使用ASP.NET Global.asax 文件

使用这些事件的一个关键问题是知道它们被触发的顺序。application_init 和application_start 事件在应用程序第一次启动时被触发一次。相似地，application_disposed 和 application_end 事件在应用程序终止时被触发一次。此外，基于会话的事件（session_start 和 session_end）只在用户进入和离开站点时被使用。其余的事件则处理应用程序请求，这些事件被触发的顺序是：

·         application_beginrequest

·         application_authenticaterequest

·         application_authorizerequest

·         application_resolverequestcache

·         application_acquirerequeststate

·         application_prerequesthandlerexecute

·         application_presendrequestheaders

·         application_presendrequestcontent

·         <<执行代码>>

·         application_postrequesthandlerexecute

·         application_releaserequeststate

·         application_updaterequestcache

·         application_endrequest

这些事件常被用于安全性方面。下面这个 c# 的例子演示了不同的global.asax 事件，该例使用application_authenticate 事件来完成通过 cookie 的基于表单（form）的身份验证。此外，application_start 事件填充一个应用程序变量，而session_start 填充一个会话变量。application_error 事件显示一个简单的消息用以说明发生的错误。

protected void application_start(object sender, eventargs e) {
application["title"] = "builder.com sample";
}
protected void session_start(object sender, eventargs e) {
session["startvalue"] = 0;
}
protected void application_authenticaterequest(object sender, eventargs e) {
// extract the forms authentication cookie
string cookiename = formsauthentication.formscookiename;
httpcookie authcookie = context.request.cookies[cookiename];
if(null == authcookie) {
// there is no authentication cookie.
return;
}
formsauthenticationticket authticket = null;
try {
authticket = formsauthentication.decrypt(authcookie.value);
} catch(exception ex) {
// log exception details (omitted for simplicity)
return;
}
if (null == authticket) {
// cookie failed to decrypt.
return;
}
// when the ticket was created, the userdata property was assigned
// a pipe delimited string of role names.
string[2] roles
roles[0] = "one"
roles[1] = "two"
// create an identity object
formsidentity id = new formsidentity( authticket );
// this principal will flow throughout the request.
genericprincipal principal = new genericprincipal(id, roles);
// attach the new principal object to the current httpcontext object
context.user = principal;
}
protected void application_error(object sender, eventargs e) {
response.write("error encountered.");

这个例子只是很简单地使用了一些global.asax 文件中的事件；重要的是要意识到这些事件是与整个应用程序相关的。这样，所有放在其中的方法都会通过应用程序的代码被提供，这就是它的名字为global 的原因。

这里是前面的例子相应的 vb.net 代码：

sub application_start(byval sender as object, byval e as eventargs)
application("title") = "builder.com sample"
end sub
sub session_start(byval sender as object, byval e as eventargs)
session("startvalue") = 0
end sub
sub application_authenticaterequest(byval sender as object, byval e as
 eventargs)
' extract the forms authentication cookie
dim cookiename as string
cookiename = formsauthentication.formscookiename
dim authcookie as httpcookie
authcookie = context.request.cookies(cookiename)
if (authcookie is nothing) then
' there is no authentication cookie.
return
end if
dim authticket as formsauthenticationticket
authticket = nothing
try
authticket = formsauthentication.decrypt(authcookie.value)
catch ex as exception
' log exception details (omitted for simplicity)
return
end try
dim roles(2) as string
roles(0) = "one"
roles(1) = "two"
dim id as formsidentity
id = new formsidentity(authticket)
dim principal as genericprincipal
principal = new genericprincipal(id, roles)
' attach the new principal object to the current httpcontext object
context.user = principal
end sub
sub application_error(byval sender as object, byval e as eventargs)
response.write("error encountered.")
end sub

资源

global.asax 文件是 asp.net 应用程序的中心点。它提供无数的事件来处理不同的应用程序级任务，比如用户身份验证、应用程序启动以及处理用户会话等。你应该熟悉这个可选文件，这样就可以构建出健壮的asp.net 应用程序。