javascript asp教程第十二课---session对象

Overview:

The Session Object is how you track a single user across many pages. It has four (4) properties, two (2) collections, one (1) method, and two (2) events.

Get Started:

In this series of examples we will create a password system. We will use the Session Object to track whether or not a user is authorized to view certain pages. Below are several scripts for lesson12. Look at them, play with, and then read the explanations that come further down the page.

<%@LANGUAGE="JavaScript"%>

<%

//No ASP Here, just a regular HTML Page

%>

<HTML>

To play along with our password page, put in a user name and a password.<BR>

<BR>The correct user name is <I>guest</I>.<BR>

And the correct password is also <I>guest</I>.<BR>

<FORM METHOD="post" ACTION="script12a.asp">

User:<INPUT TYPE="text" SIZE="9" NAME="userName" VALUE="guest"><BR>

Pass:<INPUT TYPE="password" SIZE="9" NAME="userPassword" VALUE="guest">

<BR>

<INPUT TYPE="submit" value="Login">

</FORM>

</HTML>

Click Here to run script12.asp in a new window. Below is script12a.asp.

<%@LANGUAGE="JavaScript"%>

<%

var userName=new String(Request.Form("userName"))

var userPassword=new String(Request.Form("userPassword"))

if (userName=="guest" && userPassword=="guest")

	{

	Session("Authorized")=true

	Response.Redirect("script12b.asp")

	}

else

	{

	Session("Authorized")=false

%>

<HTML>

You did not supply the correct Name & Password.<BR>

<A HREF="script12.asp">Click here</A> to log in.

</HTML>

<%

	} //end else statement

%>

We'll skip over script12b.asp entirely because it's almost exactly the same as script12c.asp. Down below is script12c.asp.

<%@LANGUAGE="JavaScript"%>

<%

if (Session("Authorized")!=true)

	{

%>

<HTML>

You are not an authorized user.<BR>

<A HREF="script12.asp">Click here</A> to log in.

</HTML>

<%

	}

else

	{

%>

<HTML>

The <B>second</B> of two pages that are password protected.<BR>

<A HREF="script12d.asp">Click Here</A> to log out.

</HTML>

<%

	} //end of else statement

%>

Above is script12c.asp, which is the second of two password-protected pages. Below is script12.asp, which is the logout page.

<%@LANGUAGE="JavaScript"%>

<%

if (Session("Authorized")!=true)

	{

%>

<HTML>

You are not an authorized user.<BR>

<A HREF="script12.asp">Click here</A> to log in.

</HTML>

<%

	}

else

	{

	var SessionID=Session.SessionID

	Session.Abandon()

%>

<HTML>

You have sucessfully logged out.<BR>

This was session <%=SessionID%>.<BR><BR>

Now try a link to one of the

pages you've already visited.<BR><BR>

<A HREF="script12b.asp">script12b.asp</A><BR>

<A HREF="script12c.asp">script12c.asp</A><BR>

<A HREF="script12d.asp">script12d.asp</A><BR>

</HTML>

<%

	} //end of else statement

%>

A Quick Explanation:

After all that, the last thing you want to see is another grey box full of code. Sorry to do it one more time but, the keystone to this system is in script12a.asp. I've reprinted it down below.

if (userName=="guest" && userPassword=="guest")

	{

	Session("Authorized")=true

	Response.Redirect("script12b.asp")

	}

Any page can now be turned into a password protected page with the following line: if (Session("Authorized")!=true). Session Variables are part of the Session Collections. Let's talk about them.

Session Collections:

The two Session Collections are Session.Contents and Session.StaticObjects. They parallel the Application.Contents and Application.StaticObjects.

Using Session.Contents("someVariable")="someValue" we can set Session Variables. These variables allow us to carry values from one page to the next. Since Contents is the default collection we can use a little shortcut. It goes like this: Session("someVariable")="someValue".

The shortcut is what you saw in the scripts above.

Session.Contents has two methods of its own. They are Session.Contents.Remove("variableName") and Session.Contents.RemoveAll().

We did not demonstrate StaticObjects in the scripts above. It comes in the form of the <OBJECT> flag (set for Session scope).

No Sharing:

Remember how Application variables could be shared by all viewers on your ASP web site? That's not so with Session Variables. They are private; Session Variables are to be accessed only by one user.

Session.Abandon( ):

My bet is you could figure out Session.Abandon() without any explanation. However, let me just state for the record that Session.Abandon() ends the user's session and releases the Session Variables from memory.

Session Properties:

Let's briefly discuss two properties you are not likely to use. Session.CodePage lets you call for foreign character sets, like Chinese or Russian. Session.LCID is a location identifier. It determines the time zone and language for the server. Don't mess with it.

Now let's move on to something you might actually use from time to time. Session.SessionID is a read-only property generated by the server, and assigned to one specific user during one specific session. The SessionID follows the user from the beginning of the session until the end.

Session.Timeout is the number of minutes that a user can be idle before the Server ends the user's individual session and reclaims the memory that was allocated to Session Variables. (Session.Timeout is demonstrated in the global.asa in lesson 10.)

Session Events:

The two Session events are Session_OnStart() and Session_OnEnd(). These events are accessed in the global.asa. You can see an example of global.asa in lesson 10.

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