How to handle exceptions in lambda expressions [duplicate]

Question

I have metohod MyService#create which throws CustomException. I call this method in Optional#map like below:

return Optional.ofNullable(obj)
        .map(optObj -> {
            try {
                return myService.create(optObj);
            } catch (CustomException e) {
                return new ResponseEntity<>(e.getMessage(), HttpStatus.BAD_REQUEST);
            }
        })
        .map(created -> new ResponseEntity<>("Operation successful", HttpStatus.CREATED))
        .orElse(new ResponseEntity<>("Operation failed", HttpStatus.BAD_REQUEST));

And when I call this method with arguments which cause exception then CustomException is catched but in result I get Operation successful and status 200. How to handle this exception in lambda and return message from exception?

No, there is throwing exception in lambda. I want to catch and return right result — user
– user, Commented Jul 27, 2017 at 11:16
What is the reason behind using Optional at all? A simple if - then - else is enough here, maybe in companion with a try - catch. — Seelenvirtuose
– Seelenvirtuose, Commented Jul 27, 2017 at 11:16
try using wrapper method that will be responsible for handling the exception — sForSujit
– sForSujit, Commented Jul 27, 2017 at 11:17

talex · Accepted Answer · 2017-07-27 11:24:08Z

2

You do catch exception and return new ResponseEntity<>(e.getMessage(), HttpStatus.BAD_REQUEST).

Then you map it to new ResponseEntity<>("Operation successful", HttpStatus.CREATED).

If you want to have new ResponseEntity<>("Operation successful", HttpStatus.CREATED) only if call is successful rewrite your code to:

return Optional.ofNullable(obj)
        .map(optObj -> {
            try {
                myService.create(optObj);
                return new ResponseEntity<>("Operation successful", HttpStatus.CREATED);
            } catch (CustomException e) {
                return new ResponseEntity<>(e.getMessage(), HttpStatus.BAD_REQUEST);
            }
        })
        .orElse(new ResponseEntity<>("Operation failed", HttpStatus.BAD_REQUEST));

answered Jul 27, 2017 at 11:24

talex

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