Emmanuel Bernard wrote: You should in addition to things such as: Thread.currentThread().getContextClassLoader System.getProperty System.setProperty I would not bother to do the SM != null check. The modern jvms are smart enough to do that themselves and speed up. if there is no security mgr enabled, then not much of a difference as the jvm does do some optimization (in the absence of SM). With SM enabled, there is some overhead in the permission checking across call stacks. The JBossAS testsuite includes a test target that runs a bunch of tests while the AS is running under a sec mgr. There are users of AS who run it under a SM.