Conditioning the filters of a java stream

Question

i'm working on a filter function that can filter with many parameters and to do that i'm using Java Streams. So that is my code :

public void filter(String cours,String prof,String salle,String group) {

this.appointments().addAll(getTimeTable().getCreneauxsList().stream()
            .filter(e->e.getProf().equalsIgnoreCase(prof) )
            .filter(e->e.getCours().equalsIgnoreCase(cours) )
            .filter(e->e.getSalle().equalsIgnoreCase(salle) )
            .filter(e->e.getGroup().equalsIgnoreCase(group) )
            .collect(Collectors.toList()));
}

I want to see if one or many the parameters cours,salle,prof,group are null or its trim () = "", it's not worth it to filter with it cause the result is not what i expected to get.

But I do not know how to do it.

In my collection there are some fields that are null so if one of the parameters is null i got these fields but i want if the parameter is null or its trim()="" so there is no filter — Salif Ano, Feb 17 '19 at 09:29
something like `e -> StringUtils.isBlank(prof) || e.getProf().equalsIgnoreCase(prof)` — Wisthler, Feb 17 '19 at 09:31
So, you wanna get the list of objects whose fields are null or empty strings — uneq95, Feb 17 '19 at 09:31
no, the filter to be applied only if the criteria is not blank — Wisthler, Feb 17 '19 at 09:32
@Wisthler yes that's what i want to do, does StringUtils alreary exist in java? — Salif Ano, Feb 17 '19 at 09:35
StringUtils is part of Apache Commons-Lang: https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html — Wisthler, Feb 17 '19 at 09:38

score 2 · Accepted Answer · answered Feb 17 '19 at 09:36

You can create a method to handle the null or empty string during filter like below:

public static boolean compareNullableString(String str, String filterStr) {

    return (filterStr == null || filterStr.trim().equals("")) ? true : filterStr.equalsIgnoreCase(str);

}

And then modify your code like:

this.appointments().addAll(getTimeTable().getCreneauxsList().stream()
                .filter(e->compareNullableString(e.getProf,prof) )
                .filter(e->compareNullableString(e.getCours,cours))
                .filter(e->compareNullableString(e.getSalle,salle) )
                .filter(e->compareNullableString(e.getGroup,group) )
                .collect(Collectors.toList()));

Maybe it's just me, but `return filterStr == null || filterStr.trim().isEmpty() || filterStr.equalsIgnoreCase(str);` seems more readable — ernest_k, Feb 17 '19 at 09:40
@ernest_k You are right. That's a good suggestion. It will make the statement brief and more readable. Thanks!!! — Amit Bera, Feb 17 '19 at 09:43

Ruslan · Answer 2 · 2019-02-17T10:08:52.977

You can use Strings.isNullOrEmpty() from guava:

boolean isNullOrEmpty = Strings.isNullOrEmpty(e.getProf());

Or there is a set of methods from apache commons:

StringUtils.isBlank, StringUtils.isNotBlank, StringUtils.isEmpty, StringUtils.isNotEmpty

This might be useful: StringUtils.isBlank() vs String.isEmpty()

It your case isNotBlank exactly what you are looking for:

BiPredicate<String, String> myPredicate = (field, eqString) ->
        StringUtils.isNotBlank(field) && field.equalsIgnoreCase(eqString);

    ...
    .filter(e -> myPredicate.test(e.getProf(), prof))
    .filter(e -> myPredicate.test(e.getCours(), cours))
    .filter(e -> myPredicate.test(e.getSalle(), salle))
    .filter(e -> myPredicate.test(e.getGroup(), group))
    ...

lczapski · Answer 3 · 2019-12-30T09:43:32.333

This answer can be improved.

Method compareNullableString can be as it is. You can get rid of creating List and adding element in forEach. Filtering can be also extracted to Predicate.

List<String> appointments = this.appointments();

Stream<Predicate<Creneauxs>> filterStream = Stream.of(
        e->compareNullableString(e.getProf,prof),
        e->compareNullableString(e.getCours,cours),
        e->compareNullableString(e.getSalle,salle),
        e->compareNullableString(e.getGroup,group)
);
Predicate<Creneauxs> filter = filterStream.reduce(Predicate::and).orElse(x->false);

getTimeTable().getCreneauxsList().stream()
  .filter(filter)
  .forEach(appointments::add);

Conditioning the filters of a java stream

3 Answers3