Spring Security
the SecurityContextPersistenceFilter is included in the chain to make sure that the SecurityContextHolder is cleared after each request.
Note In an application which receives concurrent requests in a single session, the same SecurityContext instance will be shared between threads. Even though a ThreadLocal is being used, it is the same instance that is retrieved from the HttpSession for each thread. This has implications if you wish to temporarily change the context under which a thread is running. If you just use SecurityContextHolder.getContext().setAuthentication(anAuthentication), then the Authentication object will change in all concurrent threads which share the same SecurityContext instance. You can customize the behaviour of SecurityContextPersistenceFilter to create a completely new SecurityContext for each request, preventing changes in one thread from affecting another. Alternatively you can create a new instance just at the point where you temporarily change the context. The method SecurityContextHolder.createEmptyContext() always returns a new context instance.
5.5 Access-Control (Authorization) in Spring Security The main interface responsible for making access-control decisions in Spring Security is the AccessDecisionManager. It has a decide method which takes an Authentication object representing the principal requesting access, a “secure object� (see below) and a list of security metadata attributes which apply for the object (such as a list of roles which are required for access to be granted).
Security and AOP Advice If you're familiar with AOP, you'd be aware there are different types of advice available: before, after, throws and around. An around advice is very useful, because an advisor can elect whether or not to proceed with a method invocation, whether or not to modify the response, and whether or not to throw an exception. Spring Security provides an around advice for method invocations as well as web requests. We achieve an around advice for method invocations using Spring's standard AOP support and we achieve an around advice for web requests using a standard Filter. For those not familiar with AOP, the key point to understand is that Spring Security can help you protect method invocations as well as web requests. Most people are interested in securing method invocations on their services layer. This is because the services layer is where most business logic resides in current-generation J2EE applications. If you just need to secure method invocations in the services layer, Spring's standard AOP will be adequate. If you need to secure domain objects directly, you will likely find that AspectJ is worth considering. You can elect to perform method authorization using AspectJ or Spring AOP, or you can elect to perform web request authorization using filters. You can use zero, one, two or three of these approaches together. The mainstream usage pattern is to perform some web request authorization, coupled with some Spring AOP method invocation authorization on the services layer.
3.0.5.RELEASE
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