The Stream API in Java 8 is a blast. Finally, it is possible to easily write concise, declarative code just with pure JDK. There is one problem though - the limitation that lambdas cannot throw checked exceptions. I am sure there are plenty of good reasons not to do such terrible thing, but honestly: it just pisses off. So, I should do something with it then. First attempt is to wrap the lambda's body with a function which would turn the exception from checked to unchecked one (assuming the TechnicalException extends RuntimeException):
public static <T, R> Function<T, R> unchecked(FunctionWithException<T, R> f) { Function<T, R> rf = p -> { try { return f.invokeIt(p); } catch (Exception e) { throw new TechnicalException("Exception within lambda expression:", e); } }; return rf; }
and write something like this:
List<File> filesList = ... filesList.stream() .map( unchecked( file -> FileUtils.readFileToString(file, "UTF-8" ) ) ) .map( .... );
but, it obviously is not working, since the Function
public static <T, R> Function<T, R> unchecked(FunctionWithException<T, R> f) { Function<T, R> rf = p -> { try { return f.invokeIt(p); } catch (Exception e) { throw new TechnicalException("Exception within lambda expression:", e); } }; return rf; }
Unfortunatelly, depending on the later usage, we may need multiple versions for different interfaces from java.util.function, but we can hide this ughliness in some class :)
