asp.net interview: How to pass values between pages?
Every interviewer will expect this from you. There are several methods to pass values from one page to another page. Described below are few methods to pass values between pages:
QueryString - The QueryString method of passing values between web pages is one of the oldest methods of passing values between pages. A variable value is properly encoded before it is placed on a querystring. This is to make sure that characters that cause problems (like symbols and spaces) are encoded correctly. See the code below to see how QueryString functionality works.
//Code in InitialPage.aspx
String sString;
sString = Server.UrlEncode("string in InitialPage.aspx");
Response.Redirect("DestinationPage.aspx?Value=" & sString);
//Code in DestinationPage.aspx reads the QueryString
String sString;
sString = Request.QueryString("Value");
Response.Write("Your name is " & sString);
The data in the DestinationPage.aspx in the URL looks like this...
http://www.dotnetuncle.com/DestinationPage.aspx?Value=dotnetUncle
Context - The context object is used to send values between pages. Its similar to the session object, the difference being that, the Context object goes out of scope when the page is sent to a browser. Example code below shows how to use Context object.
'InitialPage.aspx stores value in context before sending it
Context.Items("MyData") = "dotnetuncle";
Server.Transfer("DestinationPage.aspx");
'DestinationPage.aspx retrieves the value from InitialPage.aspx's context
String sString;
sString = Context.Items("MyDate").ToString;
Response.Write("The data is as follows: " & sString);
Session - The session object is used to persist data across a user session during the user's visit to a website. It is almost same as the Context object. When we use Response.Redirect, it causes the Context object to go away, so rather the Session object is used in such a scenario. Session object uses more of server memory than a context object. Example code below shows how to use Session object.
'InitialPage.aspx stores value in session before sending it
Session.Items("MyData") = "dotnetuncle";
Response.Redirect("DestinationPage.aspx");
'DestinationPage.aspx retrieves the value from InitialPage.aspx's session
String sString;
sString = Session.Items("MyDate").ToString;
Response.Write("The data is as follows: " & sString);
ASP.NET Interview Questions: Different States in ASP.NET
You can see that a browser on the client side requests a page from the web server. After processing the request and returning the page, the server drops the connection. Then. if the browser makes another request the server has no way to associate the browser with the previous request. So HTTP is called as a stateless protocol. But ASP.NET provides several ways to maintain the state.
View State
View state is used to maintain the values of server control properties. AS ASP.NET implements view state by default you need not to write any special code to use it.
Session State
Session state is used to maintain data between execution of an application. For this, ASP.NET creates a session state object that is kept on the server whenever a user starts a new session. The session state object contain unique session ID, and this ID is sent back and forth between the server and browser each time the user request a page. Then when the server receives a new request from the user, it can retrive the right session state object for that user. You can add data items to the session object in your code, so there previous values are available each time a web form is executed.
Application State
ASP.NET provides an application state object to save application state data, which applies to all the users of an application. You can use application state object to manage global counters to maintain a list of users who are currently logged on to an application.
Profile
ASP.NET also provides profile feature to keep track of user data. Although a profile is similar to session state object, it persists between user session as it is stored in a database. For example we can use profiles we can keep track of the products ordered by an user in an shopping application and when the user starts a new session, you can display those products in a "ordered items" listbox.
How will ASP.NET handle session management?
"ASP.NET does not rely on SQL Server or LDAP for session management. Basically we provide two new additional features: 
1.) Cookieless Session: This is where we "munge" the sessionid into URLs as opposed to client-side cookies to keep track of SessionIDs (enabling you to now use session state even with browsers that have cookie support disabled). We automatically do the munging for you (no code changes required) to make this happen for both static and dynamic content (so you can link off to a static html page which then in turn links off to another dynamic page -- and the session is maintained).
2.) External Session State Support. This is where we store session values into an external state store instead of the ASP.NET worker process. This guaretees that state is stored accross worker process restarts (providing great reliability) as well as accross multiple machines (providing built-in web farm support). We ship support for two session stores out of the box: 1) the "ASP.NET state store" which is a dedicated NT Service that can run on any box -- and which ships with the ASP.NET bits. 2) support for storing session data directly into SQL Server. This later option is more scalable -- but does require you to buy SQL Server in order to make it work.
"Note that the above two state options are completely orthoganal from each other -- ie: you can use them together or separately. Also, our external state store support is pluggable -- meaning that we expect other third parties (as well as people like MS Commerce Server) to plug in their own store support into the model.
"With regard to performance, we are *much* faster than than existing pre-ASP.NET state solutions when doing out of proc state. We are leveraging ASP.NET's new MTA based thread pool to do async read/write operations that enable us to avoid blocking worker threads when retrieving and updating the state (instead using iocompletions to reuse threads). This should improve system throughput significantly and was not possible before with ASP (since it used an STA thread pool and as such couldn't do async operations)."
How can I enable session tracking for JSP pages if the browser has disabled cookies – jsp interview questions
We know that session tracking uses cookies by default to associate a session identifier with a unique user. If the browser does not support cookies, or if cookies are disabled, you can still enable session tracking using URL rewriting. URL rewriting essentially includes the session ID within the link itself as a name/value pair. However, for this to be effective, you need to append the session ID for each and every link that is part of your servlet response. Adding the session ID to a link is greatly simplified by means of of a couple of methods: response.encodeURL() associates a session ID with a given URL, and if you are using redirection, response.encodeRedirectURL() can be used by giving the redirected URL as input. Both encodeURL() and encodeRedirectedURL() first determine whether cookies are supported by the browser; if so, the input URL is returned unchanged since the session ID will be persisted as a cookie.
Consider the following example, in which two JSP files, say hello1.jsp and hello2.jsp, interact with each other. Basically, we create a new session within hello1.jsp and place an object within this session. The user can then traverse to hello2.jsp by clicking on the link present within the page. Within hello2.jsp, we simply extract the object that was earlier placed in the session and display its contents. Notice that we invoke the encodeURL() within hello1.jsp on the link used to invoke hello2.jsp; if cookies are disabled, the session ID is automatically appended to the URL, allowing hello2.jsp to still retrieve the session object. Try this example first with cookies enabled. Then disable cookie support, restart the brower, and try again. Each time you should see the maintenance of the session across pages. Do note that to get this example to work with cookies disabled at the browser, your JSP engine has to support URL rewriting.
hello1.jsp
<%@ page session=\"true\" %>
<%
Integer num = new Integer(100);
session.putValue("num",num);
String url =response.encodeURL("hello2.jsp");
%>
<a href=\'<%=url%>\'>hello2.jsp</a>
hello2.jsp
<%@ page session="true" %>
<%
Integer i= (Integer )session.getValue("num");
out.println("Num value in session is " + i.intValue());
%>
