When developing an application, we often spend most of the time on the passing code path, as the code path gives the application its actual feature. However, it is important to not forget all the unexpected cases. It can sound weird to try to solve something we don't control but, here, the idea is to follow the Murphy's law which is often summarized as follows: anything that can go wrong, will go wrong. It doesn't mean that the system will never work, but it means that if there is a potential issue, it will become your reality one day or another.
In terms of a modern system and, more particularly, Java EE deployment, the typical consequence is that you can lose the connectivity to a related resource or application. Another common failure case you can desire to address is about the JVM failing (no more memory, OS issue, and so on), but this...