Java.Servlet.What is session ?

✅ “Session” in web development means:
A way to remember a user’s data between different HTTP requests.

Because HTTP is stateless by design:

• Every request is independent.
• The server doesn’t remember if two requests come from the same user.

So a session is like giving the user an invisible ID badge, so the server can recognize them across multiple requests.

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✅ Example:

1. You log into a website → the server creates a session for you.
2. The server stores your info in memory: cssCopyEdit

Session ID: X123ABC
Data: { username: "Stanley", role: "admin" }

1. The server gives you a session ID (either as a cookie or inside a URL).
2. Every next request you make includes your session ID, and the server finds your session in memory.

Result: You stay logged in, your cart stays full, etc.

✅ In Java Servlets:

• Session is represented by HttpSession object.
• You can get the session like this:

HttpSession session = request.getSession();
session.setAttribute("username", "Stanley");

Now “Stanley” is stored in the server’s memory under your session ID.

Later, you can retrieve it:

String username = (String) session.getAttribute("username");

✅ Where the Session ID is stored?

• Normally in a cookie (JSESSIONID).
• If cookies are disabled, it can be passed in the URL (;jsessionid=...).

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✅ Session Lifetime:

• Sessions live for a time (like 30 minutes of inactivity).
• After that, they expire (the server deletes them).
• You can also manually destroy a session:

session.invalidate();

✅ Real life analogy:
Imagine visiting a hotel:

• You check in at the lobby → they give you a room keycard (= session ID).
• Every time you enter your room, you use the keycard → hotel knows it’s you.
• If you lose the keycard, you can’t get back in (session lost).

✨ Quick Visual:

Request #	Without session	With session
1	Hello, who are you?	Hello, welcome back Stanley!
2	Hello, who are you?	Hello again Stanley!
3	Hello, who are you?	Hello again Stanley!

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Summary:

• A session allows the server to remember a user across multiple requests.
• It stores small data (like login info, shopping carts, etc.) server-side.
• It uses session IDs to connect requests to the correct user.