Java 嵌套过滤器和嵌套流

Question

class Item {
  int id;
  List<PriceDetails> priceDetails;
  String itemName;
}

---

class PriceDetails {
  int price;
}

I am getting multiple items in a JSON file. I am trying to filter priceDetails with empty price (not the items, just removing all the priceDetails in the list with empty price)

I am able to write Java code and its working as expected, but I don't know how to write using Java Streams. Can someone help me?

Thanks in advance.

Java Code:

public static List<Item>  filterByEmptyPrice(List<Item> items) {
    List<Item> result= new ArrayList<>();
    for(int i=0;i<items.size();i++) {
        List<PriceDetails> temp= new ArrayList<>();
        for(int j=0;j<items.get(i).PriceDetails.size();j++) {
            if(nonNull(items.get(i).PriceDetails) && nonNull(items.get(i).priceDetails.get(j).priceDetails.price)) {
                temp.add(items.get(i).priceDetails.get(j));
            }
        }
        items.get(i).priceDetails= temp;
        result.add(items.get(i));
    }
    return result;
}

Answer 1

Your filterByEmptyTicketPrice() method doesn't compile with the Item and PriceDetails model you gave.

The correct loop based implementation would be:

    public static List<Item> filterByEmptyTicketPrice(List<Item> items) {
        List<Item> result = new ArrayList<>();
        for (Item item : items) {
            List<PriceDetails> temp = new ArrayList<>();
            for (PriceDetails priceDetails : item.priceDetails) {
                if (nonNull(priceDetails.price)) {
                    temp.add(priceDetails);
                }
            }
            // bug: you mutate your method input here
            item.priceDetails = temp;
            result.add(item);
        }
        return result;
    }

Also, as noted above, you're mutating the input items . The correct way to do this with streams and without mutating the input would be:

    public static List<Item> filterByEmptyTicketPrice(List<Item> items) {
        return items.stream()
                .map(item -> new Item(filterPrices(item.priceDetails)))
                .collect(Collectors.toList());
    }

    static List<PriceDetails> filterPrices(List<PriceDetails> priceDetailsList) {
        return priceDetailsList
                .stream()
                .filter(priceDetails -> priceDetails.price != null)
                .collect(Collectors.toList());
    }

This example assumes you've added a new Item constructor such as:

public Item(List<PriceDetails> priceDetails) {
    this.priceDetails = priceDetails;
}

As others mentioned, you should update the model to use getters to access priceDetails and price making them private in your Item and PriceDetails classes.