I've been always trying to avoid using Sessions. I've used spring security or other ways of having user logged in the application, which is I suppose the major use case for using Sessions.
But what are the other use cases ? Could you please make a list of those most important ones ? How come that I've been able to develop even complicated applications without using Sessions?
Is it because I'm using spring-mvc and using Sessions is practically not needed except the login stuff ?
EDIT: Guys this question was asking for use cases... Most of the answers explains what are sessions for. If we summarize some usecases, we can say for sure, when to use database or sessions for maintaining conversation state...
Don't you remember any concrete scenarios you needed sessions for? For past years :)
for instance some conversational state may become persistent after some point / event. In this case I'm using database from the beginning.
I think you can do anything you want without storing anything on a sessions.
I usually use the sessions to avoid having to pass state between the client and server (used id as an example) and when I don't want to send sensitive information to the client (even in encrypted form) as it might be a security problem.
Other ways of avoiding using the session are:
store some state on a database, e.g. shopping carts, instead of in the session, even if the cart is discarded after a certain amount of time.
store state in cookies e.g. for user customization
One use case when it's really useful to use the session is for conversations, although usually frameworks manage that behind scenes, and store the conversation in the session.
edit
Converstions (in my understanding) are something like wizards, in which you complete several forms in different pages and at the end you perform the action. e.g. in a checkout process, the user enters his name, shipping address and credit card details in different pages, but you want to submit the order just at the end, without storing any intermediate state in your DB.
By sensitive information I mean, imagine in the previous example, once the user sent his credit card details, you shouldn't return that information in any format (even encrypted) to the user. I know it's a bit paranoid, but that's security :).
In the ecommerce system i'm working on, there is an external system at the back-end which stores users' saved shipping and billing addresses. Our web app talks to it by making web service calls to retrieve those addresses. When we get the addresses, we store them in the session. That way, we only have to call the service once, when the user firsts looks at their addresses, and not every time we serve a page which needs address information. We have a time-to-live on the addresses, so if the addresses change (eg if the user telephones the customer service desk to change an address), we will eventually pick up the fresh ones.
It would be possible to store the addresses in our database, rather than in the session. But why would we? It's transient information which is already stored permanently somewhere else. The session is the ideal place for it.
Well in one sense your question is deep (what's SPECIAL about a session is worth knowing) and in another sense it's shallow (what can't I do if I don't use them turns out to be a somewhat odd question)
In the end a Session is merely (or could be) a ConcurrentHashMap (in fact it usually isn't that threadsafe) with a a key of unique session id passing as the cookie. You know why it's useful, but to answer you for use cases
clustering (this is how state gets distributed across nodes)
caching general state of the user and their objects (as opposed to reloading from db each time)
built in methods for sessionlisteners to watch when someone is timed out, or attributes change.
= used for by a lot of localization utilities
Can you do all this with a database or your own hashmap implementation/filter? Of course, there's nothing magical about Sessions. They are merely a convenient standard for having some objects follow a logged in user and be tied to the lifetime of that user's use of the application.
Why do you use Servlets? You could also implement your own socket level standard? The answer to that is using standard apis/implementations provides convenience and other libraries build upon them.
The cons are
you are reinventing the wheel and some code that has been time tested
you won't be able to use a lot of built in facilities for monitoring/managing/clustering/localizing etc.
Sessions are one way of maintaining conversational state across multiple requests (e.g. multiple stateless HTTP requests.)
There are other ways of implementing conversational state, for example, storing an authentication token or some suitable conversation id as a cookie and maintaining a store of conversation id to session state. (In essence, duplicating what the app server is doing when it provides sessions.)
That you haven't needed to use sessions means that your application either doesn't need conversational state or you've implemented it in a different way. For example, perhaps your application uses an authentication token (say a cookie) and persists all state changes to the database. With that kind of arrangement, there is no need for a conversation state.
Hi you can take an example of shopping cart because since Http is stateless protocol it does not maintain the status of the user who sends the request.
For e.g.
If one user sends a request to buy camera from say eBay and after some minutes another user sends a request to buy laptop.
But since http is stateless protocol so server is not able to separate the request send by the users and may it happen that the bill of the laptop may be given to first user.
So through session we can maintain a particular entity over the server side for a particular user.
Related
When a user is interacting with a website, there's usually some object that could be considered the "current" object, like a shopping cart, or, to use an example in my world, a manufacturing job. What's the best practice for tracking that current object from page to page? I can think of a few:
put the ID as a request parameter (downside is security, since a
hacker could use that to change the URL to a different ID)
a session object (downside is if you have a huge amount of users
and/or the current object has a large memory footprint)
cookie? (Haven't tried that one)
Have I missed some obvious answer?
BTW, we're using Java, WebLogic and Struts1.
It really depends on your technology stack as to what "best practice" would be for you right now.
For example, if you're building a traditional Rails application using ERB templates without a MVC front end or anything, then I think that using the session object that the Rails framework provides for you would be best.
Most web frameworks will supply you an easy way to keep track of a particular user that's browsing the website. Most of the ones I've seen use a combination of your second and third options. They have a session ID that is stored as a cookie in the user's browser and every time that user sends a request to the web server, it loads a Session object from memory or the database using the session ID value that was stored in that cookie. Memory shouldn't be an issue unless you have an enormous number of users, but that also depends on the type of information that you're storing in there.
If you're storing entire database rows or records, and the sessions are being stored totally in memory, then maybe you should consider only storing the IDs to those records.
Research your particular web framework well to see how it handles user sessions.
As far as a cross-platform best practice, the Session object paradigm seems tot be the best approach to date. It permits matching of request parameters to tracking of sessions independent of the handling of the request parameter. An extension to this is that the Session object provides a handy place to put a collection of things for use if the session is re-identified (Java uses a Map).
Generally the Session is a representation of a single web browser visiting a single website repeatedly. Since there is nothing associating one request to another, this is generated synthetically from a combination of items, including user agent string, reply ip address, etc (in the past it was a stored value in a cookie, which caused no end to security issues).
Assuming you have a reliable Session object available, typically one stores the items that a supposed "single user" driving the session should have access to. So, if you have a shopping cart, it might be represented as a shopping cart object accessible from the session. In Java, that might be a map.
When identifying a new session
// request is a HttpServletRequest object in this example
if (request.getSession(false)) {
// must be a new one
Session newSession = request.getSession(true);
newSession.putValue("shoppingCart", new ShoppingCart());
}
Later on, when adding to the cart
ShoppingCart cart = (ShoppingCart)(request.getSession(false).getValue("shoppingCart"));
cart.addItem(item);
The benefits of separating out the detection from the request handling make it easy to fix / tweak session tracking without altering the code for the "session contents".
The other Answers are correct. Just a bit more explanation.
The Java Servlet technology’s Session object is indeed aimed at solving this exact problem, how to track a single user’s set of current objects over time, beyond the HTTP request-response lifecycle. This lends statefulness to an otherwise stateless protocol (HTTP). Every Servlet container (Tomcat, Jetty, WildFly, and so on) automatically handles the details such as using cookies or URL rewriting so you needn't worry about that.
Yes, as you add stuff to the Session object its memory usage grows in size. If running low on memory, your Servlet container such as Tomcat may choose to write an older Session object to storage using Serialization. The catch here is that all your objects in the Session must be serializable. Ensuring your classes (and all their nested objects) can correctly handle serialization can be a big chore.
Tip: If possible add memory to your server to more that handle your highest session load. As the wise man said, "Algorithms are for people who don’t know how to buy RAM.".
I am creating an app store for digital services. I want the user to be able to choose multiple products with different quantity before confirming the order and pay for the services. This requires that something keep state. From REST Wikipedia:
Each request from any client contains all the information necessary to service the request, and session state is held in the client.
I got state that I need to keep somewhere, and I also have a flow. The flow I can mange, but it is the state that I don't understand how and where I should store. The user may add several products to a shopping cart before checking out.
I have thought of a endpoint like this where you post a cart-item object each time you want something.
POST /shopping-cart
But I shouldn't use HTTP sessions if I understand it right? I have seen someone saying to store it in database but would you use a in memory database then? When should i flush the database if the user doesn't confirm and pay? I could need some input on what I should do to keep it simple and RESTful.
I am using Spring 4.x and Java EE for the record.
But I shouldn't use HTTP sessions if I understand it right?
Correct.
I have seen someone saying to store it in database but would you use a in memory database then?
You should keep in in a disk-storage database. This allows you to add nodes to your server without having to worry about routing all requests from one client to the same node.
When should i flush the database if the user doesn't confirm and pay?
That's a business decision.
I am trying to learn more about JAVA web development. I am mainly focused on trying to understand how data that a user enters, maybe through the course of filling out a multipage form, is managed as the user moves from page to page.
From what I have gathered, you can store data within the session on the server side. I am also learning about cookies which are stored within the browser. Is there a general rule that is used to determine what data should be stored in a cookie vs. when you should store data in a session (session.setAttribute), or are these completely different concepts?
Thanks
The basics of session/cookies are like this.
A session is typically a way for a server to store data about a user. This can be done in a variety of ways from memory, file to database. This session can be used by you store pretty much anything you need to have as the user bounces around your site. It is assigned an ID (the session ID) which you don't usually need to worry about too much. In most web languages you can easily access the user session with some functions without dealing with IDs.
Now since the web is stateless - meaning there is really no way to know that user that visited page A is the same as the one that visited page B then we want to make sure that the user carries their session IDs with them. This can be done in a variety of ways but the most common one is through the use of a session cookie which is a special cookie automatically set by the server that is solely there for passing the session around. It can also be passed in the URL (I'm sure you've seen things like index.php?sessid=01223..) as well as headers and so on.
When most people talk about adding info to a cookie they are not talking about session cookies but about a custom cookie that you specifically set. The only reason that you would want to do that is if you needed to store info beyond the life of the session (which ends when the browser is closed). A good example of that is the "remember me" feature of many sites.
So use sessions unless you need to have something last a long time.
Yes. There are a few rules actually. For one, cookie data is sent by the browser on every request; session data is kept on the server (and not re-transmitted every request). However, usually the session id is used with a coookie. This enables the server to identify the client.
I have a login page which connects to a Database, the Database has only one client, when a user logs on he/she may make certain changes to his profile and then save. A large number of frames require the current user id in order to manipulate his data
Among the possible ways of storing the user currently logged in is
1) to save the data to a temporary text file and persist it before the user logs out
2) another option would be to use variables across all the frames ,however I'm not too confident about this
3) a third way would be to have a Boolean column in the database and to persist the the data of the field with true in it
Perhaps there are better ways of storing the current user Id could somebody elucidate other possible methods and highlight the pros and cons of each implementation with reference to an "optimal" method of doing this
Edit: This is a desktop application
I would suggest not to share this information in any static context for the reason it will render your project as very hard to test once it gets big enough. See this link for more info: When to use singletons, or What is so bad about singletons?
What I would do is store session objects in some map, identifying the appropriate session by an ID that will be given and sent back to you via client cookie. This is how the web has been doing it for years, and it is still doing it this way. Simply pass the session object around to any class that requires access to that data when it needs it.
If you are using a J2EE implementation, then you may already have support for sessions within that implementation, you should check out "How to Use Sessions"
This is more of a software design question, and covering the basis to complete the patterns used to support what I just suggested is unfortunately beyond the scope of the question
The logged user is an instance of the class Person or LoggedUser.
You have to instantiate it and share its reference between Views via a Model.
In our web application (in JBoss using Struts) we use sessions largely for security as well as to cache some data for a User. Thus, every user logged into the application has a session and different data cached in it.
Based on some parameter change, i want to change the cache of the subset of users who are logged in (i.e. have session)
Can this be achieved? I have not been able to find anything so far from general search.
You can use a HttpAttributeListener
a basic example here
HttpSessionAttributeListener:
The HttpSessionAttributeListener interface enables an object to
monitor changes to the attribute lists of sessions within a given Web
application. The HttpSessionAttributeListener in turn extends
java.util.EventListener. The methods in it are
attributeAdded(HttpSessionBindingEvent se)- This is the notification that an attribute has been added to a session.
attributeRemoved(HttpSessionBindingEvent se)- This is the notification that an attribute has been removed from a session.
attributeReplaced(HttpSessionBindingEvent se)- This is the notification that an attribute has been replaced in a session.
You can do it by storing each session object in a static List<Session> in some holder object. You can put it by a HttpSessionListener#sessionCreated(..). Remember to remove it from the list on sessionDestroyed(..)
Then, whenever you want to do something, simply loop the previously stored list of sessions and do whatever you want with them.
You have basically 2 options:
Push the changes. Get hold of all HttpSession instances in an application wide map which you manage with help of a HttpSessionListener. This way you can just get them from the application scope and walk through them to make the necessary changes directly.
Poll the changes. Store a change instruction in the application scope. On every HTTP request, check with help of a Filter or ServletRequestListener if a change is required, then make the necessary change in the current session and remove/disable the change instruction.
A completely different alternative is to use an application wide shared cache, such as Terracotta or Ehcache, so that you don't need to duplicate the same data over all HTTP sessions. You'd just need to deal with the data on a per-request basis. When database access comes into picture with JPA, then read on about "2nd level cache", that's exactly what it does.