.NET Core开发日志——Filter
ASP.NET Core MVC中的Filter作用是在请求处理管道的某些阶段之前或之后可以运行特定的代码。
Filter特性在之前的ASP.NET MVC中已经出现,但过去只有Authorization,Exception,Action,Result四种类型,现在又增加了一种Resource类型。所以共计五种。
Resource类型Filter在Authorization类型Filter之后执行,但又在其它类型的Filter之前。且执行顺序也在Model Binding之前,所以可以对Model Binding产生影响。
ASP.NET Core MVC框架中可以看到有ConsumesAttribute及FormatFilter两种实现IResourceFilter接口的类。
ConsumesAttribute会按请求中的Content-Type(内容类型)进行过滤,而FormatFilter能对路由或路径中设置了format值的请求作过滤。
一旦不符合要求,就对ResourceExecutingContext的Result属性设置,这样可以达到短路效果,阻止进行下面的处理。
ConsumesAttribute类的例子:
public void OnResourceExecuting(ResourceExecutingContext context)
{
...
// Only execute if the current filter is the one which is closest to the action.
// Ignore all other filters. This is to ensure we have a overriding behavior.
if (IsApplicable(context.ActionDescriptor))
{
var requestContentType = context.HttpContext.Request.ContentType;
// Confirm the request's content type is more specific than a media type this action supports e.g. OK
// if client sent "text/plain" data and this action supports "text/*".
if (requestContentType != null && !IsSubsetOfAnyContentType(requestContentType))
{
context.Result = new UnsupportedMediaTypeResult();
}
}
}
Filter在ASP.NET Core MVC里除了保留原有的包含同步方法的接口,现在又增加了包含异步方法的接口。
同步
- IActionFilter
- IAuthorizationFilter
- IExceptionFilter
- IResourceFilter
- IResultFilter
异步
- IAsyncActionFilter
- IAsyncAuthorizationFilter
- IAsyncExceptionFilter
- IAsyncResourceFilter
- IAsyncResultFilter
新的接口不像旧有的接口包含两个同步方法,它们只有一个异步方法。但可以实现同样的功能。
public class SampleAsyncActionFilter : IAsyncActionFilter
{
public async Task OnActionExecutionAsync(
ActionExecutingContext context,
ActionExecutionDelegate next)
{
// 在方法处理前执行一些操作
var resultContext = await next();
// 在方法处理后再执行一些操作。
}
}
Attribute形式的Filter,其构造方法里只能传入一些基本类型的值,例如字符串:
public class AddHeaderAttribute : ResultFilterAttribute
{
private readonly string _name;
private readonly string _value;
public AddHeaderAttribute(string name, string value)
{
_name = name;
_value = value;
}
public override void OnResultExecuting(ResultExecutingContext context)
{
context.HttpContext.Response.Headers.Add(
_name, new string[] { _value });
base.OnResultExecuting(context);
}
}
[AddHeader("Author", "Steve Smith @ardalis")]
public class SampleController : Controller
如果想要在其构造方法里引入其它类型的依赖,现在可以使用ServiceFilterAttribute,TypeFilterAttribute或者IFilterFactory方式。
ServiceFilterAttribute需要在DI容器中注册:
public class GreetingServiceFilter : IActionFilter
{
private readonly IGreetingService greetingService;
public GreetingServiceFilter(IGreetingService greetingService)
{
this.greetingService = greetingService;
}
public void OnActionExecuting(ActionExecutingContext context)
{
context.ActionArguments["param"] =
this.greetingService.Greet("James Bond");
}
public void OnActionExecuted(ActionExecutedContext context)
{ }
}
services.AddScoped<GreetingServiceFilter>();
[ServiceFilter(typeof(GreetingServiceFilter))]
public IActionResult GreetService(string param)
TypeFilterAttribute则没有必要:
public class GreetingTypeFilter : IActionFilter
{
private readonly IGreetingService greetingService;
public GreetingTypeFilter(IGreetingService greetingService)
{
this.greetingService = greetingService;
}
public void OnActionExecuting(ActionExecutingContext context)
{
context.ActionArguments["param"] = this.greetingService.Greet("Dr. No");
}
public void OnActionExecuted(ActionExecutedContext context)
{ }
}
[TypeFilter(typeof(GreetingTypeFilter))]
public IActionResult GreetType1(string param)
IFilterFactory也是不需要的:
public class GreetingFilterFactoryAttribute : Attribute, IFilterFactory
{
public bool IsReusable => false;
public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)
{
var logger = (IGreetingService)serviceProvider.GetService(typeof(IGreetingService));
return new GreetingFilter(logger);
}
private class GreetingFilter : IActionFilter
{
private IGreetingService _greetingService;
public GreetingFilter(IGreetingService greetingService)
{
_greetingService = greetingService;
}
public void OnActionExecuted(ActionExecutedContext context)
{
}
public void OnActionExecuting(ActionExecutingContext context)
{
context.ActionArguments["param"] = _greetingService.Greet("Dr. No");
}
}
}
[GreetingFilterFactory]
public IActionResult GreetType1(string param)
Filter有三种范围:
- Global
- Controller
- Action
后两种可以通过Attribute的方式附加到特定Action方法或者Controller类之上。对于Global,则要在ConfigureServices方法内部添加。
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc(options =>
{
// by instance
options.Filters.Add(new AddDeveloperResultFilter("Tahir Naushad"));
// by type
options.Filters.Add(typeof(GreetDeveloperResultFilter));
});
}
顾名思义,Global将对所有Controller及Action产生影响。所以务必对其小心使用。
这三种范围的执行顺序在设计程序的时候也需要多作考虑:
- Global范围的前置处理代码
- Controller范围的前置处理代码
- Action范围的前置处理代码
- Action范围的后置处理代码
- Controller范围的后置处理代码
- Global范围的后置处理代码
典型的前置处理代码如常见的OnActionExecuting方法,而常见的后置处理代码,则是像OnActionExecuted方法这般的。