i have java bean like

class OrderDeatils {
    Long orderId;
    Long userId;
    OrderInfo info;

    \\Required getter/setter
}

class OrderInfo {
    OffsetDateTime orderCreatedDate;
    
     \\Required getter/setter
}

I have Data as List<OrderDeatils> list

orderId.   userId.  OrderInfo[orderCreatedDate]. 
1001.       123.      2015/07/07 
1002.       124.      2015/08/07 
1003.       125.      2015/09/07 
1004.       123.      2015/08/07 

How, I can remove duplicate entry based on userId and keep data with min date as below:

orderId.   userId.  OrderInfo[orderCreatedDate]. 
1001.       123.      2015/07/07 
1002.       124.      2015/08/07 
1003.       125.      2015/09/07 

Should return a list of whole OrderDeatils object.

I tried like:

 list.stream().collect(
                Collectors.groupingBy(OrderDeatils::getUserId,
                        Collectors.collectingAndThen(
                                Collectors.reducing((OrderDeatils d1, OrderDeatils d2)
                                        -> d1.getInfo.getOrderCreatedDate().isBefore(d2.getInfo.getOrderCreatedDate()) ? d1 : d2), Optional::get)));

But the response is not as expected, I am not getting updated List<OrderDeatils> as output.

CodePudding user response：

I will not write the code for you, but here are the steps:

• you need a Collectors::toMap that can do a "merge" in the third argument. Something like:

...collect(Collectors.toMap(
     OrderDeatils::getUserId,
     Function.identity(),
     (left, right) ->
        left.getInfo.getOrderCreatedDate().isBefore(right.getInfo.getOrderCreatedDate()) ? left : right        
))

• That will give you a Map<Long, OrderDeatils> from which you need values only.

CodePudding user response：

You can use a simple set to do your filtering. Upon adding to the set - the .add() method will return true if it is a new value and false if the value already exists in the set.

For the sorting, you can use .sorted() and pass a comparator to sort by the wanted field.

Set<String> userIdsSet = new HashSet<>();
List<OrderDetails> filteredOrderDetails = list.stream()
            .filter(e -> userIdsSet.add(e.getUserId()))
            .sorted(Comparator.comparing(OrderDetails::getOrderCreatedDate()))
            .collect(Collectors.toList());