ClassA.java  
@Transactional  
public void methodA(){          
    ExecutorService executorService = Executors.newFixedThreadPool(4);  
    executorService.execute(new Runnable() {  
        public void run() {  
            classB.methodB();  
        }  
});  
}  
ClassB.java  
@Transactional  
public void methodB(){  
    updateDB();  
}