Item 61: Throw exceptions appropriate to the abstraction

1.  Higher layers should catch lower-level exceptions and, in their place, throw exceptions that can be explained in terms of the higher-level abstraction. This idiom is known as exception translation.

 

2.  A special form of exception translation called exception chaining is appropriate in cases where the lower-level exception might be helpful to someone debugging the problem that caused the higher-level exception. The lower-level exception (the cause) is passed to the higher-level exception, which provides an accessor method (Throwable.getCause) to retrieve the lower-level exception. Most standard exceptions have chaining-aware constructors. For exceptions that don’t, you can set the cause using Throwable’s initCause method. Not only does exception chaining let you access the cause programmatically (with getCause), but it integrates the cause’s stack trace into that of the higher-level exception.

 

3.  Where possible, the best way to deal with exceptions from lower layers is to avoid them, by ensuring that lower-level methods succeed. Sometimes you can do this by checking the validity of the higher-level method’s parameters before passing them on to lower layers. If it is impossible to prevent exceptions from lower layers, the next best thing is to have the higher layer silently work around these exceptions, insulating the caller of the higher-level method from lower-level problems. Under these circumstances, it may be appropriate to log the exception using some appropriate logging facility such as java.util.logging. This allows an administrator to investigate the problem, while insulating the client code and the end user from it.