Question

I am building an update system in which I need to be able to replace a referenced jar of a running application jar at runtime. However, I am running into file locking issues on Windows when trying to perform file utility functions on the jar such as ‘setLastModified’.

After some googling I found this snippet…

What I found in my research is that
the standard ClassLoader
implementation never closes a jar
file once it has been opened. It also
only loads resources from the jar file
as needed. So at any particular time,
there may be Classes in the jar file
that have not been loaded into memory.
Obviously, if you delete the jar file
out from under the ClassLoader, and it
tries to find a resource in the
missing file, you’re going to get an
IOException at the very least.

Does anyone have any references to information on doing this, or working around this issue?

Thanks.

Answer 1

There is a lot of solutions for classes/lib hot-swapping :

• Hotswap for ant
• JRebel
• OSGi

It depends on what you want to do.