Sometimes we need to create custom Exception in Java, i.e. Exceptions which are not defined in JDK or any third party library your application is using. Though it’s widely recommended on several Exception best practices article, even Joshua Bloch has recommended in Effective Java to prefer standard exception over custom exception, sometimes you really need it. There are certain guidelines to help to find whether you really need a custom exception or not. You should write your own exception classes if you answer yes to any of the following questions; otherwise, you can probably use someone else's.
- Do you need an exception type that isn't represented by those in the Java platform?
- Would it help users if they could differentiate your exceptions from those thrown by classes written by other vendors?
- Does your code throw more than one related exception?
- If you use someone else's exceptions, will users have access to those exceptions? The similar question is, should your package be independent and self-contained?