Core Java™ Data Objects

3.10. Exception Handling

All the examples so far have ignored the possibility of exceptions. JDO defines a set of exceptions that can be thrown by the JDO implementation. All JDO exceptions are declared as runtime exceptions because they can be thrown at anytime, not just when calling JDO methods. As an example, navigating from one instance to another may result in an exception if there is a problem with accessing the datastore when retrieving the fields of an instance.

JDO classifies exceptions broadly into fatal or non-fatal exceptions. Non-fatal exceptions indicate that an operation failed but can be retried, whereas fatal exceptions indicate that the only recourse is to start again. Beyond this, there are user exceptions (fatal or non-fatal), ...