Java 8：按多个字段分组，然后根据值排序

Question

I have a class called Info

public class Info {
    private String account;
    private String opportunity;
    private Integer value;
    private String desc;
}

I want to group a list of Info , by two fields(account and then opportunity) and then sort it based on value. ie List of info before grouping and sorting:

List<Info> infos = [(account = 1234, opportunity = abs, value = 4, desc= test),
(account = 1234, opportunity = abs, value = 5, desc = testing),
(account = 1234, opportunity = abss, value = 10, desc = vip),
(account = 123, opportunity = abss, value = 8, desc = vip),
(account = 12, opportunity = absddd, value = 4, desc = production),
(account = 12, opportunity = absooo, value = 2, desc = test)]

The result I expected after grouping and sorting,

Map<String, Map<String, List<Info>>> result = {
    1234 = {
        abss = [(account = 1234, opportunity = abss, value = 10, desc = vip)],
        abs = [(account = 1234, opportunity = abs, value = 5, desc = testing),  
               (account = 1234, opportunity = abs, value = 4, desc = test)]
    },
    123 = {
        abss = [(account = 123, opportunity = abss, value = 8, desc = vip)]
    },
    12 = {
        absddd = [(account = 12, opportunity = absddd, value = 4, desc = production)],
        absooo = [(account = 12, opportunity = absooo, value = 2, desc = test)]
    }
}

o/p is sorted based on value(10->(5+4)->8->4->2)

I have tried so far = infos.stream().collect(Collectors.groupingBy(Info::getAccount, Collectors.groupingBy(r -> r.getOpportunity(), Collectors.toList()))) but its sorting randomly.

Answer 1

To sort base on the value of Info ,

1. Make the stream sorted , by comparing the value , such that grouping will execute in order.
2. When calling groupingBy , Specify LinkedHashMap in mapFactory to preserve the insertion order .

Following program demonstrates how to implement.

---

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Info {
    private String account;
    private String opportunity;
    private Integer value;
    private String desc;

    private Info(String account, String opportunity, Integer value, String desc) {
        super();
        this.account = account;
        this.opportunity = opportunity;
        this.value = value;
        this.desc = desc;
    }

    public static void main(String[] args) {
        List<Info> infos = new ArrayList<>();
        infos.add(new Info("12", "absddd", 4, "production"));
        infos.add(new Info("1234", "abss", 10, "vip"));
        infos.add(new Info("1234", "abs", 4, "test"));
        infos.add(new Info("1234", "abs", 5, "testing"));
        infos.add(new Info("123", "abss", 8, "vip"));
        infos.add(new Info("12", "absooo", 2, "test"));
        Map<String, Map<String, List<Info>>> sortedResult = infos.stream().sorted(Info::compareByValueDesc)
                .collect(Collectors.groupingBy(Info::getAccount, LinkedHashMap::new,
                        Collectors.groupingBy(r -> r.getOpportunity(), LinkedHashMap::new, Collectors.toList())));
        sortedResult.forEach((key, value) -> System.out.println(key + value.toString()));
    }

    public static int compareByValueDesc(Info other1, Info other2) {
        return -other1.value.compareTo(other2.value);
    }

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getOpportunity() {
        return opportunity;
    }

    public void setOpportunity(String opportunity) {
        this.opportunity = opportunity;
    }

    public String toString() {
        return this.value.toString();
    }
}