Class 38
- 1. Topic: 1. Sessions 2. Session Tracking 3. Session Management 4. Cookies 5. Filters 6. File downloading Servlets1
- 2. Session A session is pretty much what it sounds, when a user makes a page request to the server, the server creates a temporary session to identify that user. So when that same user goes to another page on that site, the server identifies that user. A session is a small and temporary unique connection between a server and the user enabling it to identify that user across multiple page requests or visits to that site. 2
- 3. 1. What is Session Tracking? There are a number of problems that arise from the fact that HTTP is a "stateless" protocol. In particular, when you are doing on-line shopping, it is a real annoyance that the Web server can't easily remember previous transactions. This makes applications like shopping carts very problematic: 3
- 4. when you add an entry to your cart, how does the server know what's already in your cart? Even if servers did retain contextual information, you'd still have problems with e- commerce. When you move from the page where you specify what you want to buy (hosted on the regular Web server) to the page that takes your credit card number and shipping address (hosted on the secure server that uses SSL), how does the server remember what you were buying? 4
- 5. There are three typical solutions to this problem. Cookies. You can use HTTP cookies to store information about a shopping session, and each subsequent connection can look up the current session and then extract information about that session from some location on the server machine. This is an excellent alternative, and is the most widely used approach. 5
- 6. 2.URL Rewriting. You can append some extra data on the end of each URL that identifies the session, and the server can associate that session identifier with data it has stored about that session. This is also an excellent solution, and even has the advantage that it works with browsers that don't support cookies or where the user has disabled cookies. 6
- 7. 3) Hidden form fields. HTML forms have an entry that looks like the following: <INPUT TYPE="HIDDEN" NAME="session" VALUE=".. .">. This means that, when the form is submitted, the specified name and value are included in the GET or POST data. This can be used to store information about the session. 7
- 8. Servlets provide a solution: the HttpSession API. This is a high-level interface built on top of cookies or URL- rewriting. In fact, on many servers, they use cookies if the browser supports them, but automatically revert to URL-rewriting when cookies are unsupported or explicitly disabled. But the servlet author doesn't need to bother with many of the details, doesn't have to explicitly manipulate cookies or information appended to the URL, and is automatically 8
- 9. Why use Session Management ? Hundreds and thousands of simultaneous users can be visiting your site and if you can identify each of them separately then it can provide tremendous benefits to you. 9