what does it mean when they say http is stateless
I am studing java for web and it mentions http is stateless. what does that mean and how it effects the programming
I was also studying the spring framework and there it mentions some beans have to declared as inner beans as their state changes . What does that means?
Answer
HTTP -- that is the actual transport protocol between the server and the client -- is "stateless" because it remembers nothing between invocations. EVERY resource that is accessed via HTTP is a single request with no threaded connection between them. If you load a web page with an HTML file that within it contains three <img> tags hitting the same server, there will be four TCP connections negotiated and opened, four data transfers, four connections closed. There is simply no state kept at the server at the protocol level that will have the server know anything about you as you come in.
(Well, that's true for HTTP up to 1.0 at any rate. HTTP 1.1 adds persistent connection mechanisms of various sorts because of the inevitable performance problems that a truly stateless protocol engenders. We'll overlook this for the moment because they don't really make HTTP stateful, they just make it dirty-stateless instead of pure-stateless.)
To help you understand the difference, imagine that a protocol like Telnet or SSH were stateless. If you wanted to get a directory listing of a remote file, you would have to, as one atomic operation, connect, sign in, change to the directory and issue the ls command. When the ls command finished displaying the directory contents, the connection would close. If you then wanted to display the contents of a specific file you would have to again connect, sign in, change to the directory and now issue the cat command. When the command displaying the file finished, the connection would again close.
When you look at it that way, though the lens of Telnet/SSH, that sounds pretty stupid, doesn't it? Well, in some ways it is and in some ways it isn't. When a protocol is stateless, the server can do some pretty good optimizations and the data can be spread around easily. Servers using stateless protocols can scale very effectively, so while the actual individual data transfers can be very slow (opening and closing TCP connections is NOT cheap!) an overall system can be very, very efficient and can scale to any number of users.
But...
Almost anything you want to do other than viewing static web pages will involve sessions and states. When HTTP is used for its original purpose (sharing static information like scientific papers) the stateless protocol makes a lot of sense. When you start using it for things like web applications, online stores, etc. then statelessness starts to be a bother because these are inherently stateful activities. As a result people very rapidly came up with ways to slather state on top of the stateless protocol. These mechanisms have included things like cookies, like encoding state in the URLs and having the server dynamically fire up data based on those, like hidden state requests, like ... well, like a whole bunch of things up to and including the more modern things like Web Sockets.
Here are a few links you can follow to get a deeper understanding of the concepts: