问题
I'm working on a JSF 1.2 project which has AJAX functionality on it's pages (using RichFaces).
My bean builds a list of objects to be edited and then has methods to support the editing and the bean is session-scoped. I will be using a a4j:queue so that only one AJAX call can happen at a time.
I'm curious if it is wise to use synchronization (locks on objects, or perhaps collections from java.util.concurrent) in the managed bean. Is the extra work needed to implement synchronization/thread safety really needed? The site I am working on has many users and needs to be reliable but it has a LOT of managed beans, and I'm curious how concerned I should be about the thread safety of managed beans overall.
Do you take extra steps in backing beans for thread-safety?
Thanks in advance.
回答1:
a4j:queue won't prevent the user from reloading the page / clicking another link while the AJAX call is in progress.
Yes, we can probably trust the user not to click many different links right after each other, but what about requests not triggered by the user, for instance by a4j:poll?
Note that replacing all collections with their thread-safe equivalent might not be enough to make your application thread safe.
That said, depending on the degree of reliability your application needs to meet, this problem might or might not deserve your attention.
回答2:
You need to keep scope in mind.
Request scope - thread safe, session scope - not thread safe
If you need to be able to open multiple browser windows or tabs, then you can use something like a Seam conversation to protect from editing the same object from two windows/tabs.
回答3:
If it is SessionScoped you must take care to use some thread-safety mechanisms. If it is RequestScoped or ViewScope'd, then it is safe to share class variables between methods.
来源：https://stackoverflow.com/questions/4649792/how-concerned-should-we-be-about-thread-safety-with-jsf-managed-beans