How to collect filtered stream array output as list

Question

I am new to Java8 syntax, How can we get the output as list after filtered. In my case filter returns an array.

Added in comments, is there any better way can we get it

Config config = new Config("ooo", "wc", "code");
    Config config1 = new Config("ppp", "wc", "code");
    Config config2 = new Config("ooo", "wc", "code");

    Config[] configs = {config, config1, config2};

    Config config4 = new Config("ooo", "REG", "code");
    Config config5 = new Config("ppp", "REG", "code");
    Config config6 = new Config("ooo", "REG", "code");

    Config[] _configs = {config4, config5, config6};

    PromoCode promoCode = new PromoCode(121, "VOUCHER", "121", configs);
    PromoCode promoCode1 = new PromoCode(122, "VOUCHER", "122", null);
    PromoCode promoCode2 = new PromoCode(123, "LINK", "123", configs);
    PromoCode promoCode3 = new PromoCode(124, "VOUCHER", "124", null);
    PromoCode promoCode4 = new PromoCode(125, "LINK", "125", _configs);
    PromoCode promoCode5 = new PromoCode(126, "LINK", "126", _configs);

    List<String> resultantValues = new ArrayList<String>();
    PromoCode[] promoCodes = {promoCode, promoCode1, promoCode2, promoCode3, promoCode4, promoCode5};
    Stream<PromoCode> stream = Stream.of(promoCodes);
    stream.parallel()
        .filter(x -> x.getCode().equalsIgnoreCase("VOUCHER"))
        .collect(Collectors.toList())
        .parallelStream()
        .forEach(x-> {
            Stream.of(x.getConfigs())
                .filter(t -> t.getOccasion().equals("wc"))
            //after filter, how can we get the output
             // List of list of strings format
                .forEach(o -> {
                    resultantValues.add(o.getProduct()+"_"+o.getProduct());
                });
        });

    System.out.println(resultantValues);

Lino · Accepted Answer · 2018-06-14 12:29:46Z

to retrieve a List<List<T>> it can be done as follows:

 Stream.of(promoCodes)
       .parallel() // is this really needed?
       .filter(x -> x.getCode().equalsIgnoreCase("VOUCHER"))          
       .map(x-> 
            Stream.of(x.getConfigs())
                .filter(t -> t.getOccasion().equals("wc"))
                .map(o ->  o.getProduct()+"_"+o.getProduct())
                .collect(Collectors.toList())
       )
       .collect(Collectors.toList());

or if you want a List<T> format then use flatMap:

 Stream.of(promoCodes)
       .parallel() // is this really needed?
       .filter(x -> x.getCode().equalsIgnoreCase("VOUCHER"))          
       .flatMap(x-> 
            Stream.of(x.getConfigs())
                  .filter(t -> t.getOccasion().equals("wc"))
                  .map(o ->  o.getProduct()+"_"+o.getProduct())
        )
        .collect(Collectors.toList());

or as @Holger mentions, for the second approach you can avoid the nesting in the flatMap with:

 Stream.of(promoCodes)
       .parallel() // is this really needed?
       .filter(x -> x.getCode().equalsIgnoreCase("VOUCHER"))
       .flatMap(x -> Arrays.stream(x.getConfigs()))
       .map(x -> x.getProduct() + "_" + x.getProduct())
       .collect(Collectors.toList());

Which is definitely more readable:

Note that I've also removed some of the unnecessary method calls such as the intermediate collecting to a list .collect(Collectors.toList()) , .parallelStream() et al.

Ravindra Ranwala · Accepted Answer · 2018-06-14 17:28:59Z

0

This should give you the desired results. First filter the promocodes with the given code VOUCHER. For each filtered promocode, you have an array of configs. We get that and flatten it to get a stream of Config objects. In the next step we filter out all the configs whose occasion is not equal to wc. Then we map all the matching config objects to get the desired result. At the final step we collect the result into a container.

final List<String> finalResult = Stream.of(promoCodes)
        .filter(pc -> pc.getCode().equalsIgnoreCase("VOUCHER"))
        .flatMap(pc -> Stream.of(pc.getConfigs()))
        .filter(conf -> conf.getOccasion().equals("wc"))
        .map(conf -> conf.getProduct() + "_" + conf.getProduct())
        .collect(Collectors.toList());

edited Jun 14, 2018 at 17:28

answered Jun 14, 2018 at 17:23

Ravindra Ranwala

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