.NET Core开发日志——Middleware

发布日期:2019-03-09

熟悉ASP.NET架构的开发者一定对于HTTP Modules与HTTP Handlers不陌生。两者的作用主要是对网络请求执行特定的处理工作。而在.NET Core中,它们都被Middleware(中件间)取代了。

之前的Http Modules和HTTP Handlers是如下图般处理请求的:

现在变成了这样:

一言概括之,Middleware完成了HTTP Modules与HTTP Handlers的原有工作,但又不是简单的化二为一的减法作用。

Middleware减去的其实是与原来ASP.NET中重要的基础——应用程序生命周期事件(application life cycle event)的绑定。

HTTP Modules在初始化时就需要针对HttpApplication的事件作绑定处理,这样当HttpApplication的各项事件被触发时,已绑定的相应处理程序才会按照预期的那样被执行。

public class HelloWorldModule : IHttpModule{ public HelloWorldModule() { } public String ModuleName { get { return "HelloWorldModule" } } // In the Init function register for HttpApplication // events by adding your handlers. public void Init(HttpApplication application) { application.BeginRequest += (new EventHandler(this.Application_BeginRequest)) application.EndRequest += (new EventHandler(this.Application_EndRequest)) } private void Application_BeginRequest(Object source EventArgs e) { // Create HttpApplication and HttpContext objects to access // request and response properties. HttpApplication application = (HttpApplication)source HttpContext context = application.Context context.Response.Write("<h1><font color=red> HelloWorldModule: Beginning of Request </font></h1><hr>") } private void Application_EndRequest(Object source EventArgs e) { HttpApplication application = (HttpApplication)source HttpContext context = application.Context context.Response.Write("<hr><h1><font color=red> HelloWorldModule: End of Request</font></h1>") } public void Dispose() { }}

然后你还需要在web.config配置文件注册这个HTTP Module。

<configuration> <system.web> <httpModules> <add name="HelloWorldModule" type="HelloWorldModule"/> </httpModules> </system.web></configuration>

如果是用Middleware的话,事情就变得很简单了。抛弃IHttpModule接口及HttpModule实现类,不用再关心HttpApplication的任何事件,还有烦人的web.config配置。直接在代码中以最简洁的方式完成工作。

public void Configure(IApplicationBuilder app IHostingEnvironment env){ app.Use(async(context next) =>{ await context.Response.WriteAsync("Beginning of Request") await next.Invoke() await context.Response.WriteAsync("End of Request") }) app.Run(async (context) => { await context.Response.WriteAsync("Hello World!") })}

相似的,对于HTTP Handlers,虽然不用取消对HttpApplication事件的依赖,但以两者的代码实现方式作比较,Middleware亳无疑问胜出一筹。

public class HelloWorldHandler : IHttpHandler{ public HelloWorldHandler() { } public void ProcessRequest(HttpContext context) { HttpRequest Request = context.Request HttpResponse Response = context.Response // This handler is called whenever a file ending // in .sample is requested. A file with that extension // does not need to exist. Response.Write("<html>") Response.Write("<body>") Response.Write("<h1>Hello from a synchronous custom HTTP handler.</h1>") Response.Write("</body>") Response.Write("</html>") } public bool IsReusable { // To enable pooling return true here. // This keeps the handler in memory. get { return false } }}

仍需要在web.config文件中注册HTTP handler。

<configuration> <system.web> <httpHandlers> <add verb="*" path="*.sample" type="HelloWorldHandler"/> </httpHandlers> </system.web></configuration>

换作Middleware的写法:

private static void HandleSample(IApplicationBuilder app){ app.Run(async context => { await context.Response.WriteAsync("Hello Sample") })}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.public void Configure(IApplicationBuilder app IHostingEnvironment env){ app.MapWhen(context => context.Request.Path.Value.EndsWith("sample") HandleSample)}

总结下使用Middleware的优点:

没有对HttpApplication的依赖没有对IHttpModule与IHttpHandler接口的依赖无需在web.config文件中添加各种配置代码简洁

最后需要补充Middleware与HTTP Modules的一点差异。各Middleware中处理请求与响应的顺序是刚好相反的,越早处理请求的Middleware越晚处理响应。而HTTP Modules中处理请求与响应的顺序则保持一致,因为每个HTTP Module请求与响应事件的绑定都是在同一阶段完成的。