method: fc should not be null"}
当我们请求一个不存在Action时呢:
//request undefined url
$('#inputajax3').click(function () { $.post('/Home/YouKnow2233/' , { id: 1 } , function (data) { $('div#right-box.data').html(data); });
});
页面上将显示： settings.url:/Home/YouKnow2233/ request.status:0 request.statusText:error
最后我们来看这个ActionFilter的单元测试，这里使用类库:
[TestMethod]
public void Test_Native_AjaxExceptionAttribute()
{ //arrange
var header = new System.Collections.Specialized.NameValueCollection();
header.Add("X-Requested-With", "XMLHttpRequest"); var mockRequest = new Mock();
mockRequest.SetupGet(http => http.Headers).Returns(header);
var mockResponse = new Mock();
var mockHttpContext = new Mock();
mockHttpContext.SetupGet(c => c.Request).Returns(mockRequest.Object);
mockHttpContext.SetupGet(c => c.Response).Returns(mockResponse.Object);
var context = mockHttpContext.Object;
var exceptonContextMock = new Mock();
exceptonContextMock.SetupGet(ac => ac.HttpContext).Returns(context);
string errorStr="error";
exceptonContextMock.SetupGet(ec => ec.Exception).Returns(new AggregateException(errorStr));
//act
var ajaxAttribute = new AjaxExceptionAttribute();
var exceptionContext = exceptonContextMock.Object;
ajaxAttribute.OnException(exceptionContext);
//verify
mockRequest.VerifyAll();
mockResponse.VerifyAll();
mockHttpContext.VerifyAll();
exceptonContextMock.VerifyAll();
//assert
var jsonResult = exceptionContext.Result as JsonResult;
Assert.IsNotNull(jsonResult.Data);
Assert.IsTrue(exceptionContext.HttpContext.Request.IsAjaxRequest());
Assert.AreEqual((jsonResult.Data as AjaxExceptionModel).ErrorMessage, errorStr);
Assert.AreEqual(JsonRequestBehavior.DenyGet, jsonResult.JsonRequestBehavior);
Assert.AreEqual(typeof(AggregateException), exceptionContext.Exception.GetType());
}
上面的UnitTest我们Mock HttpContext,HttpRequest,HttpResponse来实现对ActionFilter的测试。 希望您Web开发有帮助。
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