I am new to POI and started learning it. I was able to create an excel sheet using Apache POI 3.6. Now I want to show a prompt box to the user when invalid data is entered into any of the cell. This should happen every time the user is trying to save the data. I need to do it using the functionalities present in POI 3.6. I did a small research for the sample code but was not successful. Can anyone please help me.