How to create reusable optional mapping with method references?

cmlonder :

While I'm trying to use Optional features with method references, it really confused me how to optimize it with reusable code. I think I'm stuck while trying to use all those new features (for me) at the same time i decided to get rid of java-6 style, now I think i can't think simple, i feel that it gets overcomplicated. How can i create

List<BooleanExpression> expressionMapping = new ArrayList<>();

    if (request != null) { // request is input parameter, a DTO

        Optional.ofNullable(request.getPlantId())
            .map(campaign.plant.id::contains) // campaign is static created by Querydsl
            .ifPresent(expressionMapping::add);

        Optional.ofNullable(request.getTitle())
            .map(campaign.title::containsIgnoreCase)
            .ifPresent(expressionMapping::add);

        Optional.ofNullable(request.getCampaignNumber())
            .map(this::getLikeWrapped)
            .map(campaign.campaignNumber::like)
            .ifPresent(expressionMapping::add);
... 20 more Optional bunch of code like this
}

also having trouble with writing this code with Optional like previous ones:

if (request.getLockVehicle() != null) {
            if (request.getLockVehicle()) {
                expressionMapping.add(campaign.lockVehicle.isNotNull());
            } else {
                expressionMapping.add(campaign.lockVehicle.isNull());
            }
        }

oleg.cherednik :

What about use enum to declare all fields from Request and use it as common part of the code. I did not check it, this is only to show my approach:

public enum RequestField {
    PLANT_ID(Request::getPlantId, (val, campaign) -> campaign.plant.id::contains),
    TITLE(Request::getTitle, (val, campaign) -> campaign.title::containsIgnoreCase),
    CAMPAIGN_NUMBER(Request::getCampaignNumber, (val, campaign) -> campaign.campaignNumber::like),
    // ... more fields here ...
    ;

    private final Function<Request, Optional<Object>> get;
    private final BiFunction<Object, Campaign, BooleanExpression> map;

    RequestField(Function<Request, Object> get, BiFunction<Object, Campaign, BooleanExpression> map) {
        this.get = get.andThen(Optional::ofNullable);
        this.map = map;
    }

    public static List<BooleanExpression> getBooleanExpressions(Request request, Campaign campaign) {
        if (request == null)
            return Collections.emptyList();

        List<BooleanExpression> res = new LinkedList<>();

        for (RequestField field : values())
            field.get.apply(request)
                     .map(r -> field.map.apply(r, campaign))
                     .ifPresent(res::add);

        return res.isEmpty() ? Collections.emptyList() : Collections.unmodifiableList(res);
    }
}

And your client code will be looking like:

List<BooleanExpression> booleanExpressions = RequestField.getBooleanExpressions(request, campaign);

P.S. Your last code could be look like:

if (request.getLockVehicle() != null)
    expressionMapping.add(request.getLockVehicle() ? campaign.lockVehicle.isNotNull() : campaign.lockVehicle.isNull());