Asp.net Mvc是当前使用比较多的web框架，也是比较先进的框架。我打算根据自己的实际项目经验以及相关的源码和一些使用Asp.net Mvc的优秀项目（主要是orchard）来说一说自己对于Asp.net Mvc原理的理解和一些实践经验。目前.net的大部分源码都已经开放，这大大方便了我们对Asp.net Mvc的分析，下面就从Http请求进入Mvc框架处理之前的基本流程说起。
由于各IIS版本和工作模式（经典模式、集成模式）的不同，Http请求进入Asp.net的处理通道并不一样，这里不去细究里面的细节，就从创建应用程序域开始：
AppManagerAppDomainFactory分析
注：AppDomainFactory及AppManagerAppDomainFactory类在System.Web.Hosting中实现
在创建Appdomain时会调用IAppDomainFactory接口，该接口的实现如下:
public sealed class AppDomainFactory : IAppDomainFactory {
private AppManagerAppDomainFactory _realFactory;
public AppDomainFactory() {
_realFactory = new AppManagerAppDomainFactory();
}
public Object Create(String module, String typeName, String appId, String appPath,String strUrlOfAppOrigin, int iZone) {
return _realFactory.Create(appId, appPath);
}
}
该实现会调用AppManagerAppDomainFactory完成实际的创建过程。
public sealed class AppManagerAppDomainFactory : IAppManagerAppDomainFactory {
private ApplicationManager _appManager;
public AppManagerAppDomainFactory() {
_appManager = ApplicationManager.GetApplicationManager();
_appManager.Open();
}
public Object Create(String appId, String appPath) {
try {
if (appPath[0] == ‘.‘) {
System.IO.FileInfo file = new System.IO.FileInfo(appPath);
appPath = file.FullName;
}
if (!StringUtil.StringEndsWith(appPath, ‘\\‘)) {
appPath = appPath + "\\";
}
ISAPIRuntime isapiRuntime = (ISAPIRuntime)_appManager.CreateObjectInternal(appId, typeof(ISAPIRuntime), appHost,false, null);
isapiRuntime.StartProcessing();
return new ObjectHandle(isapiRuntime);
}
catch (Exception e) {
Debug.Trace("internal", "AppDomainFactory::Create failed with " + e.GetType().FullName + ": " + e.Message + "\r\n" + e.StackTrace);
throw;
}
}
}
代码的主要作用，就是通过ApplicationManager的CreateObjectInternal创建AppDomain，创建HostingEnvironment等，最终获取ISAPIRuntime的实例，然后让非托管代码调用。
ApplicationManager分析
注：ApplicationManager类在System.Web.Hosting中实现
首先看ApplicationManager类中的静态的创建ApplicationManager对象的方法：
public static ApplicationManager GetApplicationManager() {
if (_theAppManager == null) {
lock (_applicationManagerStaticLock) {
if (_theAppManager == null) {
if (HostingEnvironment.IsHosted)
_theAppManager = HostingEnvironment.GetApplicationManager();
if (_theAppManager == null)
_theAppManager = new ApplicationManager();
}
}
}
return _theAppManager;
}
如果HostingEnvironment已经创建则可以直接返回当前HostingEnvironment设置的ApplicationManager，如果没有则创建新的ApplicationManager实例。
然后看ApplicationManager的CreateObjectInternal方法：
internal IRegisteredObject CreateObjectInternal(String appId, Type type, IApplicationHost appHost, bool failIfExists, HostingEnvironmentParameters hostingParameters) {
if (!typeof(IRegisteredObject).IsAssignableFrom(type))
throw new ArgumentException(SR.GetString(SR.Not_IRegisteredObject, type.FullName), "type");
HostingEnvironment env = GetAppDomainWithHostingEnvironment(appId, appHost, hostingParameters);
ObjectHandle h = env.CreateWellKnownObjectInstance(type.AssemblyQualifiedName, failIfExists);
return (h != null) ? h.Unwrap() as IRegisteredObject : null;
}
首先要先取得HostingEnvironment的实例，然后通过该实例的CreateWellKnownObjectInstance方法返回上述Create方法需要的ISAPIRuntime的实例。先来看如何获取HostingEnvironment实例的方法GetAppDomainWithHostingEnvironment。
private HostingEnvironment GetAppDomainWithHostingEnvironment(String appId, IApplicationHost appHost, HostingEnvironmentParameters hostingParameters) {
LockableAppDomainContext ac = GetLockableAppDomainContext (appId);
lock (ac) {
HostingEnvironment env = ac.HostEnv;
if (env != null) {
try {
env.IsUnloaded();
}
catch(AppDomainUnloadedException) {
env = null;
}
}
if (env == null) {
env = CreateAppDomainWithHostingEnvironmentAndReportErrors(appId, appHost, hostingParameters);
ac.HostEnv = env;
Interlocked.Increment(ref _accessibleHostingEnvCount);
}
return env;
}
}
首先会检查字典是否会有已经存在的HostingEnvironment实例，如果有就返回，没有就会创建一个新的并保存到字典中，查看相关代码发现最终会调用ApplicationManager的私有方法CreateAppDomainWithHostingEnvironment创建AppDomain和HostingEnvironment。
private HostingEnvironment CreateAppDomainWithHostingEnvironment(String appId, IApplicationHost appHost, HostingEnvironmentParameters hostingParameters)
{
……
appDomain = AppDomain.CreateDomain(domainId,GetDefaultDomainIdentity(),setup);
……
Type hostType = typeof(HostingEnvironment);
String module = hostType.Module.Assembly.FullName;
String typeName = hostType.FullName;
ObjectHandle h = null;
……
try {
h = Activator.CreateInstance(appDomain, module, typeName);
}
……
HostingEnvironment env = (h != null) ? h.Unwrap() as HostingEnvironment : null;
if (env == null)
throw new SystemException(SR.GetString(SR.Cannot_create_HostEnv));
IConfigMapPathFactory configMapPathFactory = appHost.GetConfigMapPathFactory();
if (appDomainStartupConfigurationException == null) {
env.Initialize(this, appHost, configMapPathFactory, hostingParameters, policyLevel);
}
else {
env.Initialize(this, appHost, configMapPathFactory, hostingParameters, policyLevel, appDomainStartupConfigurationException);
}
return env;
}
可以看到代码创建了AppDomain和HostingEnvironment实例，创建HostingEnvironment实例以后，紧接着会调用其Initialize方法来进行初始化，然后返回对象实例。
HostingEnvironment分析
Initialize初始化方法，注意该方法的第一个参数是this，也就是ApplicationManager实例自身，这样会在HostingEnvironment中设置ApplicationManager，因而初始化之后可以通过HostingEnvironment获取ApplicationManager 。Initialize方法调用HttpRuntime的静态方法，进行一些初始化工作（其中会调用BuildManager的InitializeBuildManager方法进行初始化另外一些工作，其中包括编译App_Code目录下所有的.NET源代码）。最后如果HostingEnvironment初始化失败时会设置hostingInitFailed为true。
internal void Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)
{
……
_appManager = appManager;
……
HttpRuntime.InitializeHostingFeatures(hostingFlags,policyLevel,appDomainCreationException);
……
catch (Exception e) {
_hostingInitFailed = true;
}
}
创建HostingEnvironment后，会调用其方法CreateWellKnownObjectInstance创建ISAPIRuntime。创建好ISAPIRuntime实例后初始化工作就完成了第一个阶段，整个过程如下图所示：
