Java 8 - stream - method in filter has unhandled exception, try catch is expecting return statement

Question

I am using a function call is filter on a stream like below -

list.stream()
        .filter(a -> !StringUtils.isEmpty(a.getProp1()))
        .filter(a -> !a.getProp1().matches(“(.*)xyz"))
        .filter(a -> {try {
                        return isValid(a.getProp1());
                    } catch (javax.naming.NamingException e) {
                        logger.error("Error");
                    }
                    })

I referred to the question But I don't want to throw an exception in the catch block. I just want to log it.

I want to retain the records which return true on invoking isValid(a) and then be able to collect it in a HashSet like below --

 //   .collect(Collectors.toCollection(HashSet::new));

It must be obvious from code but I am new to java 8 and still learning concepts. Please pardon any naive code. Thanks for any help.

in the 3rd filter, when you catch your exception, should be the "a" filtered out or not? Not missing a "return false" or sth like that? — fairtrax, Jul 19 '17 at 17:01

fps · Accepted Answer · 2017-07-19T17:11:57.857

2

As you are filtering, if the isValid method throws a javax.naming.NamingException, apart from logging the exception, you might want to return false:

Set<Whatever> result = list.stream()
    .filter(a -> !StringUtils.isEmpty(a.getProp1()))
    .filter(a -> !a.getProp1().matches("(.*)xyz"))
    .filter(a -> {
        try {
            return isValid(a.getProp1());
        } catch (javax.naming.NamingException e) {
            logger.error("Error");
            return false;
        }})
    .collect(Collectors.toCollection(HashSet::new));

This is because the Predicate argument passed to the Stream.filter method must always return a boolean value, no matter if it has catched an exception or not.

edited Jul 19 '17 at 17:11

answered Jul 19 '17 at 17:00

fps

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That makes sense, even after adding a `return false`, I am not able to collect the list which is an arraylist into a hashSet. I get a compilation error saying 'Bad return type in method reference. – maddie Jul 19 '17 at 17:05
`Set mySet = new HashSet<>(); mySet = list.stream() .filter(a -> !StringUtils.isEmpty(a.getProp1())) .filter(a -> !a.getProp1().matches(“(.*xyz”)) .filter(a -> {try { return isValid(a.getProp1()); } catch (javax.naming.NamingException e) { logger.error("Error"); return false; } }) .collect(Collectors.toCollection(HashSet::new));` This is my final code. – maddie Jul 19 '17 at 17:05
@maddie Please check if it works after my last edit. The other strange thing I notice is the use of typographic quotes in the second `filter(...)`... – fps Jul 19 '17 at 17:06
@maddie The other problem is the `Set mySet`. Is it really a set of strings? I think it's a set of some object of yours, while `getProp1()` returns an actual string. – fps Jul 19 '17 at 17:10
1

Yes, you guessed it right, I will fix it. I guess I will reassign the modified list to list itself in that case. Thanks so much. – maddie Jul 19 '17 at 17:12
@maddie So you only want to remove elements from the original list? – fps Jul 19 '17 at 17:14
1

I actually added a `.map(a -> a.getProp1())` after all the filters. i am able to collect it as a HashSet. Thanks! – maddie Jul 19 '17 at 17:14
@maddie OK, that makes sense. Cheers! – fps Jul 19 '17 at 17:15
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/149639/discussion-between-federico-peralta-schaffner-and-maddie). – fps Jul 19 '17 at 17:15

Java 8 - stream - method in filter has unhandled exception, try catch is expecting return statement

1 Answers1