How can I log a value in a Java Optional.of chain? [duplicate]

Question

I'm using an Optional.of chain in Java to get a value,

Integer yearOfBirth = Optional.ofNullable(employee)
                              .map(Employee::getDateOfBirth)
                              .map(LocalDateTime::getYear())
                              .orElseThrow(new EmployeeException("Date of birth not set for {}", employee));

Is it possible to insert a log statement in the chain so that the date of birth is logged, without being consumed by the chain itself?

If you want to convert to a Stream, you may use its peek method, but it’s probably not worth it. You would need to go .stream() .peek(...) ... .findAny() .orElseThrow(...). — Anonymous
– Anonymous, Commented Jan 21 at 16:42
What would be the point of logging from within the call chain in your example? Just do log.info("dob {}", employee.getDateOfBirth()); before creating the Optional? Also, if your chain throws, you know there isn’t a date of birth, and if it doesn’t, you know there is (only you only know the year). — Anonymous
– Anonymous, Commented Jan 21 at 16:45
the employee object can be null, I've updated the code snippet with ofNullable — mccarthyj
– mccarthyj, Commented Jan 21 at 17:08

Mureinik · Accepted Answer · 2025-01-21 16:01:47Z

4

You can replace the getDayOfBirth reference with a lambda that logs it and then returns it:

Integer yearOfBirth = 
    Optional.of(employee)
            .map(e -> {
                   LocalDateTime dob = e.getDateOfBirth();
                   logger.info("Date of Birth is " + dob);
                   return dob;
             })
            .map(LocalDateTime::getYear())
            .orElseThrow(new EmployeeException("Date of birth not set for {}", employee));

answered Jan 21 at 16:01

Mureinik

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3 Comments

mccarthyj Jan 21 at 16:11

thanks, I was hoping for a single line solution, something like .map(Employee::getDateOfBirth) .passThrough(dob -> log.info("Date of Birth: {}", dob)) .map(LocalDate::getYear)

Mureinik Jan 21 at 16:13

@mccarthyj You can always turn this into a method, and then call it in a single line

mccarthyj Jan 21 at 16:15

that might be the simplest solution, thank you

Akshansh Jain · Accepted Answer · 2025-01-21 16:41:54Z

0

If you want to do it at multiple places, with different logics (logs or just any similar side-effect), you might benefit by adding a peek function in a common utility, as described in the below answer

How to peek on an Optional?

answered Jan 21 at 16:41

Akshansh Jain

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