过滤搜索Java 8流

Question

I am trying to write filter function with Java 8 streams to filter by multiple paramaeters.

createdFrom - Date (mm-dd-yyyy) // if null, filter without createddate From
createdTo - Date - (mm-dd-yyyy) // if null, filter without createddate to
CreatedBy - String //if null, filter without createdby
Intaketype - List<String> // if empty, filter with all intaketypes

If any of the parameters is not passed, I do not want to filter by that parameter. For example If I am given createdBy null, intaketype is 'Approved' and createdfrom is 02-04-2017 createdto is 03-03-2018 then i want all approved intakes from the given dates created by all users.

List<Intake> intakes= intakeservice.getAllintakes.stream()
        .filter(el -> intaketype.getIntaketype.contains(el.getIntaketype())
                    && intaketype.getCreatedBy.contains(el.getCreatedBy())
        && el.getCreatedDate().before(el.dateTo)
        && el.getCreatedDate().after(el.dateFrom))
        .collect(Collectors.toList());

My code however,returns an empty array if any of the parameters passed is null or empty. I am not sure how to tell it to not filter by a particular parameters if not passed, empty or null.

Thanks a lot for your help!

Answer 1

I suggest you create multiple .filter(), where you describe logic for one rule. The .filter() rules are with logical AND in the stream, ie if one of the .filter() rules is false, then this will not be processed.

List<Intake> intakes= intakeservice.getAllintakes.stream()
    .filter(el -> Objects.isNull(el.dateTo) || el.getCreatedDate().before(el.dateTo))
    .filter(el -> Objects.isNull(el.dateFrom) || el.getCreatedDate().after(el.dateFrom))
    .filter(el -> Objects.isNull(el.getCreatedBy) || intaketype.getCreatedBy.contains(el.getCreatedBy()))
    .filter(el -> Objects.isNull(el.getIntaketype) || el.getIntaketype.size == 0 || intaketype.getIntaketype.contains(el.getIntaketype())
    .collect(Collectors.toList());

Let's dig into one of the rules: el -> Objects.isNull(el.dateTo) || el.getCreatedDate().before(el.dateTo)

If dateTo is null, then the result of the lambda is true. if dateTo is not null, then result is the comparison of the dateTo with el.getCreatedDate()

If the .filter() is false, then this record will be filtered and not proccessed down the stream.