Synchronizing access to a MDB method across instances

I have an Message Driven Bean, which receives Audit messages. These messages also have information about the system being audited. When a message is received, the MDB can create the system if it does not exists or reuse an existing system.

My challenge is that when a lot of messages from a new system are received simultaneously, multiple MDB instances are created and can end up creating duplicate systems. Adding a constraint to the database is one way to solve it. Is there a way of avoiding these duplicates in the application, MDB in this case?

You could try something like this:

private Object LOCK;
public void onMessage() {
    code…
    synchronized(LOCK) {
        check if system exists, create if necessary
    }
    more code…
}