.NET Core开发日志——Middleware
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()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\n"); await next.Invoke(); await context.Response.WriteAsync("End of Request\n"); }); app.Run(async (context) => { await context.Response.WriteAsync("Hello World!\n"); }); }
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。
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