@SneakyThrows
can be used to sneakily throw checked exceptions without actually declaring this in your method's throws
clause. This somewhat contentious ability should be used carefully, of course. The code generated by lombok will not ignore, wrap, replace,
or otherwise modify the thrown checked exception; it simply fakes out the compiler. On the JVM (class file) level, all exceptions, checked or not,
can be thrown regardless of the throws
clause of your methods, which is why this works.
Common use cases for when you want to opt out of the checked exception mechanism center around 2 situations:
Runnable
- whatever exception propagates out of your run()
method,
checked or not, it will be passed to the Thread
's unhandled exception handler. Catching a checked exception and wrapping it
in some sort of RuntimeException
is only obscuring the real cause of the issue.new String(someByteArray, "UTF-8");
declares that it can throw an
UnsupportedEncodingException
but according to the JVM specification, UTF-8 must always be available. An
UnsupportedEncodingException
here is about as likely as a ClassNotFoundError
when you use a String object,
and you don't catch those either!
Be aware that it is impossible to catch sneakily thrown checked types directly, as javac will not let you write a catch block
for an exception type that no method call in the try body declares as thrown. This problem is not relevant in either of the use cases listed
above, so let this serve as a warning that you should not use the @SneakyThrows
mechanism without some deliberation!
You can pass any number of exceptions to the @SneakyThrows
annotation. If you pass no exceptions, you may throw any
exception sneakily.
NOTE: with lombok versions older than 0.10, unlike other lombok transformations, you need to put lombok.jar on your classpath when you run your program.
@SneakyThrows
is an implementation of this feature request: http://bugs.sun.com/view_bug.do?bug_id=6534270.
Because @SneakyThrows
is an implementation detail and not part of your method signature, it is an error if you try to
declare a checked exception as sneakily thrown when you don't call any methods that throw this exception. (Doing so is perfectly legal
for throws
statements to accommodate subclasses). Similarly, @SneakyThrows
does not inherit.
For the nay-sayers in the crowd: Out of the box, Eclipse will offer a 'quick-fix' for uncaught exceptions that wraps the offending
statement in a try/catch block with just e.printStackTrace()
in the catch block. This is so spectacularly non-productive
compared to just sneakily throwing the exception onwards, that Roel and Reinier feel more than justified in claiming that the
checked exception system is far from perfect, and thus an opt-out mechanism is warranted.
If you put @SneakyThrows
on a constructor, any call to a sibling or super constructor is excluded from the @SneakyThrows
treatment. This is a
java restriction we cannot work around: Calls to sibling/super constructors MUST be the first statement in the constructor; they cannot be placed inside try/catch blocks.
@SneakyThrows
on an empty method, or a constructor that is empty or only has a call to a sibling / super constructor results in no try/catch block and a warning.