特性是什么

特性（Attribute）是用于在运行时传递程序中各种元素（比如类、方法、结构、枚举、组件等）的行为信息的声明性标签。说白了它只是继承了Attrbute的一个类。

实际使用

这边做一个调用接口开始和结束写入日志的应用

public class HelpAttribute : ActionFilterAttribute
{
    public HelpAttribute() { }

    private string requestFilter1 = string.Empty;

    /// <summary>
    /// 过滤字段1
    /// </summary>
    public string RequestFilter1
    {
        get
        {
            return requestFilter1;
        }

        set
        {
            requestFilter1 = value;
        }
    }

    private string requestFilter2 = string.Empty;
    /// <summary>
    /// 过滤字段2
    /// </summary>
    public string RequestFilter2
    {
        get
        {
            return requestFilter2;
        }

        set
        {
            requestFilter2 = value;
        }
    }

    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        base.OnActionExecuting(actionContext);
        try
        {
            WriteRequestLog(actionContext);
        }
        catch
        {

        }

    }

    public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
    {
        base.OnActionExecuted(actionExecutedContext);

        try
        {
            WriteResponseLog(actionExecutedContext);
        }
        catch
        {

        }
    }
    log4net.ILog log = log4net.LogManager.GetLogger("testApp.Logging");
    private void WriteRequestLog(HttpActionContext actionContext)
    {
        var stopWatch = new Stopwatch();
        stopWatch.Start();

        //控制器名
        string controlName = actionContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        //Action名
        string actName = actionContext.ActionDescriptor.ActionName;
        //过滤字段1
        string valFilter1 = string.Empty;
        //过滤字段2
        string valFilter2 = string.Empty;

        string requestContent = string.Empty;
        string requestUrl = actionContext.Request.RequestUri.ToString();

        var sm = HttpContext.Current.Request.InputStream;
        sm.Seek(0, SeekOrigin.Begin);
        byte[] data = new byte[sm.Length];
        sm.Read(data, 0, data.Length);
        requestContent = Encoding.UTF8.GetString(data);
        if (!string.IsNullOrEmpty(requestContent))
        {
            JObject reqJobject = JObject.Parse(requestContent);
            if (!string.IsNullOrEmpty(RequestFilter1))
                valFilter1 = reqJobject[RequestFilter1]?.ToString();
            if (!string.IsNullOrEmpty(RequestFilter2))
            {
                string _inputtext = reqJobject["InputText"]?.ToString();
                JObject jo2 = JObject.Parse(_inputtext);
                valFilter2 = jo2[RequestFilter2]?.ToString();
            }
        }

        HttpContext.Current.Items["controlName"] = controlName;
        HttpContext.Current.Items["actName"] = actName;
        HttpContext.Current.Items["valFilter1"] = valFilter1;
        HttpContext.Current.Items["valFilter2"] = valFilter2;
        HttpContext.Current.Items["stopWatch"] = stopWatch;

        Task.Run(() =>
        {
            string msg = string.Format("请求开始，控制器名称：{0}，方法名：{1}，来源渠道：{2}，单号：{3}，请求内容：{4}", controlName, actName, valFilter1, valFilter2, requestContent);
            log.Info(msg);
        });
    }


    private void WriteResponseLog(HttpActionExecutedContext actionExecutedContext)
    {
        //控制器名
        string controlName = HttpContext.Current.Items["controlName"]?.ToString();
        //Action名
        string actName = HttpContext.Current.Items["actName"]?.ToString();
        //过滤字段1
        string valFilter1 = HttpContext.Current.Items["valFilter1"]?.ToString();
        //过滤字段2
        string valFilter2 = HttpContext.Current.Items["valFilter2"]?.ToString();

        string timespend = string.Empty;

        Stopwatch sw = HttpContext.Current.Items["stopWatch"] as Stopwatch;
        if (sw != null)
        {
            sw.Stop();
            timespend = sw.ElapsedMilliseconds.ToString();
        }

        Task.Run(() =>
        {
            string responseContent = actionExecutedContext.Response.Content.ReadAsStringAsync().Result;

            string msg = string.Format("请求结束，控制器名称：{0}，方法名：{1}，来源渠道：{2}，单号：{3}，请求时长：{4},返回信息：{5}", controlName, actName, valFilter1, valFilter2, timespend, responseContent);
            log.Info(msg);
        });
    }
}

写入日志用的事log4net,这边暂不做讨论。这个特性主要是继承ActionFilterAttribute并重写了方法OnActionExecuting（在调用操作之前发生）和OnActionExecuted（在调用操作之后发生）

例如我在控制器中放入特性
```
public class TestController : ApiController
{
    [HttpPost]
    [HelpAttribute(RequestFilter1 = "Channel", RequestFilter2 = "Serialid")]
    public string Test([FromBody]BasicRequest req)
    {
        return "hello curry";
    }

}

public class BasicRequest
{
    public ChannelEnum Channel { get; set; }
    public string InputText { get; set; }
}

public enum ChannelEnum
{
    App = 1,
    WX = 2,
    PC = 3,
}
```
请求接口后

查看日志

完成