Download Session and State Management

Session and State
Management
1
Company Confidential
Introduction
• ASP.NET, like traditional ASP,
– provides the facility to track a user's session using Session
State. Web applications are built on Hypertext Transfer
Protocol (HTTP).
– HTTP being a stateless protocol, each request to the
server from the client is understood as an independent
request. ASP.NET provides a powerful way to store a
user’s session specific data using the Session State which
is accessible as long as the user’s session is alive
• This module discusses Session State, its advantages and
disadvantages, the Session storage modes and how we can
configure the same using the application’s web.config file
Objectives
• Types of State Management –
– Applilcation State, Session state, Cookie state, View
state
• Application and Session Variables
• Cookies and Cookieless Sessions
• Storing Application and Session Data in different modes
– In-process storage, Session State Service, Microsoft
SQL Server
• Using Session Variables
• Using Cookies
• Using Application Variables
• Using the Cache Object
Objectives (Cont…)
• Using ASP.Net Caching
– Output Caching
– Partial Page Caching
• Using Dynamic Properties
State Management
• ASP.NET provides four types of state:
– Applilcation State
– Session state
– Cookie state
– View state
• ASP.NET, like its predecessor, ASP,
– provides a pair of objects for managing applicationlevel state and session-level state.
• Application state
– is where information that is global to the application
may be stored.
– This state is typically stored once and then read from
many times.
State Management (Cont…)
• Session state
– is maintained on a per-client basis.
– When a client first accesses any page in an application, an
ASP.NET generated session ID is created.
– That session ID is then transmitted between the server
and the client via HTTP either using client-side cookies or
encoded in a mangled version of the URL.
• Cookies
– provide the ability to store small amounts of data on a
client's machine.
– Once a cookie is set, all subsequent pages accessed by
the same client will transmit the cookie and its value.
State Management (Cont…)
• View state is a another way of storing state on behalf of a
client by saving and restoring values from a hidden field when
a form is posted.
• Advantages & Disadvantages of State Type:
Type of
State
Application
Scope of State Advantages
Global to the
application
Disadvantages
•shared across •Overuse limits scalability
all clients
•Not shared across multiple
machines in a Web farm or
processors in a Web garden
•Primary purpose subsumed
by data cache in ASP.NET
State Management (Cont…)
• Advantages & Disadvantages of State Type:
Type of
State
Session
Scope of Advantages Disadvantages
State
Per client •Can configure •Requires cookies or
to be shared URL managing to
across
mange client
machines in a association
Web farm and •Off-host storage can
processors in a be inefficient
Web Garden
State Management (Cont…)
• Advantages & Disadvantages of State Type:
Type of Scope of Advantages
State
State
Cookie Per client •Works
regardless of
server
configuration
•State stored on
client
•State can live
beyond current
session
Disadvantages
•Limited memory (4KB)
•Clients may not
support cookies or may
explicitly disable them
•State is sent back and
forth with each request
State Management (Cont…)
• Advantages & Disadvantages of State Type:
Type of
State
View
Scope of
State
Across
POST
request to
the same
page
Advantages Disadvantages
•Works
•State is retained only
regardless of with POST request
server
made to the same page
configuration •State is sent back and
forth with each request
Application and Session
Variables
• An object is initialized in the Application_Start
event and further access is read-only.
• The Refresh Variable Dialog is used to select the
method for maintaining Session Variables in
ASP.NET application.
• Because an application and all the objects it stores
can be concurrently accessed by different threads, it
is better to store only infrequently modified data with
application scope. Ideally an object is initialized in
the Application_Start event and further access is
read-only.
Application and Session Variables (Cont…)
• As the data is never modified after initialization,
you do not have to make any provisions for
serializing access.
• Net Sessions provides a simple and complete
methodology for creating, using, and maintaining
Session Variables in ASP.NET applications.
• The Refresh Variable Dialog is used to select the
method for maintaining Session Variables in
ASP.NET application.
Application and Session Variables
(Cont…)
• Session state features can be configured via the
<sessionState> section in a web.config file.
• ASP.NET will store the session state in the same
process that processes the request, just as ASP
does.
If cookies are not available, a session can be
tracked by adding a session identifier to the URL.
This can be enabled by setting the following:
<sessionState
cookieless="true"
/>
Application and Session Variables
(Cont…)
• To provide individual data for a user during a
session, data can be stored with session scope.
• ASP.NET can store session data in an external
process, which can even reside on another
machine. To enable this feature:
– Start the ASP.NET state service, either using the
Services snap-in or by executing "net start
aspnet_state" on the command line. The state
service will by default listen on port 42424. To
change the port, modify the registry key for the
service:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentCont
rolSet\Services\aspnet_state\Parameters\Port.
Application and Session Variables
(Cont…)
– Set the mode attribute of the <sessionState>
section to "StateServer".
– Configure the stateConnectionString
attribute with the values of the machine on
which you started aspnet_state.
The http cookie object
• Cookie :
– A cookie is a small file on the user’s computer that
contains information specific to one web site.
– This file can contains things such as username and
passwords that will be used to customize a user’s visit
to the site.
– Cookies can contain any simple data type such as
string, integer, floats, Booleans, and so on.
– For example many sites that display news headlines
will allow users to select which types of news they
want to see . This information can be stored in
cookies so that the next time the user visits, the site
can read those values and customize accordingly.
The http cookie object
• The http cookies object provides methods
for accessing and creating these cookies.
You can use this object to examine the
property of the cookie. However the most
common way to manipulate cookies is
through the request and response object
which both have a cookies properties that
return a reference to an http cookie object.
Cookies and Cookieless Sessions
• A cookie is a piece of text that a Web site can
store on a user's machine to be retrieved and
reused later. The information stored consists of
harmless name-value pairs.
• cookies are not part of the standard HTTP
specification, so they imply a collaboration
between browsers and Web sites to work.
• Not all browsers support cookies and not all
users may have cookie support enabled in their
own copy of the browser.
Cookies and Cookieless Sessions
• Storing cookies on the client is one of the
methods that ASP.NET's session state uses to
associate requests with sessions.
• Cookies can also be used directly to persist
data between requests, but the data is then
stored on the client and sent to the server with
every request.
• Browsers place limits on the size of a cookie;
only a maximum of 4096 bytes to be acceptable.
Cookies and Cookieless Sessions
(Cont…)
• When the data is stored on the client, the
Page_Load method in the file cookies1.aspx
checks whether the client has sent a cookie. If
not, a new cookie is created and initialized and
stored on the client.
• To make a cookie persistent between sessions,
the Expires property on the HttpCookie class
has to be set to a date in the future.
• To enable cookieless sessions in ASP.NET
application, change the following configuration
setting:
<sessionState cookieless="true" />
Cookies and Cookieless Sessions (Cont…)
• If the cookieless attribute of the
<sessionState> section is set to true.
• The module generates a new session ID,
twist the URL by adding the session ID just
before the resource name, and redirects
the browser to the new URL using the
HTTP 302 command.
Storing Application and Session Data
•
•
We have three choices for storing session state in an
ASP.NET application:
– In-process storage
– Session State Service
– Microsoft SQL Server
In-process storage:
– The default location for session state storage is in
the ASP.NET process itself.
– If we don’t change the default configuration of
ASP.NET, then session state information is stored in
memory of ASP.NET process itself. If we restart the
WWW server (or if it crashes for some reason), all of
this information is lost
Storing Application and Session Data
(Cont…)
•
•
Session State Service:
– To use the State Service, we need to edit the
sessionState element in ASP.NET application's
web.config file
<sessionState mode="StateServer"
stateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString= "data source=127.0.0.1;user
id=sa;password=" cookieless="false" timeout="20"
/>
– It need to start the ASP.NET State Service on
the computer that we specified in the
stateConnectionString attribute
Storing Application and Session Data
(Cont…)
•
•
Session State Service (Cont…)
– If we make the changes, it shows slightly
different behavior: session state persists even if
we recycle the ASP.NET process
There are two main advantages to using the State
Service
– First, it is not running in the same process as
ASP.NET, so a crash of ASP.NET will not
destroy session information.
– Second, the stateConnectionString that's used
to locate the State Service includes the TCP/IP
address of the service, which need not be
running on the same computer as ASP.NET.
Storing Application and Session Data
(Cont…)
• Session State Service (Cont…)
–
- This allows you to share state information
across a web garden (multiple processors on
the same computer) or even across a web
farm (multiple servers running the
application).
• With the default in-process storage, we
can't share state information between
multiple instances of application.
Storing Application and Session Data
(Cont…)
Session State Service (Cont…)
• The major disadvantage of using the
State Service
– is that it's an external process, rather than
part of ASP.NET.
– That means that reading and writing session
state is slower than it would be if you kept
the state in-process. (ie), it's one more
process that need to be manage.
Storing Application and Session Data
(Cont…)
Microsoft SQL Server:
– To use SQL Server for storing session state, you need to
perform several setup steps:
– - Run the InstallSqlState.sql script on the Microsoft SQL
Server where you intend to store session state.
– This script will create the necessary database and
database objects.
– The .NET Framework installs this script in the same
folder as its compilers and other tools—
– for example,
C:\WINNT\Microsoft.NET\Framework\v1.0.3705 on a
Windows 2000 computer with the 1.0 version of the
Framework.
Storing Application and Session Data
(Cont…)
•
•
Microsoft SQL Server (Cont…)
– Edit the sessionState element in the web.config file
for your ASP.NET application as follows:
<sessionState mode="SQLServer"
stateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString= "data
source=SERVERHAME;user id=sa;password="
cookieless="false" timeout="20"/>
Supply the server name, user name, and password for
a SQL Server account that has access to the session
state database in the sqlConnectionString attribute.
Storing Application and Session Data
(Cont…)
• Microsoft SQL Server (Cont…)
– Like the State Service, SQL Server lets you
share session state among the processors in
a web garden or the servers in a web farm
– Like the State Service, SQL Server is slower
than keeping session state in process
The session object
• The session object presents a very
interesting concept.
• Because the web is a stateless medium
information about a particular user is hard
to keep track of. There’s no way to use
HTTP to find out if a series of request
comes from one user or a bunch of
different users. This makes it hard to tailor
a web site for one user.
The session object (Cont…)
• The session object combats this limitation.
– It allows you to store items that are pertinent to a specific
user in a single location on the server.
– Essentially it acts as that users personal storage locker of
information.
– Imagine lockers in a school you put your belonging in your
locker to store while you are in class. When you leave for
the day the locker is emptied.
• New term- The session object works by the same mechanism
. When a user visits your site he’s allocated a “locker” into
which the developer can put whatever information she likes.
The user’s time at the site is called a session.
• Once the user leaves the site the locker is abounded the
information is lost and the session ends.
The session object (Cont…)
• Once the user leaves the site the locker is
abounded the information is lost and the session
ends.
• Imagine that user comes to your site and enter
his name in a form which you would like to
remember. You can put the name into the
session object and then recall it from anywhere
you want assuming the session has not ended.
The syntax is as follows:
Session. add (variable name, value)
Or:
Session( variable name)= value;
Controlling session
• There are various ways to control how the
session object behaves in your ASP>NET
applications.
– The first is the time out value , which sets how long a
session can be idle before ASP.NET abandons it.
– In other words if a user visits your site but does not
click on anything, or leaves the site for an amount of
time equal to this time out value the session and all its
information will be lost. This value is 20 minutes by
default in IIS 5.0, but you can easily change it as
follows:
Session. timeout =x ‘x is the number of
minutes
Controlling session
• There are a number of reasons you may want to
change this value.
Let’s examine a typical web site: each user
that comes to the site gets a unique session
object which means each user gets his own
piece of the server’s memory . Even if he
leaves the site after only 30 seconds his
session is still alive for another 19 minutes
and 30 seconds. After a while this can add up
to a lot of memory.
• Table Slide table show the growth of session
with the default timeout value assuming 100
visitors come to your site every half hour and a
timeout value of 120 minutes.
Session
Time User Session Description
0:00 100 100
100 sessions are created for the first 100 site visitors.
0:30 100 200
The first 100 sessions are still active weather or not the
visitors are still on the site. 100 new visitors means 100 new
sessions.
1:00 100 300
Another 100 visitors adds 100 new session while the first two
group sessions still have not expired.
1:30 100 400
2:00 100 500
2:30 100 500
100 new visitors=100 new sessions
……..
100 new visitors create 100 new sessions but the first group’s
sessions finally expire after 2 hours.
3:00 100 500
It just keeps going and going……..
Session
• You have wasting a lot of memory 500
sessions for only 100 concurrent visitors.
This can definitely slow down the
operation of your whole site.
• You can also cause a session to expire
immediately by using the Abandon
method.
• Imagine a web site where user can check
their email. After a user is done he wants
to log out so that other people can not use
his e-mail account when he’s away from
his computer.
• Abandoning the session is one way to
accomplish this. Simply call the following :
Working with session
• The session object can be manipulated
just like an array. You can loop through all
the variables and manipulate them as
needed. Uses the for … each statement in
VB.NET to loop through and display the
contents of the session.
Session without cookies
• By default ASP.NET uses cookies to store session IDs and keep
track of the users. What happens however if the user’s browser
does not support cookies or the user just not accepting any? Luckily
ASP.NET has another way to keep track of sessions.
• New term- Cookie mugging is the process that ASP.NET uses to
keep track of sessions without cookies.
• Before a page Is sent to the browser ASP.NET scan the HTML code
for any hyperlinks. At the end of each link ASP.NET track on an
encoded version of the session ID.
• When the user clicks a link ASP.NET grabs that string decodes it
and passes it to the page the user is requesting.
• This page can now use that ID to set or retrieve any session
variables. ASP.NET also places the encoded session ID in each link
on this page as well. This all happens automatically if ASP.NET
detects that the visitor dose not support cookies.
Session (Cont…)
• Session (Cont…)
Do
Do use session variable s if
you have a small amount of
information for a single user
that you need to maintain for
the current session such as a
user name or password.
Don’t
Don’t use session variables
when you have a lot of
information to store for each
user. There are other
methods that won’t eat up
your server’s memory as
fast, such as cookies and
databases.
Using Session Variables
• We can create them and store data in them in
exactly the same way:
• // create a new Session variable to store the
users name
Session ( 'Name' ) = 'James';
• // display the name in any page on your site
Out ( 'Your name is ' + Session ( 'Name' ) );
• The crucial difference between Application and
Session variables is that Session variables are
specific to each visitor to the site.
Using Session Variables (Cont…)
• The stateless web:
• Session variables have to overcome the problem
that the HTTP protocol that we use to browse the
web is stateless
• Each request for a page is completely
independant of earlier requests, so if we want
subsequent pages to "remember" the users name
that the user entered on front page, we have to
store that information somewhere
• This remembering of user-specific data is called
"maintaining state"
Using Session Variables
(Cont…)
• Creating a new session:
• The first time a new user visits a page on site a
new session is automatically created
• cookies are simply data stored on computer and
automatically sent to the server by browsers
when requesting a page
• The first time a user visits, there's no cookie and
the server creates a new session and sets a
cookie with a unique value
• As the user browses site the cookie is sent back
and forth between computer and the server,
allowing the server to recognize the user
Using Session Variables
(Cont…)
• Unless we have cookies disabled, or are using a
browser that doesn't support them, we should see
something like ASPSESSIONID
• Tracking new sessions:
• The server tell us when a new session is created
by calling a function in global.asa file,
Session_OnStart( )
• use the Session_OnStart( ) function to
increment a count of how many users are
currently on site, or more accurately how many
active sessions there are -
Using Session Variables (Cont…)
• <script language=JavaScript runat=server>
function Session_OnStart ( )
{
// you must lock the global Application
object
// when writing to it - ok to read without
lock
Application.Lock ( );
// one more active user
Application ( 'ActiveUsers' )++;
Using Session Variables
(Cont…)
Ending a session:
• There are two ways to end a session
• 1. The user doesn't request or refresh a
page within a specific time period
2. Session.Abandon( ) is called from ASP
page
Sessions timing out:
• By default, if a user doesn't make any
requests from the server for 20 minutes
that session is ended. Similar to before, the
Using Session Variables
(Cont…)
• Setting timeout for the entire application:
• Timeout value can be changed for all pages by configuring IIS.
On earlier versions of IIS on Windows NT can be changed this
setting in the Internet Service Manager, but that was renamed
to the "Internet Information Services snap-in" in Windows 2000.
• To find the IIS snap-in: Control Panel / Administrative Tools /
Internet Services Manager and then view the properties for the
Default Web Site. On that dialog go to the Home Directory tab,
and choose the Configuration button. Choose the App Options
tab, and <phew> there's the setting!
Using Session Variables
(Cont…)
• Set it to as small a number as possible to increase
the efficiency of server. Set it larger than the time
users to read largest page, or they could lose their
session
• Setting timeout for a single session:
• We can override the timeout for a single session by
adding the following line into code –
• // this session will timeout after 5 minutes inactivity
Session.Timeout = 5;
Using Session Variables
(Cont…)
• Abandoning a session:
• We can end a session immediately by calling
Session.Abandon( ). The rest of the page is still
executed, and the Session object is still available for
that page, but the session is ended when the page
finishes executing.
• To stop processing immediately in a page, call
Response.End( )
• Note: Even though the session has ended, if the user
requests a new page from site a new session will
automatically start
Using Cookies
• A cookie is stored on the client's machine by their web browser
software. To set a cookie, include information in an
HttpResponse that instructs the browser to save a cookie on
the client's system
• Basic code for writing a Cookie in ASP.NET:
Using System.Web;
Response.Cookies["BackgroundColor"].Value = "Red";
• To read the cookie back:
Response.Write
(Request.Cookies["BackgroundColor"].Value);
• Note: For security reasons you can only read a cookie that was
set within the same domain name
Using Cookies (Cont…)
• To get a collection of stored items, such as user address details:
HttpCookieCollection cookies = Request.Cookies;
for(int n=0;n<cookies.Count;n++)
{
HttpCookie cookie = cookies[n];
Response.Write("<hr/>Name: <b>" + cookie.Name + "</b><br />");
Response.Write("Expiry: " + cookie.Expires + "<br />");
Response.Write("Address1: " + cookie.Address1+ "<br />");
Response.Write("Address2: " + cookie.Address2+ "<br />");
Response.Write("City: " + cookie.City+ "<br />");
Response.Write("Zip: " + cookie.Zip+ "<br />");
}
Creating cookies
• The response object allows you to create cookies easily.
There are two ways to create cookies:
– you can create multiple cookies each with a single value or
– you can create a single cookies with multiple key/value
pairs.
The following code snippet demonstrates both methods:
• ‘set up some cookie variables
• Response. Cookies(“ My Cookie”). Value=“ single cookie”
• Response. Cookies(“ 21dayscookie”)( “username”) = “Chris”
• Response. Cookies(“ 21dayscookie”)( “ preference”) = “800 *
640”
Accessing cookies
• The browser sends all cookies information to the server when it
makes a request. Therefore you can use the request object to
gather that information.
• Accessing a cookie follows the exact same syntax as creating a
cookie. In the following listing you will use response .write to the
cookie value to the browser:
‘set’ up some cookie variables
Response. write(Request. Cookies(“ my cookie”). Value)
Response. Write(Request. Cookies(“ 21dayscookie”) (“username”)
Response. Write(Request. Cookies(“ 21dayscookie”) (“preference”)
Again notice the difference between accessing a value and key/ value
pairs– specifically, the use of the value property.
Using Cookies (Cont…)
• We can get the details of cookies during
development, by turning on tracing in
ASP.NET. By adding Trace=“true”, within
the @Page directive at the start of the
page:
<%@ Page trace="true" language="c#"
Codebehind="page.aspx.cs"
Inherits="MyPage" %>
Using Application Variables
• Application variables are available to all pages on site, pages
that have the same application name. But they are gone
forever if the server is restarted
• To use Application variables write the statements like:
// to set the data
Application ( 'Data' ) = 'something';
// to use the data
Response.Write ( 'data is ' + Application ( 'Data' ) );
• We can use application variables for information including the
application name, background color, data source names, or
contact information
Using Application Variables (Cont…)
• A key reason that the Application object exists in
ASP.NET is for compatibility with classic ASP
code—to allow easier migration of existing
applications to ASP.NET.
• If we are creating an ASP.NET application from
scratch, store the data in static members of the
application class rather than in the Application
object.
• This will yield a performance increase over using
the Application object.
Using Application Variables (Cont…)
• Read/Write - We can add or modify items in code
while the application is running.
• To copy read-only code, set the variable's value
in the Application_Start event and then do not
change it anywhere else.
• Application variables are popular for storing
static items that need to be globally accessible
and yet modifiable at run time.
Using Application Variables
(Cont…)
• Application state
– variables are, global variables for each ASP.NET
application.
– We can share values of these variables throughout the
application.
– These variables are usually set in the
Application_OnStart event and then accessed and
modified in individual ASP.NET pages
– The lifetime of application variables spans through the
lifetime of the ASP.NET application until the application
is unloaded
Storing Session Variables in a
Database
• HTTP is a stateless protocol. To allow users save
to state information across requests, ASP.NET
provides Session storage.
• The session variables are stored on per-user
basis. In ASP.NET 2.0, we can customize the
session state store as per the requirement.
ASP.NET 2.0 and Session Storage:
• ASP.NET 2.0 allows user to store session
variables at three distinct locations:
1. In the memory of the Web server (in process)
Storing Session Variables in a
Database(Cont…)
2. In the memory of a machine dedicated to storing
session variables (state server)
3. In an SQL Server database
• The first mode is the default. Modes 2 and 3 are often
called "out-of-process" modes because the session
store is independent of the Web site
• Storing session variables in the SQL server has the
following advantages:
• Scalability: Web farm architecture can very easily
access the session variables because they are stores
in an independent database
Storing Session Variables in a
Database(Cont…)
• It is a much more scalable option than the others
• Reliability: Because the data is physically
persisted in a database, it is more reliable than
the other options. It has the ability to survive
server restarts
• Security: SQL Server is more secure than the inmemory or state server option. We can protect
data more easily by configuring SQL Server
security
Storing Session Variables in a
Database(Cont…)
• The session state mode can be configured via a
<sessionState> tag of the web.config file
• Note: In Web farm scenarios, the application path
of the Web site in the IIS metabase should be
identical in all the Web servers in the Web farm
• Session_End event never fires for any of the outof-process modes
Storing Session Variables in a
Database(Cont…)
Configuring SQL Server to Store a Session State:
• Before store a session state in SQL server, we need
to configure it. This configuration is done via a
command line tool called ASPNET_REGSQL.EXE.
We can store the session state in three possible
locations within the SQL Server:
– Temporary storage: In this case, the session
state is stored in the "tempdb" database of SQL
Server. The tool creates a database called
ASPState and adds certain stored procedures for
managing session to it.
Storing Session Variables in a
Database(Cont…)
– The tool also creates required tables in the "tempdb"
database. If we restart the SQL server, the session data is
not persisted
– Persistent storage: The tool creates a database called
ASPState and adds stored procedures for managing a
session to it. The session state is stored in the ASPState
database. The advantage of this method is that the data is
persisted even if we restart the SQL server
– Custom storage: Both the session state data and the
stored procedures are stored in a custom database. The
database name must be specified in the configuration file.
Storing Session Variables in a
Database(Cont…)
Disadvantages of Storing the Session
State in SQL Server:
• Performance: In terms of performance, a
SQL Server-based session store is possibly
the slowest option. Because session
variables are stored in a physical database,
it takes more time to get them in and out of
the database. This affects the performance
of Web site
• Cost: To store data in a SQL Server
database, we need to have a SQL Server
Storing Session Variables in a
Database(Cont…)
• Serializable data: This method requires that all
the data stored in session variables must be
serializable. Mark the classes as [Serializable] if
we want to store them in a session
Using the Cache Object
• Cache Object
– By using caching we can speed up processing
– There were also third-party options, like XCache
– The main benefits of caching are performance-related:
operations like accessing database information can be
one of the most expensive operations.
– If the database information is fairly static, this
database-information can be cached
– When information is cached, it stays cached either
indefinitely, until some relative time, or until some
absolute time
Using ASP.NET Output Caching
• Caching Options in ASP.NET:
ASP.NET supports three types of caching
for Web-based applications:
1. Page Level Caching (called Output Caching)
2. Page Fragment Caching (often called PartialPage Output Caching)
3. Programmatic or Data Caching
Using ASP.NET Output Caching
(Cont…)
• Page Level Caching/Output Caching:
– Caches the HTML output of dynamic requests to
ASP.NET Web pages
– ASP.NET implements this through an Output Cache
engine.
– Each time an incoming ASP.NET page request comes
in, this engine checks to see if the page being
requested has a cached output entry.
– If it does, this cached HTML is sent as a response;
otherwise, the page is dynamically turned and, its
output is stored in the Output Cache engine
– Output Caching is particularly useful when we have
very static pages
Using ASP.NET Output Caching
(Cont…)
• Page Level Caching/Output Caching (Conti..)
– Output caching can be implement in ASP.NET by simply
using the @OutputCache page directive
<%@OutputCache Duration="60" VaryByParam="none" %>
– The Duration parameter specifies how long, in seconds,
the HTML output of the Web page should be held in the
cache
– When the duration expires, the cache becomes invalid
and, with the next visit, the cached content is flushed,
– The ASP.NET Web page's HTML dynamically generated,
and the cache repopulated with this HTML
Using ASP.NET Output Caching
(Cont…)
• Page Level Caching/Output Caching (Conti..)
– The VaryByParam parameter is used to
indicate whether any GET (QueryString) or
POST (via a form submit with
method="POST") parameters should be used
in varying what gets cached (ie)
– multiple versions of a page can be cached if
the output used to generate the page is
different for different values passed in via
either a GET or POST
Using ASP.NET Output Caching
(Cont…)
Page Fragment Caching/Partial-Page Output Caching:
• Partial-Page Output Caching, or page fragment caching, allows
specific regions of pages to be cached
• ASP.NET requiring part(s) of the page we wish to have cached
appear in a User Control
• Since Output Caching caches the HTML of the entire ASP.NET
Web page, clearly Output Caching cannot be used for these
scenarios: enter Partial-Page Output Caching
• Contents of a User Control should be cached is to supply an
OutputCache directive at the top of the User Control
• The content inside the User Control will now be cached for the
specified period, while the ASP.NET Web page that contains
the User Control will continue to serve dynamic content.
Partial Page Caching
• Partial page caching allows user to cache parts of a
response.
• This mechanism is useful when pages contain
volatile content such as calculation results, static
content such as headers and footers.
• Partial page caching is supported by a tag library for
use in JSPs, and a public API for use in servlets
• The tag library implementation is provided in
CacheTags.jar, installed in the extensions
subdirectory of EAServer installation
Partial Page Caching (Cont…)
• To use the library in a JSP, add the following
directive:
<%@ taglib
url="http://www.sybase.com/EAServer/cachetags.tld"
prefix="ct"%>
• To cache a portion of a page, surround it with this tag,
as in:
<prefix:cache attributes>... page content
...</prefix:cache>
• Where prefix is the tag prefix that we assigned the
tag library when declaring it in the taglib directive
Partial Page Caching (Cont…)
• Using the caching API:
• We can call the caching API to cache
response parts in servlets. The API is
implemented by class CacheManager,
described below:
package com.sybase.jaguar.servlet;
public class CacheManager
• Allows user to cache responses or parts of
a response in Java servlets
Using ASP.NET Output Caching
(Cont…)
Note : that for this we should not place an
OutputCache directive in the ASP.NET Web page
that contains the User Control - just inside of the
User Control
Programmatic or Data Caching:
• Programmatic or data caching takes advantage
of the .NET Runtime cache engine to store any
data or object between responses (ie),
• we can store objects into a cache, similar to the
storing of objects in Application scope in classic
ASP
Using ASP.NET Output Caching (Cont…)
• Data cache is kept in memory and "lives" as long
as the host application does (ie), when the
ASP.NET application using data caching is
restarted, the cache is destroyed and recreated
• To store a value in the cache, use syntax like this:
Cache[“check"] = bar; // C#
Cache(“check") = bar ' VB.NET
• To retrieve a value, simply reverse the syntax like
this:
bar = Cache[“check"]; // C#
bar = Cache(“check") ' VB.NET
Using ASP.NET Output Caching
(Cont…)
• Since Data Caching uses an in-memory
cache, there are times when cache
elements may need to be evicted.
• To add an instance of the object bar to the
cache named foo, use syntax like this:
Cache.Insert(“Check", bar); // C#
Cache.Insert(“Check", bar) ' VB.NET
Using ASP.NET Output Caching
(Cont…)
• If we want to pull data out of an XML file, but don't
want to constantly go to disk to read the data, we can
tell the ASP.NET caching engine to expire the cached
XML file whenever the XML file on disk is changed.
To do this, use the following syntax:
Cache.Insert(“Check", bar, new
CacheDependancy(Server.MapPath("BarData.xm
l")))
• The cache engine takes care of removing the object
bar from the cache when BarData.xml file is changed
Using Dynamic Properties
• Using the power of dynamic properties, we can declare property
values not only as constants, but also as formulas. The formulas
used in a dynamic property can reference property values from
other elements, thereby allowing authors unique flexibility when
designing their Web pages
• Benefits of Dynamic Properties:
• Dynamic properties are similar to a spreadsheet's
implementation of a formula. In a spreadsheet, a cell's value can
be a constant or a formula. A formula can include references to
any number of other cells in the spreadsheet. Likewise, a
dynamic property can reference other properties on the same
document.
Using Dynamic Properties (Cont…)
• Dynamic properties enable Web authors to describe
relationships between objects, properties, and
variables in terms of functions, rather than specify
an explicit sequence of steps to follow
• Implementing Dynamic Properties:
• Dynamic properties are introduced through four new
methods:
1. The getExpression method returns the current
formula used for the dynamic property
2. The recalc method allows authors to explicitly
cause the values of dynamic properties to be
updated.
Using Dynamic Properties (Cont…)
3. The removeExpression method clears formulas set with the
setExpression method
4. The setExpression method specifies a formula for a given
value
• Dynamic property formulas are assigned in script with the
setExpression method. They can also be assigned inline
using the global possible value, expression, in the style block
or in the STYLE attribute
• Ex: Dynamic HTML (DHTML) can be used to position objects
based on the location and measurement of other objects.
• - Center the object horizontally:
object.style.left=(document.body.clientWidth/2) (object.offsetWidth/2);
Using Dynamic Properties (Cont…)
• - Center the object vertically:
object.style.top=(document.body.clientHeight/2) (object.offsetHeight/2);
• Note: For some earlier versions of Windows Internet
Explorer, the style object is not updated after using
setExpression or removeExpression until the
recalc method is called. For backwards compatibility,
always include a recalc after dynamically modifying
an expression
• The parameters of setExpression are first evaluated
by the scripting language engine
Using Dynamic Properties (Cont…)
• When specifying a string constant for a parameter of
setExpression, nest the constant in single quotes. The single
quotes force the parameter to be evaluated as a string
object.style.setExpression("backgroundColor","red");
• To allow the Cascading Style Sheets (CSS) parser to interpret
this string as the natural color constant "red", the string must be
wrapped in single quotes
object.style.setExpression("backgroundColor","'red'");
• Dynamic properties can be retrieved and removed using the
getExpression and removeExpression methods
Using Dynamic Properties (Cont…)
• The getExpression method returns a variant containing the
expression used to compute the dynamic property. This
expression is recalculated when the getExpression method is
invoked
• Expressions are cleared using the removeExpression method.
This method is the only way to clear dynamic property values set
with the setExpression method. When an expression is cleared,
the property value is equal to the last expression calculation and a
Boolean value is returned indicating whether the expression was
removed
Using Dynamic Properties (Cont…)
• The recalc method is used to recalculate dynamic properties
in a document. Calling recalc(true) will recalculate all
expressions in the current document, regardless of whether
referenced properties have been changed. After a dynamic
property has been recalculated, references to that property
will retrieve the new calculated value
• Notes on Implicit Dependencies:
• Implicit dependencies refer to properties that may be altered
by changes in other properties. For instance, the offsetWidth
of an element depends on the width and possibly even the
height value in a style sheet
View state
• The viewstate describe how an object looks at
that particular moment.
• An application that keeps track of this
information is said to maintain state.
• If you fill out an HTML form and come back to it
later chances are the fields you’ve filled out will
be empty.
• This is because the web is a stateless medium it
does not allow you to keep track of view state or
other such information.
View state (Cont…)
• This was often a pain for traditional ASP
developer because it required mechanism
to maintain and retrieve this information
ASP.NET makes this much easier.
• ASP.NET automatically keeps track of the
viewstate for you. This means that if you
fill out an HTML form and click submit the
value will still be there when the page
comes back!
• This is an important part of ASP.NET and
is integral to a number of different
mechanisms.
View state (Cont…)
• That string of the seemingly random character is ASP.NET
way of telling itself what each control looks like.
• When the form is submitted ASP.NET automatically retrieves
this string and uses it to fill out the form information again.
• ASP.NET uses the fact that browsers can only understand
HTML and writes itself reminders in the page that are send to
the client.
For example look at the following line written on the server:
<form runat =“server”>
This sends the following HTML code to the browser:
<form name =“ ctrl2”method = “post” action = “listing0201.aspx” id=“ctrl2”>
<input type =“hidden” name” __VIEWSTATE” value
=“YTB6LTEwNzAy0TU3NjJfX1949e1355cb”/>
• Viewstate management show cases ASP.NET focus on
making the web a more traditional application environment.
Thank You
Classification : Confidential