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Java Forum / General / December 2005Running 2 webapp in Tomcat - 1 or 2 JVMs
Hi, If I run 2 web applications in a Tomcat, is that 2 web application run by 2 JVMs or 1 JVM? Regards, James Hello 1 JVM.I suppose it is virtual > Hello > 1 JVM.I suppose it is virtual Thanks. Does that means that it is impossible to implement RMI between them, since RMI requires at least 2 JVM to work? Regards, James i believe, if you are under 1 jvm you would be able to share objects between the two contexts. things to try (in any order of preference) 1) you might have to write a patch and alter tomcat to add a hook into the bootstrap to do this "under the table".. 2) the more appropriate way would be to do it "above the table", and have a servlet to servlet communication through a post/get... assuming the table is conceptually at the context level. 3) another possibility i just thought of, is to do this via jndi. that's kinda the purpose of it. and probably the best solution. 4) run two seperate jvm's and then rmi would make more sense. www.binaryfrost.com >1) you might have to write a patch and alter tomcat to add a hook into >the bootstrap to do this "under the table".. a garden variety static class will let anyone communicate with anyone in a JVM.  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. On Tue, 29 Nov 2005 02:37:28 GMT, Roedy Green <my_email_is_posted_on_my_website@munged.invalid> wrote, quoted or indirectly quoted someone who said : >a garden variety static class will let anyone communicate with anyone >in a JVM. More precisely the static variables of a garden variety class will let anyone communicate with anyone within a JVM. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > More precisely the static variables of a garden variety class will let > anyone communicate with anyone within a JVM. Depends ... if the different web applications are loaded via different class loaders then statics do not work. Also, RMI has its use also in a VM. Using RMI makes sure that you do not share any member between apps, really important if you want to unload apps dynamically, like OSGi. Kind regards, Peter Kriens OSGi Evangelist > On Tue, 29 Nov 2005 02:37:28 GMT, Roedy Green > <my_email_is_posted_on_my_website@munged.invalid> wrote, quoted or [quoted text clipped - 8 lines] > Canadian Mind Products, Roedy Green. > http://mindprod.com Java custom programming, consulting and coaching. > On Tue, 29 Nov 2005 02:37:28 GMT, Roedy Green > <my_email_is_posted_on_my_website@munged.invalid> wrote, quoted or [quoted text clipped - 5 lines] > More precisely the static variables of a garden variety class will let > anyone communicate with anyone within a JVM. Hi Roedy, I am not sure how a static class can help web app A calling and getting results from web ap B. Can you give an example? Regards, James >I am not sure how a static class can help web app A calling and getting >results from web ap B. Can you give an example? In a very simple example: public class Common { public static string share; } A has code like this: Common.share = "I will meet you at the casbah"; B has code like this: if ( Common.share != null ) ... In a real example A and B could call methods of Common and Common would call methods in the concurrent package. See http://mindprod.com/jgloss/queue.html SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > >I am not sure how a static class can help web app A calling and getting > >results from web ap B. Can you give an example? [quoted text clipped - 17 lines] > would call methods in the concurrent package. See > http://mindprod.com/jgloss/queue.html Hi Roedy, Thanks for the explanation Regards, James > i believe, if you are under 1 jvm you would be able to share objects > between the two contexts. [quoted text clipped - 13 lines] > > www.binaryfrost.com Hi cbroussard, Your recommendation is very valuable. I will start to look into the jndi solution. Regards, James >Does that means that it is impossible to implement RMI between them, since >RMI requires at least 2 JVM to work? the R in RMI stands for Remote. It jumps through hoops because sender and receiver are in different JVMS. When they are in the same JVM you can simply and efficiently past references back and forth. Typically, RMI involves at least three JVMs, a RMI server, an RMI application server and a client. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. >>Hello >>1 JVM.I suppose it is virtual [quoted text clipped - 3 lines] > Does that means that it is impossible to implement RMI between them, since > RMI requires at least 2 JVM to work? It probably does mean that you cannot do RMI between the two apps, but I'm not certain of it. A better question for you to think about, however, is whether it makes sense to split things up into two web applications in the first place when they are tightly enough bound together that you /want/ to do RMI between them. SignatureJohn Bollinger jobollin@indiana.edu > It probably does mean that you cannot do RMI between the two apps, but > I'm not certain of it. A better question for you to think about, > however, is whether it makes sense to split things up into two web > applications in the first place when they are tightly enough bound > together that you /want/ to do RMI between them. Hi John, The 2 web application serves different purposes but web app A requires some information from web app B. So for my case, it make sense to split them, and to communicate via RMI. However I also forsee a possibility that they may be hosted in the same container. Hence my questions in this threads. I will probably code some functions to allow switching of RMI with an alternative solution that is recomended in this thread. Regards, James >>It probably does mean that you cannot do RMI between the two apps, but >>I'm not certain of it. A better question for you to think about, [quoted text clipped - 13 lines] > I will probably code some functions to allow switching of RMI with an > alternative solution that is recomended in this thread. I personally would prefer a solution that works all the time. I see two alternatives that look reasonable: 1) App A obtains the needed information from app B through appropriate methods on B's web interface. If you like buzz words, you could describe this as B providing a web service that A uses. This approach makes sense if providing the required information falls in, or close to, B's general area of operation. 2) App A and app B share a common back end with which they both communicate, but which is logically separate from either. They don't communicate directly. The back end might be as simple as a common database, or as complex as a full-blown J2EE application comprising one or more EJBs, etc. A simpler RMI-based back end would fall in the middle, and there are other alternatives as well. I don't particularly care for the idea of B providing a back-door interface for A to use to get a hold of information that B just happens to be holding (though it's not clear whether that's what you were asking about). SignatureJohn Bollinger jobollin@indiana.edu > I personally would prefer a solution that works all the time. I see two > alternatives that look reasonable: [quoted text clipped - 16 lines] > to be holding (though it's not clear whether that's what you were asking > about). Hi John, I think I like solution A better. Thanks for the advice. I have been trying to look for information about doing a custom JDNI solution, but couldn't get the revelant information. So I will go back and look at XML solutions Regards, James Why not use something like SOAP or XML-RPC? That way it work the same on one JVM, two JVMs or remotely on a completely different server. >>Hello >>1 JVM.I suppose it is virtual [quoted text clipped - 6 lines] > Regards, > James Hello 1 JVM.I suppose it is virtual >If I run 2 web applications in a Tomcat, is that 2 web application run by 2 >JVMs or 1 JVM? One. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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