In the previous chapter we took a look at how the HTTP Request can help us move data from the JSP to the Servlet and vice versa and the methods that are available in the Request object that would help us handle the data it carries.
In this chapter, we are going to look at the Session which is a super-set of the request and can contain data that needs to be retained across different pages.
So, lets get started!!!
The HTTP Session:
The Session is the place where data can be stored and retrieved across multiple hits from the same browser for a certain period of time. For example, lets say you want to login to your online banking website and the browser asks you to enter your login id and password after every click? It would be irritating isn’t it?
Thankfully we have the Http session.
When we logon to our bank website and enter our login id and password, the application saves our credentials in the session and uses it when we navigate between screens on the banks website.
Note: For reasons of safety and security, usually sessions in sensitive websites like a bank website or a stock brokers site, the session expires automatically after 5 minutes of inactivity or if the user presses the back or refresh buttons.
Getting the Session Object:
The session object can be obtained from the Request using the below line of code:
HttpSession session = request.getSession();
Setting & Getting Attributes from the Session:
We can set and retrieve attributes from the session using the setAttribute & getAttribute methods.
session.setAttribute(“Key”, value); //Setting the value
Object obj = session.getAttribute(“Key”); //Getting the value
Here, “Key” is the identifier that will be used to locate the value saved in the session. The “Key” can be used to retrieve the value using the getAttribute() method.
Other Session Methods:
Some other methods available in the Session are:
1. getId() – Every session has a unique id and this method is used to get that id
2. getCreationTime() – To find out when the session was created
3. getLastAccessedTime() – To find out when the session was accessed last
4. getAttributeNames() – To retrieve all the values stored in the session as an Enumeration
To wrap up, sessions are what you can use to track a single user over a short time period (say 5 or 10 mins usually). You get the session object (HttpSession) from the request object. To track multiple users in your application, you can use the Context. Don't worry, that's our next stop…
For now, this chapter is over!!!
Previous Chapter: Chapter 14 - The Request Object
Next Chapter: Chapter 16 - Servlet Context
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