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Java Forum / General / March 2006Static methods thing
hi , can anyone tell me that when i declare field or method as static, whether for each user who connect to the server we have a static method or we have one static method for all users in the same server and that static method is shared between all users ? -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 NotDashEscaped: You need GnuPG to verify this message vahid.xplod@gmail.com schreef: > hi , can anyone tell me that when i declare field or method as static, > whether for each user who connect to the server we have a static method > or we have one static method for all users in the same server and that > static method is shared between all users ? There is one method bound to the class. So al long as you don't start doing things with ClassLoaders, you will only have one method. Per JVM, that is. H.  SignatureHendrik Maryns ================== www.lieverleven.be http://aouw.org Well I am not 100% sure because I do not know how your application is working. With a static you have one item for all instances of a class. Hence if you have one java application and one VM serving all users, then all users have that one static, since there is one static in the application. If you start a different VM for each request, which is more common, you have one static per session, and hence more or less one per user. Marcus Wentink > Well I am not 100% sure because I do not know how your application is > working. With a static you have one item for all instances of a class. [quoted text clipped - 3 lines] > more common, you have one static per session, and hence more or less > one per user. "If you start a different VM for each request, which is more common, ..." Did you really meant that? For what kind of "request" is it common to "start a different VM" ? <lewmania942@yahoo.fr> schreef > "If you start a different VM for each request, which is more common, > ..." > Did you really meant that? No, you are right, I was mistaking. The rest was quite valid though I think? >> Well I am not 100% sure because I do not know how your application is >> working. With a static you have one item for all instances of a class. [quoted text clipped - 10 lines] > > For what kind of "request" is it common to "start a different VM" ? I wouldn't be too surprised if I found out a particular server did this. While performance may take a hit, it leads to the server as a whole being much more robust to erroneous JSP code. You might even be able to set it up so that there's a seperate JVM for each web app (i.e. so that you and I both share the same server, if I write buggy code, it won't break your code). - Oliver > I wouldn't be too surprised if I found out a particular server did > this. I'd like to know of one that does, for security reasons, not performance. >> I wouldn't be too surprised if I found out a particular server did >> this. > > I'd like to know of one that does, for security reasons, not > performance. Out of curiosity, are you saying that having a seperate VM per request/app/whatever poses a security risk? If so what, risk might that be (other than denial of service attacks, which in the end are actually a performance issue)? - Oliver > Out of curiosity, are you saying that having a seperate VM per > request/app/whatever poses a security risk? Not at all. I'd like to provide JSP capability to people using a shared web server, but the only servers I know about use a single JVM, and I can't have that for security reasons. > Not at all. I'd like to provide JSP capability to people using a shared > web server, but the only servers I know about use a single JVM, and I > can't have that for security reasons. You should find each web app has a different class-loader, much like different web pages of applets. Tomcat, and I believe other Servlet containers, allow individual security policies. The difficulty comes in that Servlet containers and the class-loader mechanism aren't really optimised to do this sort of thing on a large scale. Tom Hawtin SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ > hi , can anyone tell me that when i declare field or method as static, > whether for each user who connect to the server we have a static method > or we have one static method for all users in the same server and that > static method is shared between all users ? You only have one static method per classloader (or is that per JVM?) But that is irrelevant because even if it were an instance method all callers get their own copy of the local variables declared within, so the distinction between static and instance method is not important. What is important is that you realise a servlet by default is multithreaded and exists as a single instance. Therefore attributes and static members are shared amongst all users. You used to be able to declare a single threaded model, where a servlet instance was created for each request, it was then intrinisically thread safe. But to answer your question simply, all users get there own copy. -- Mike W > hi , can anyone tell me that when i declare field or method as static, > whether for each user who connect to the server we have a static method > or we have one static method for all users in the same server and that > static method is shared between all users ? As you may have noticed, you've been getting mixed replies to this question, and that is because it depends largely on how your server and framework is configured. It's best to design your code so that you do not depend on on this behaviour one way or the other. If you need to share data between users, consider storing that data in a database, for example. - Oliver Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. 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