when they say the action controller in the struts framework is multi threaded, does it mean that there are multiple instances of the servlet taking the request and forwarding it to the model. OR does it mean that there is one single instance taking all the requests? Any visuals will be appreciated
A:
As per most other servlets, a separate thread is created to process each request. You have to implement the SingleThreadedModel interface to get a new instance of the servlet for each request.
John Topley
2008-09-20 13:00:19
+1
A:
see http://struts.apache.org/1.x/userGuide/building_controller.html
The Struts controller servlet creates only one instance of your Action class, and uses this one instance to service all requests. Thus, you need to write thread-safe Action classes. Follow the same guidelines you would use to write thread-safe Servlets. Here are two general guidelines that will help you write scalable, thread-safe Action classes:
Only Use Local Variables - The most important principle that aids in thread-safe coding is to use only local variables, not instance variables, in your Action class. Local variables are created on a stack that is assigned (by your JVM) to each request thread, so there is no need to worry about sharing them. An Action can be factored into several local methods, so long as all variables needed are passed as method parameters. This assures thread safety, as the JVM handles such variables internally using the call stack which is associated with a single Thread.
Conserve Resources - As a general rule, allocating scarce resources and keeping them across requests from the same user (in the user's session) can cause scalability problems. For example, if your application uses JDBC and you allocate a separate JDBC connection for every user, you are probably going to run in some scalability issues when your site suddenly shows up on Slashdot. You should strive to use pools and release resources (such as database connections) prior to forwarding control to the appropriate View component -- even if a bean method you have called throws an exception.
crowne
2009-04-29 14:55:50