Asp.net MVC3扩展之Ajax异常处理特性

      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:

#region AjaxExceptionAttribute
/// <summary>
/// Ajax Exception Handle Attribute
/// </summary>
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class)]
public class AjaxExceptionAttribute : ActionFilterAttribute, IExceptionFilter
{
    /// <summary>
    /// Called when an exception occurs.
    /// </summary>
    /// <param name="filterContext">The filter context.</param>
    public void OnException(ExceptionContext filterContext)
    {
        if (!filterContext.HttpContext.Request.IsAjaxRequest())
            return;

        filterContext.Result = AjaxError(filterContext.Exception.Message, filterContext);

        //Let the system know that the exception has been handled
        filterContext.ExceptionHandled = true;
    }

    /// <summary>
    /// Ajaxes the error.
    /// </summary>
    /// <param name="message">The message.</param>
    /// <param name="filterContext">The filter context.</param>
    /// <returns>JsonResult</returns>
    protected JsonResult AjaxError(string message, ExceptionContext filterContext)
    {
        //If message is null or empty, then fill with generic message
        if (String.IsNullOrEmpty(message))
            message = "Something went wrong while processing your request. Please refresh the page and try again.";

        //Set the response status code to 500
        filterContext.HttpContext.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

        //Needed for IIS7.0
        filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;

        return new JsonResult
        {
            //can extend more properties
            Data = new AjaxExceptionModel () { ErrorMessage = message },
            ContentEncoding = System.Text.Encoding.UTF8,
            JsonRequestBehavior = JsonRequestBehavior.DenyGet
        };
    }
}
#endregion

/// <summary>
/// AjaxExceptionModel
/// </summary>
public class AjaxExceptionModel
{
    /// <summary>
    /// Gets or sets the error message.
    /// </summary>
    /// <value>
    /// The error message.
    /// </value>
    public string ErrorMessage { get; set; }
}

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:

<h4 id="lblMethodError">
</h4>
<br />
<h4 id="lblMethodSuccess">
</h4>
<br />
<h2>ajax post</h2>
<input type="button" value="Post method" id="inputajax1" />
<br />
<input type="button" value="Ajax method with error section" id="inputajax2" />
<p>
    <input type="button" value="Post method for undefined Url" id="inputajax3" />
</p>
<p>
    <input type="button" value="Post method to get Json Result" id="inputajax4" />
</p>
<br />
<h3 id="errorh3info">
</h3>

JQuery的全局AjaxError配置，可参考官方

$("#errorh3info").ajaxError(function (event, request, settings) {
    $(this).append("<li>settings.url:" + settings.url + "</li>");
    $(this).append("<li>request.status:" + request.status + "</li>");
    $(this).append("<li>request.statusText:" + request.statusText + "</li>");

    //request.responseText
    if (request.responseText != "") {
        var jsonValue = jQuery.parseJSON(request.responseText);
        $(this).append("<li>ErrorMessage:" + jsonValue.ErrorMessage + "</li>");
    }
});

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Moq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<HttpRequestBase>();
    mockRequest.SetupGet(http => http.Headers).Returns(header);

    var mockResponse = new Mock<HttpResponseBase>();

    var mockHttpContext = new Mock<HttpContextBase>();
    mockHttpContext.SetupGet(c => c.Request).Returns(mockRequest.Object);
    mockHttpContext.SetupGet(c => c.Response).Returns(mockResponse.Object);

    var context = mockHttpContext.Object;
    var exceptonContextMock = new Mock<ExceptionContext>();
    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。

作者：Petter Liu
出处：http://www.cnblogs.com/wintersun/
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该文章也同时发布在我的独立博客中-Petter Liu Blog。