Filter Map

This Java library adds a stream gatherer operation which maps one value to another and only includes the output if it is not null.

Install

FilterMap is uploaded to Maven Central. Instructions for your specific build tool are there.

implementation 'dev.piggle:FilterMap:<release>'

How to use

Below is a comparison between filter map behaviour with and without FilterMap. The FilterMap class contains static methods with some common mappers for instanceof and optionals.

import dev.piggle.filtermap.FilterMap;

void example() {
    // Without filter map
    List<?> mapFilter = Stream.of(...)
        .map(mapper)
        .filter(Objects::nonNull)
        .toList();

    // With filter map
    List<?> filterMap = Stream.of(...)
        .gather(FilterMap.of(mapper)) // Same mapper as before
        .toList();
    
    List<Integer> integers = Stream.of(1, 2, 3.0) // Cheeky double
            .gather(FilterMap.filterInstanceOf(Integer.class)) // Only keeps the integers
            // This is now a stream of integers due to the filter map above
            .toList();
}

There should be negligible difference in performance between these two methods of mapping and filtering (unconfirmed), so whether you use FilterMap or not is mostly down to personal preference.