Java - 如何将旧方式代码块 null 检查切换到可选 null 检查？

Question

Trying to refactor my whole project.

l want this block to be simpler with Optional Java 8 null checks if possible to be the same results at the end? Thanks

List<EntityDto> ventolinLogs = new ArrayList<>();
 for (VentolinLog logs : ventolinLogsList) {
   for (String ventolinId : logs.getVentolinIds()) {

   Ventolin ventolin = persistence.get(Ventolin.class, ventolinId);
   String ventolinName= "";
   String ventolinFirstName= "";

   if (ventolin != null) {
     ventolinName= ventolin.getVentolinName();
     ventolinFirstName= ventolin.getFirstName();
   }

   VentolinProfile ventolinProfile = persistence.get(VentolinProfile.class, ventolinId);
   String ventolinProfileName= "";

   if (ventolinProfile != null) {
     ventolinProfileName= ventolinProfile.getName();
   }

   EntityDto LogDto = EntityDto.builder()
            .ventolinId(ventolinId)
            .ventolinName(ventolinName)
            .ventolinFirstName(ventolinFirstName)
            .ventolin

      ventolinLogs.add(LogDto);
   }
}

Answer 1

Make persistence.get return an Optional. You can use return Optional.ofNullable(result) to do this in your Persistence Class.

In your code use can now use:

Optional<VentolinProfile> ventolinProfile = persistence.get(VentolinProfile.class, ventolinId);
String ventolinProfileName = ventolinProfile.map(VentolinProfile::getName).orElse("");

For more information check out some tutorials on optionals like here: https://www.baeldung.com/java-optional

But as you see, it won't shorten the code very much.

Answer 2

In case you can return an optional from the Persistence class or, like in the example, just create an optional, you can do the following:

ventolinProfileName = Optional.ofNullable(ventolinProfile).map(VentolinProfile::getName).orElse(ventolinProfileName); // or just "" in the last brackets

I would also extract the builder to a variable and pass it to a lambda:

EntityDtoBuilder builder = EntityDto.builder();
Optional.ofNullable(ventolin).ifPresent(vp-> builder.ventolinName(vp.getVentolinName())
.ventolinFirstName(vp.getFirstName()))

But you should take care of the default values, which are initialized as empty strings in your code