Is there any way to Stream Map Filter & Map back to original object in Java 8?

Question

Is there any way to Stream the list --> map --> filter --> map back to original object type of list?

There is solution if we are doing it using foreach as below:

List<Query> updatedQueries = getUpdatedQueries();

List<Query> finalQueries = new ArrayList<>();
updatedQueries.forEach(query -> {

    Period period = getPeriodRequest(query);
    boolean isValidPeriod = periodService.validatePeriodicity(period);
    if(isValidPeriod &&  isMandatory(period)){
        finalQueries.add(query);
    }

});

But is there any way to do it using following way ?

List<Query> updatedQueries = getUpdatedQueries();

List<Query> finalQueries = updatedQueries
        .stream()
        .map(this::getPeriodRequest) //returns the object of type Period
        .filter(period->periodService.validatePeriodicity(period))
        .filter(this::isMandatory)
        //is any way we can map back to Query object (without any object translation  function)
        .collect(Collectors.toList());

Answer 1

Try this one

List<Query> finalQueries = updatedQueries
    .stream().filter(query->{
        Period period = getPeriodRequest(query);
        return periodService.validatePeriodicity(period )&& isMandatory(period))
    })
    .collect(Collectors.toList());

Answer 2

You can expand the filter as:

    List<Query> finalQueries = updatedQueries
            .stream()
            .filter(query -> {
                Period period = getPeriodRequest(query);
                return periodService.validatePeriodicity(period) && isMandatory(period);
            })
            .collect(Collectors.toList());

Answer 3

First of all your actual result is of type List<Period> finalQueries because of that map(this::getPeriodRequest). Simply use some "longer" lambdas:

 updatedQueries.stream()
               .filter(q -> periodService.validatePeriodicity(q.getPeriodRequest()))
               .filter(q -> isMandatory(q.getPeriodRequest()))
               .collect(Collectors.toList())

You can even compress those two filters into a single one and read q.getPeriodRequest() only once if you really wanted to.

Or you could map to a SimpleEntry for example:

 updatedQueries.stream()
               .map(x -> new SimpleEntry<>(x, x.getPeriodRequest()))
               .filter(e -> periodService.validatePeriodicity(e.getValue()))
               .filter(e -> isMandatory(e.getValue()))
               .map(Entry::getKey)
               .collect(Collectors.toList());