Asp.Net Core Filter in simple terms those things -AOP

I. Introduction

Share ASP.NET Core Filter before use, let's talk about AOPwhat AOP is it?

AOPFull name Aspect Oriented Programmingmeans Oriented Programming, also known as method-oriented programming, is the case of implementing by way of pre-compiled and run-time dynamic way agents do not modify the source code to add functionality to the program dynamically unified technology.

AOP Using a technique known as "cross" technique, a cross-sectional unlock object inside the package, the common behavioral effects encapsulated into a plurality of classes of reusable modules, and name it Aspectsection. The so-called cut surface, regardless of the service is simply, it is a common logic module called service, which facilitates reducing code duplication encapsulated system, reduce the coupling module, use of the future operability and maintainability .

AOP can use to isolate each part of the business logic, business logic, thereby reducing the degree of coupling between the parts, improve the reusability of the program, while improving development efficiency.

AOP usage scenarios include logging, performance statistics, security control, transaction processing, exception handling.

Two, Filter- filter

Filter is a continuation of ASP.NET MVC product, also retained five of Filter, respectively Authorization Filter, Resource Filter, Action Filter , Exception Filter and Result Filter.
Can effectively handle incoming and outgoing packet processing through different Filter, Filter This article deals introduces five kinds of works ASP.NET Core.

2.1 Filter Introduction

ASP.NET Core Filter can use the following five:

• The Filter the Authorization:
  the Authorization is the highest priority in the five Filter, commonly used to verify Request together illegal, it is illegal to skip back.
• Resource Filter: Resource is the second priority, will be executed before the Model Binding after Authorization. Model is usually required for processing before use.
• Exception Filter: Filter exception handling.
• Action Filter: Filter most commonly used, and out of the packet will go through it, no need to pay special attention to the use. With the Resource Filter is very similar, but not through the Model Binding.
• Result Filter: When Action is completed, will eventually pass Filter.
  

Third, the application of the five Filter

This chapter is mainly to explain and implement the use of five filters Asp.Net Core of.

3.1 Authonization Filter

Access control filter
may be achieved by complex the Filter Authonization 权限角色认证, 登陆授权and other operations
achieved examples code as follows:

    public class AuthonizationFilter :Attribute,IAuthorizationFilter
    {
        public void OnAuthorization(AuthorizationFilterContext context)
        {
            //这里可以做复杂的权限控制操作
            if (context.HttpContext.User.Identity.Name != "1") //简单的做一个示范
            {
                //未通过验证则跳转到无权限提示页
                RedirectToActionResult content = new RedirectToActionResult("NoAuth", "Exception", null);
                context.Result = content;
            }
        }
    }

3.2 Resource Filter

Resource filter
may be performed by the Filter the Resource 资源缓存, 防盗链and other operations.
Use Resource Filter abstract interface required to achieve IResourceFilter

   public class ResourceFilter : Attribute,IResourceFilter
    {
        public void OnResourceExecuted(ResourceExecutedContext context)
        {
            // 执行完后的操作
        }

        public void OnResourceExecuting(ResourceExecutingContext context)
        {
            // 执行中的过滤器管道
        }
    }

3.3 Exception Filter

You can globally Execption Filter through a filter 异常日志收集operation.

使用Execption Filter 要求实现IExceptionFilter 抽象接口
IExceptionFilter接口会要求实现OnException方法，当系统发生未捕获异常时就会触发这个方法。OnException方法有一个ExceptionContext异常上下文，其中包含了具体的异常信息，HttpContext及mvc路由信息。系统一旦出现未捕获异常后，比较常见的做法就是使用日志工具，将异常的详细信息记录下来，方便修正调试。下面是日志记录的实现。　　

  public class ExecptionFilter : Attribute, IExceptionFilter
  {
        private ILogger<ExecptionFilter> _logger;
        //构造注入日志组件
        public ExecptionFilter(ILogger<ExecptionFilter> logger)
        {
            _logger = logger;
        }

        public void OnException(ExceptionContext context)
        {
            //日志收集
            _logger.LogError(context.Exception, context?.Exception?.Message??"异常");
        }
    }

3.4 Action Filter

作用：可以通过ActionFilter 拦截 每个执行的方法进行一系列的操作，比如：执行操作日志、参数验证，权限控制 等一系列操作。

使用Action Filter 需要实现IActionFilter 抽象接口，IActionFilter 接口要求实现OnActionExecuted 和OnActionExecuting 方法

    public class ActionFilter : Attribute, IActionFilter
    {
        public void OnActionExecuted(ActionExecutedContext context)
        {
            //执行完成....
        }

        public void OnActionExecuting(ActionExecutingContext context)
        {
            //执行中...
        }
    }

3.5 Result Filter

结果过滤器，可以对结果进行格式化、大小写转换等一系列操作。

使用Result Filter 需要实现IResultFilter 抽象接口，接口要求实现
OnResultExecuting 方法 和OnResultExecuted 方法

• OnResultExecuting ：Called before the action result executes. 在操作结果执行之前调用
• OnResultExecuted ：Called after the action result executes. 在操作结果执行之后调用

具体代码实现代码如下：

public class ResultFilter : Attribute, IResultFilter
 {
        public void OnResultExecuted(ResultExecutedContext context)
        { 
            // 在结果执行之后调用的操作...
        }

        public void OnResultExecuting(ResultExecutingContext context)
        {
            // 在结果执行之前调用的一系列操作
        }
    }

四、Asp.Net Core 过滤器的注册方式

这一篇章主要来分析探讨Asp.Net Core 中过滤器的三种注册方式Action、Controller、全局 。

4.1 Action 注册方式

Action 注册方式是局部注册方式，针对控制器中的某个方法上标注特性的方式进行注册，代码如下：

 [AuthonizationFilter()]
 public IActionResult Index()
 {
            return View();
 }

4.2 Controller 注册方式

了解过Action 特性注册方式的同学，一定发现了它的不好之处就是我一个控制器里面需要使用同一套Filter 的时候，需要一个一个Action 标注特性注册，是不是很繁琐呢？有没有其他方式进行代替这些繁琐的操作呢？微软给我们提供了简便的控制器标注注册方式，代码如下：

 [AuthonizationFilter()]
 public class FirstController : Controller
  {
        private ILogger<FirstController> _logger;

        public FirstController(ILogger<FirstController> logger)
        {
            _logger = logger;
        }

        public IActionResult Index()
        {
            return View();
        }
 }

4.3 全局注册方式

现在有些同学考虑了一些全局的情况，比如我要全局处理系统中的异常，或者收集操作日志等，需要全局注册一个ExceptionFilter 来实现，就不需要每一个Controller 中进行代码注册，方便快捷。代码如下：

 public void ConfigureServices(IServiceCollection services)
  {
            //全局注册异常过滤器
            services.AddControllersWithViews(option=> {
                option.Filters.Add<ExecptionFilter>();
            });

            services.AddSingleton<ISingletonService, SingletonService>();
}

4.4 TypeFilter 和 ServiceFilter 注册方式

上面的五大过滤器中事例代码中其中有一个过滤器的代码比较特，再来回顾ExceptionFilter过滤器的实现代码：

    public class ExecptionFilter : Attribute, IExceptionFilter
    {
        private ILogger<ExecptionFilter> _logger;
        //构造注入日志组件
        public ExecptionFilter(ILogger<ExecptionFilter> logger)
        {
            _logger = logger;
        }

        public void OnException(ExceptionContext context)
        {
            //日志收集
            _logger.LogError(context.Exception, context?.Exception?.Message??"异常");
        }
    }

从上面的代码中可以发现 ExceptionFilter 过滤器实现中存在日志服务的构造函数的注入，也就是说该过滤器依赖于其他的日志服务，但是日志服务都是通过DI 注入进来的；再来回顾下上面Action 注册方式或者Controller 注册方式 也即Attribute 特性标注注册方式，本身基础的特性是不支持构造函数的，是在运行时注册进来的，那要解决这种本身需要对服务依赖的过滤器需要使用 TypeFilter 或者ServiceFilter 方式进行过滤器的标注注册。

TypeFilter 和ServiceFilter 的区别。

• ServiceFilter和TypeFilter都实现了IFilterFactory
• ServiceFilter需要对自定义的Filter进行注册，TypeFilter不需要
• ServiceFilter的Filter生命周期源自于您如何注册，而TypeFilter每次都会创建一个新的实例

TypeFilter 使用方式

代码如下：

[TypeFilter(typeof(ExecptionFilter))]
public IActionFilter Index2()
{
      return View();
}

通过上面的代码可以发现AuthonizationFilter 是默认的构造器，但是如果过滤器中构造函数中存在参数，需要注入服务那该怎么办呢?，比如上面的ExceptionFilter 代码，就不能使用这种方式进行注册，需要使用服务特性的方式，我们可以选择使用 代码如下：

[TypeFilter(typeof(ExecptionFilter))]
public IActionFilter Index2()
{
           return View();
}

ServiceFilter 使用方式

控制器中的代码如下：

[ServiceFilter(typeof(ExecptionFilter))]
public IActionFilter Index2()
{
           return View();
}

注册服务的代码如下：

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
       Console.WriteLine("ConfigureServices");
       services.AddControllersWithViews();

       //services.AddControllersWithViews(option=> {
       //    option.Filters.Add<ExecptionFilter>();
       //});
        
        //注册过滤器服务，使用ServiceFilter 方式必须要注册 否则会报没有注册该服务的相关异常
        services.AddSingleton<ExecptionFilter>();
}

如果您觉的不错，请微信扫码关注 【dotNET 博士】公众号，后续给您带来更精彩的分享