How to apply multiple Filters on Java Stream?

Question

I have to filter a Collection of Objects by a Map, which holds key value pairs of the Objects field names and field values. I am trying to apply all filters by stream().filt

Answer 1

A more general approach is to create a multi filter (Predicate) which is concatenated using Predicate.and(...) or Predicate.or(...). This is applicable to anything using Predicate - first of all Stream and Optional.
Since the result is a Predicate itself one can continue with Predicate.and(...) or Predicate.or(...) or with building more complex predicates using MultiPredicate again.

class MultiPredicate {

    public static  Predicate matchingAll(Collection> predicates) {
        Predicate multiPredicate = to -> true;
        for (Predicate predicate : predicates) {
            multiPredicate = multiPredicate.and(predicate);
        }

        return multiPredicate;    
    }

    @SafeVarargs
    public static  Predicate matchingAll(Predicate first, Predicate... other) {
        if (other == null || other.length == 0) {
            return first;
        }

        Predicate multiPredicate = first;
        for (Predicate predicate : other) {
            multiPredicate = multiPredicate.and(predicate);
        }

        return multiPredicate;
    }

    public static  Predicate matchingAny(Collection> predicates) {
        Predicate multiPredicate = to -> false;
        for (Predicate predicate : predicates) {
            multiPredicate = multiPredicate.or(predicate);
        }

        return multiPredicate;    
    }

    @SafeVarargs
    public static  Predicate matchingAny(Predicate first, Predicate... other) {
        if (other == null || other.length == 0) {
            return first;
        }

        Predicate multiPredicate = first;
        for (Predicate predicate : other) {
            multiPredicate = multiPredicate.or(predicate);
        }

        return multiPredicate;
    }

}

Applying to the question:

public static void main(String... args) {
    List list = new ArrayList<>();
    Map filterMap = new HashMap<>();
    list.add(new TestObject(1, 2, 3));
    list.add(new TestObject(1, 2, 4));
    list.add(new TestObject(1, 4, 3));
    filterMap.put(3, 3); // Filter property3 == 3
    filterMap.put(2, 2); // Filter property2 == 2

    List> filters = filterMap.entrySet().stream()
            .map(filterMapEntry -> mapToFilter(filterMapEntry))
            .collect(Collectors.toList());

    Predicate multiFilter = MultiPredicate.matchingAll(filters);
    List filtered = list.stream()
            .filter(multiFilter)
            .collect(Collectors.toList());
    for (TestObject to : filtered) {
        System.out.println("(" + to.getProperty(1) + "|" + to.getProperty(2) + "|" + to.getProperty(3) + ")");
    }

}

private static Predicate mapToFilter(Entry filterMapEntry) {
    return to -> to.getProperty(filterMapEntry.getKey()) ==  filterMapEntry.getValue();
}

In this case all filters have to match. The result is:

(1|2|3)  

If we use MultiPredicate.matchingAny(...) the result is:

(1|2|3)  
(1|2|4)  
(1|4|3)