Java AppDomain like abstraction?

I think Yiannis's answer here is a little misleading. Simply saying "no, you can't" is not the whole story. The question is focused on unloading Java classes in a server process to remove leaky code from the JVM process without a process restart. The OP is not asking for the process-like memory isolation feature that an AppDomain gives, but the ability to unload classes in a running JVM. I say process-like, since under the hood an AppDomain is not a process, but enjoys some of the isolation aspects that a first-class process is afforded by the operating system. The isolate JSR mentioned is referring to this 'process-like' isolation. Unloading java ClassLoaders and thus classes, without cycling the OS process hosting the JVM is possible. A couple of methods are mentioned here: SO 148681. It is not trivial, or elegant to do this in Java, but it is possible.

Unfortunately, no.

The analogous concept in the Java world is the Isolate, that appeared first in the JSR 121. This was an API for a future JVM feature that would allow safe separation and communication between different applications running in the same JVM. After the JSR was published (around 2004) one research team in Sun worked in the Barcelona project. This project tried to implement the Isolation API in Sun's HotSpot 1.5 VM. After two years, they released a prototype for SPARC/Solaris. Windows/Linux versions were never released due to stability problems.

Recently, SUN has introduced a limited version of the Isolation API to J2ME, focusing of offering "multiple processes" in environments that didn't actively offer them. Recently, we also asked Sun for their status in implementing the Isolate API to standard JVMs and their response was that they plan to release a JVM with limited support. They plan to offer the ability to load/unload Isolates but without the ability to communicate between them.

Also, there has been an old reserach efford to build an Isolates-compatible JVM version, called JanosVM (java 1.1) but I doubt that it can be of any use today.

Hope this helps...