How to apply a collection of filters to a Java stream?

user_131021 0
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How can I apply a collection of predicates to a Java stream?

The following code shall illustrate what I have in mind:

final Collection<Predicate<MyObject>> filters = getFilters();
final Stream<MyObject> oStream = getMyObjectStream();
oStream
   .filterAll(filters) // <- this one doesn't exist
   .forEach(System.out::println);

I'm currently using a function .filter(m -> applyAllFilters(m, filters)) with a classic loop, but wonder if there is a more "streamy" way?

boolean applyAllFilters(final MyObject m, final Collection<Predicate<MyObject>> filters) {
   Iterator Predicate<MyObject> iter = filters.iterator();
   while(iter.hasNext()) {
      Predicate<MyObject> p = iter.next();
      if (!p.test(m)) {
         return false;
      }
   } 
  return true;
}
java-stream java-8 java
3 Answers

You can simply reduce all the predicates into one single Predicate that is anded with all of them like this:

oStream
    .filter(filters.stream().reduce(Predicate::and).orElseThrow())
    .forEach(System.out::println);

Alternatively, if you expect the list of filters to be empty in some cases, you could do it this way:

oStream
    .filter(filters.stream().reduce(o -> true, Predicate::and))
    .forEach(System.out::println);
user_36459440

You can pre-create a filter that meet all the criteria.

Suppose you have three Predicate <MyObject> a, b, c. These can be combined as follows regardless of oStream.

Predicate<MyObject> allFilter = e -> a.test(e) && b.test(e) && c.test(e);

So you can do like this.

Predicate<MyObject> filterAll = filters.stream()
    .reduce(Predicate::and).orElse(e -> true);

oStream
   .filter(filterAll)
   .forEach(System.out::println);
Admin1

You can use a loop to apply the filters:

final Collection<Predicate<MyObject>> filters = getFilters();

Stream<MyObject> oStream = getMyObjectStream();
for(Predicate<MyObject> p : filters) {
    oStream = oStream.filter(p);
}
oStream.forEach(System.out::println);
user_122990000
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