Is it possible to add logging to removeIf in java 8?

collections, java, java-8, java-stream

Solution

If this is a recurring problem, you may create a helper method generalizing the task of decorating a predicate with another action, e.g. logging:

static <T> Predicate<T> logging(Predicate<T> p, BiConsumer<T,Boolean> log, boolean all) {
    return t -> {
        final boolean result = p.test(t);
        if(all || result) log.accept(t, result);
        return result;
    };
}

which you may use like

public void testMethod(List<String> prop1, EmailJson randomModel){
    prop1.forEach(s -> randomModel.getSomeList()
        .removeIf(logging(model -> model.getSomeProp().equalsIgnoreCase(s),
            (model,b) -> LOGGER.info(() -> "matched: "+model.getSomeProp()), false)));
}

though, in this specific case, it might be unnecessary to decorate the predicate itself, as `removeIf` return a `boolean` telling whether there were matches to remove, and the match value is still in scope:

public void testMethod(List<String> prop1, EmailJson randomModel){
    prop1.stream().forEach(s -> {
        if(randomModel.getSomeList()
                      .removeIf(model -> model.getSomeProp().equalsIgnoreCase(s)))
            LOGGER.info(() -> "there were matches of: "+s);
    });
}

Problem

Original source