ASP.NET MVC 通过ActionFilter 实现AOP设计 示例

在Asp.Net MVC 框架中我们可以通过ActionFilter来拦截请求，并对请求做一定处理后再交于Action做数据处理。此外，也可以利用ActionFilter来对Action的返回值做统一处理，再返回给客户端调用。同ActionFilter的合理利用，能够很容易实现AOP设计，达到代码隔离的效果。 在这里分享一个示例，以供交流学习。

在该示例中，实现了 数据流拦截 和 参数的注入。

public class MyIntercepterAttribute : FilterAttribute, IActionFilter
{
private const string nodeName = "someNode";
public void OnActionExecuting(ActionExecutingContext actionContext)
{
var inputStream = actionContext.HttpContext.Request.InputStream;
inputStream.Position = 0;
string payloadStr;
using (var streamReader = new StreamReader(inputStream))
{//读取原有数据
payloadStr = streamReader.ReadToEnd();
}

if (string.IsNullOrWhiteSpace(payloadStr))
{
throw new HttpException(400, "Invalid payload");
}

var wrapper = (JObject)JsonConvert.DeserializeObject(payloadStr);
var originalDataNode = wrapper[nodeName];

if (originalDataNode == null)
{
throw new HttpException(400, "Invalid schema.");
}

//将原始字符串解析为Json 数据方便做进一步处理。
var plainRequest = originalDataNode.ToObject<string>();
var requestRootNode = (JObject)JsonConvert.DeserializeObject(plainRequest);

var parameters = actionContext.ActionDescriptor.GetParameters();
var jsonSerializer = new JsonSerializer { ContractResolver = new CamelCasePropertyNamesContractResolver() };
foreach (var param in parameters)
{//根据需求 构造/转化 Action 的参数
JToken matchedParamNode;
requestRootNode.TryGetValue(param.ParameterName, StringComparison.CurrentCultureIgnoreCase, out matchedParamNode) ;
if (matchedParamNode != null)
{
actionContext.ActionParameters[param.ParameterName] = matchedParamNode.ToObject(param.ParameterType, jsonSerializer);
}
else if (param.ParameterType.IsClass && param.ParameterType != typeof(string))
{
actionContext.ActionParameters[param.ParameterName] = requestRootNode.ToObject(param.ParameterType, jsonSerializer);
}
}
}

public void OnActionExecuted(ActionExecutedContext filterContext)
{
var result = filterContext.Result;
if (result is JsonResult)
{//转换 Action的返回值
var jsonResult = result as JsonResult;
var handledResponse = JsonConvert.SerializeObject(jsonResult.Data);

jsonResult.Data = new { Result = handledResponse };
}
else
{
throw new  NotImplementedException("Currently, this sample only support json result.");
}
}
}