Java: How to atomically replace all values in a Map?

Question

I have a stateful bean in an multi-threaded enviroment, which keeps its state in a map. Now I need a way to replace all values of that map in one atomic action.

Answer 1

Since the map is quite small, it's probably enough to just use synchronized in all places you access it.

private void atomicallyUpdateState(final Map newState) {
    synchronized(state) {
        state.clear();
        state.putAll(newState);
    }
}

but don't forget any, like all occurances of things like

String myStatevalue = state.get("myValue");

need to become

String myStatevalue;
synchronized (state) {
    myStatevalue = state.get("myValue");
}

otherwise the read and update are not synchronized and cause a race condition.