.net core mvc route的注册，激活，调用流程
mvc的入口是route，当前请求的url匹配到合适的route之后，mvc根据route所指定的controller和action激活controller并调用action完成mvc的处理流程。下面我们看看服务器是如何调用route的。
core mvc startup基本代码。重点在AddMvc和UseMvc
public class Startup
{
public IConfigurationRoot Configuration { get; }
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
app.UseStaticFiles();
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
});
}
}AddMvc：把各种service加入IOC容器。比如格式化提供程序，action定位器，controllerFactory，controller激活器等等，一应服务全部在这里加入。
UseMvc：最重要的一行代码：builder.UseMiddleware(router); 看到这行代码就清楚的知道route 这个handler 在这里加入到请求委托链拉
public static IMvcBuilder AddMvc(this IServiceCollection services)
{
var builder = services.AddMvcCore();
builder.AddJsonFormatters();
builder.AddCors();
return new MvcBuilder(builder.Services, builder.PartManager);
}
public static IMvcCoreBuilder AddMvcCore(this IServiceCollection services, Action<MvcOptions> setupAction)
{
var builder = services.AddMvcCore();
services.Configure(setupAction);
return builder;
}
internal static void AddMvcCoreServices(IServiceCollection services)
{
services.TryAddSingleton<IActionSelector, ActionSelector>();
services.TryAddSingleton<ActionConstraintCache>();
services.TryAddSingleton<IActionSelectorDecisionTreeProvider, ActionSelectorDecisionTreeProvider>();
// This has a cache, so it needs to be a singleton
services.TryAddSingleton<IControllerFactory, DefaultControllerFactory>();
// Will be cached by the DefaultControllerFactory
services.TryAddTransient<IControllerActivator, DefaultControllerActivator>();
services.TryAddEnumerable(ServiceDescriptor.Transient<IControllerPropertyActivator, DefaultControllerPropertyActivator>());
// Route Handlers
services.TryAddSingleton<MvcRouteHandler>(); // Only one per app
services.TryAddTransient<MvcAttributeRouteHandler>(); // Many per app
}
public static IApplicationBuilder UseMvc(this IApplicationBuilder app, Action<IRouteBuilder> configureRoutes)
{
var routes = new RouteBuilder(app)
{
DefaultHandler = app.ApplicationServices.GetRequiredService<MvcRouteHandler>(),
};
configureRoutes(routes);
routes.Routes.Insert(0, AttributeRouting.CreateAttributeMegaRoute(app.ApplicationServices));
return app.UseRouter(routes.Build());
}
public static IApplicationBuilder UseRouter(this IApplicationBuilder builder, IRouter router)
{
return builder.UseMiddleware<RouterMiddleware>(router);
}如此，mvc的入口route handler就加入了我们的请求委托链中。后续服务器接收到的请求就能交由route匹配，查找action，激活action处理。
router middleware的激活调用
//middleware加入_components请求处理委托链
public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)
{
_components.Add(middleware);
return this;
}
public static class UseMiddlewareExtensions
{
private const string InvokeMethodName = "Invoke";
private static readonly MethodInfo GetServiceInfo = typeof(UseMiddlewareExtensions).GetMethod(nameof(GetService), BindingFlags.NonPublic | BindingFlags.Static);
//注册middleware
public static IApplicationBuilder UseMiddleware(this IApplicationBuilder app, Type middleware, params object[] args)
{
var applicationServices = app.ApplicationServices;
//将middleware 加入请求处理委托链
return app.Use(next =>
{
//解析方法和参数。查找类的Invoke方法作为入口方法。所以middleware只要是个class就行。只要有一个功公共的Invoke方法即可。
var methods = middleware.GetMethods(BindingFlags.Instance | BindingFlags.Public);
var invokeMethods = methods.Where(m => string.Equals(m.Name, InvokeMethodName, StringComparison.Ordinal)).ToArray();
var methodinfo = invokeMethods[0];
var parameters = methodinfo.GetParameters();
var ctorArgs = new object[args.Length + 1];
ctorArgs[0] = next;
Array.Copy(args, 0, ctorArgs, 1, args.Length);
//创建middleware的实例。并且通过构造函数注入相关的service
var instance = ActivatorUtilities.CreateInstance(app.ApplicationServices, middleware, ctorArgs);
//如果方法只有一个参数，默认它就是httpcontext。
if (parameters.Length == 1)
{
return (RequestDelegate)methodinfo.CreateDelegate(typeof(RequestDelegate), instance);
}
//多余一个参数的则构建一个func。并从ioc容器解析参数注入
var factory = Compile<object>(methodinfo, parameters);
return context =>
{
var serviceProvider = context.RequestServices ?? applicationServices;
return factory(instance, context, serviceProvider);
};
});
}
//代码中的创建实例注入service，创建有多个参数的invoke方法注入service具体代码就不贴上来了，占地方。
//构造函数就是匹配最适合的构造函数，然后从IServiceProvider get实例，注入。
//多个参数的invoke就更简单了。直接从IServiceProvider get实例注入。上述源代码git地址，aspnet/HttpAbstractions项目
route handler middleware代码
public class RouterMiddleware
{
private readonly ILogger _logger;
private readonly RequestDelegate _next;
private readonly IRouter _router;
//创建middleware的实例。并且通过构造函数注入相关的service
public RouterMiddleware(RequestDelegate next, ILoggerFactory loggerFactory, IRouter router)
{
_next = next;
_router = router;
_logger = loggerFactory.CreateLogger<RouterMiddleware>();
}
//被调用的方法。从这里开始进入mvc route。
public async Task Invoke(HttpContext httpContext)
{
//此处的 IRouter router对象。是我们在Startup中routes.MapRoute...配置的route集合对象：RouteCollection。当然也还有比如attributeroute等等好几种route。
var context = new RouteContext(httpContext);
context.RouteData.Routers.Add(_router);
await _router.RouteAsync(context);
if (context.Handler == null)
{
//没有匹配到route的情况
_logger.RequestDidNotMatchRoutes();
await _next.Invoke(httpContext);
}
else
{
httpContext.Features[typeof(IRoutingFeature)] = new RoutingFeature()
{
RouteData = context.RouteData,
};
//匹配到路由处理
await context.Handler(context.HttpContext);
}
}
}
//Microsoft.AspNetCore.Routing.RouteCollection
public async virtual Task RouteAsync(RouteContext context)
{
// Perf: We want to avoid allocating a new RouteData for each route we need to process.
// We can do this by snapshotting the state at the beginning and then restoring it
// for each router we execute.
var snapshot = context.RouteData.PushState(null, values: null, dataTokens: null);
for (var i = 0; i < Count; i++)
{
var route = this[i];
context.RouteData.Routers.Add(route);
try
{
//循环所有routes规则，逐一匹配，匹配到一个自然就break。
await route.RouteAsync(context);
if (context.Handler != null)
break;
}
finally
{
if (context.Handler == null)
snapshot.Restore();
}
}
}UseMvc中有一行非常重要的代码。给RouteBuilder的DefaultHandler赋值一个handler。记住这行代码，我们继续往下看。
public static IApplicationBuilder UseMvc(this IApplicationBuilder app, Action<IRouteBuilder> configureRoutes)
{
var routes = new RouteBuilder(app)
{
DefaultHandler = app.ApplicationServices.GetRequiredService<MvcRouteHandler>(),
};
}
//我们在Startup中routes.MapRoute的所有调用最终调用方法都是这个。new Route( routeBuilder.DefaultHandler，....)
//全部都指定了_target为routeBuilder.DefaultHandler
public static IRouteBuilder MapRoute(this IRouteBuilder routeBuilder, string name, string template, object defaults, object constraints, object dataTokens)
{
if (routeBuilder.DefaultHandler == null)
throw new RouteCreationException(Resources.FormatDefaultHandler_MustBeSet(nameof(IRouteBuilder)));
var inlineConstraintResolver = routeBuilder.ServiceProvider.GetRequiredService<IInlineConstraintResolver>();
routeBuilder.Routes.Add(new Route(
routeBuilder.DefaultHandler,
name, template, new RouteValueDictionary(defaults), new RouteValueDictionary(constraints), new RouteValueDictionary(dataTokens), inlineConstraintResolver));
return routeBuilder;
}到这里，我们的逻辑有点绕了，让我们理理清楚：
1.请求进到RouterMiddleware.Invoke()方法
2.调用RouteCollection.RouteAsync()方法，RouteCollection.RouteAsync方法中循环注册的每一个route对象。
并调用route对象的RouteAsync()方法(route对象的RouteAsync方法在它的父类中Microsoft.AspNetCore.Routing.RouteBase)。
这里说的route对象即时Startup中routes.MapRoute生成的route对象（Microsoft.AspNetCore.Routing.Route）。Route继承RouteBase，RouteBase实现IRouter接口
3.RouteBase.RouteAsync()判断当前请求是否符合当前route规则，如果匹配的话，则调用抽象方法OnRouteMatched
4.RouteBase的抽象方法OnRouteMatched，又回到Route对象的OnRouteMatched方法中。调用_target.RouteAsync();_target对象即上面代码中的routeBuilder.DefaultHandler。
5.来到Microsoft.AspNetCore.Mvc.Internal.MvcRouteHandler.RouteAsync()方法中。最重要的一行代码： context.Handler =....
6.调用堆栈最终返回到1中(RouterMiddleware.Invoke())。判断context.Handler == null。为null没找到route匹配的action。不为null则await context.Handler(context.HttpContext)
7.context.Handler即为5中赋值的func。即下面的代码，定位action，调用action。
//Microsoft.AspNetCore.Mvc.Internal.MvcRouteHandler.RouteAsync
public Task RouteAsync(RouteContext context)
{
var candidates = _actionSelector.SelectCandidates(context);
if (candidates == null || candidates.Count == 0)
{
_logger.NoActionsMatched();
return TaskCache.CompletedTask;
}
var actionDescriptor = _actionSelector.SelectBestCandidate(context, candidates);
if (actionDescriptor == null)
{
_logger.NoActionsMatched();
return TaskCache.CompletedTask;
}
context.Handler = (c) =>
{
var routeData = c.GetRouteData();
var actionContext = new ActionContext(context.HttpContext, routeData, actionDescriptor);
if (_actionContextAccessor != null)
_actionContextAccessor.ActionContext = actionContext;
var invoker = _actionInvokerFactory.CreateInvoker(actionContext);
if (invoker == null)
throw new InvalidOperationException( Resources.FormatActionInvokerFactory_CouldNotCreateInvoker(actionDescriptor.DisplayName));
return invoker.InvokeAsync();
};
return TaskCache.CompletedTask;
}至此，route的处理流程大约交代清楚了。包括route的注册，route的激活，route的选择等。
