如何根据 objects 的某些字段在列表中组合 2 个或更多 objects

Question

如果标题听起来含糊不清，我很抱歉。

我有一个 object -

    public class AccountInfo {
        private String accountId;
        private Double vat;
        private Double totalFee;
        private Date invoiceDate;
    }

并且有这些 objects-

的列表

List<AccountInfo> AccountInfoLst;

我想通过将 objects 与相同的 accountId 相加来操纵此列表，方法是将 vat 和 totalFee 字段，前提是它们也具有相同的 invoiceDate。

如果两个 object 具有相同的 accountId 但不同的 invoiceDate，则不应合并它们。

Answer 1

遍历重复的列表，将它们合并为一个 AccountInfo 并删除所有重复项。

由于日期已弃用，我们使用了 java.time.LocalDate。

代码：

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class AccountInfo {
    private String accountId;

    private Double vat;
    private Double totalFee;
    private LocalDate invoiceDate;

    public Double getVat() {
        return vat;
    }

    public void setVat(Double vat) {
        this.vat = vat;
    }

    public Double getTotalFee() {
        return totalFee;
    }

    public void setTotalFee(Double totalFee) {
        this.totalFee = totalFee;
    }

    public LocalDate getInvoiceDate() {
        return invoiceDate;
    }

    public void setInvoiceDate(LocalDate invoiceDate) {
        this.invoiceDate = invoiceDate;
    }

    public AccountInfo(String accountId, Double vat, Double totalFee, LocalDate invoiceDate) {
        this.accountId = accountId;
        this.vat = vat;
        this.totalFee = totalFee;
        this.invoiceDate = invoiceDate;
    }

    public String getAccountId() {
        return accountId;
    }

    public void setAccountId(String accountId) {
        this.accountId = accountId;
    }

    public String toString() {
        return accountId + " " + vat + " " + totalFee + " " + invoiceDate;
    }

    public boolean areEquals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        AccountInfo that = (AccountInfo) o;
        var thatInvoiceDate = that.getInvoiceDate();
        var thisInvoiceDate = getInvoiceDate();
        return that.getAccountId().equals(getAccountId()) && thatInvoiceDate.isEqual(thisInvoiceDate);
    }

    @Override
    public int hashCode() {
        return Objects.hash(accountId, vat, totalFee, invoiceDate);
    }
}

public class MainClass {
    public static void main(String... $) {
        var out = System.out;
        
        List<AccountInfo> accounts = Stream.of(new AccountInfo("A", 20.2, 200.4, LocalDate.of(2022, 11, 3))
                , new AccountInfo("A", 20.2, 200.4, LocalDate.of(2022, 11, 3)),
                new AccountInfo("B", 20.2, 200.4, LocalDate.of(2023, 11, 2)),
                new AccountInfo("B", 20.2, 200.4, LocalDate.of(2023, 11, 2))).collect(Collectors.toList());
        
        //Iterating over all the accounts
        for (int i = 0; i < accounts.size(); i++) {
            var account = accounts.get(i);
            ArrayList<AccountInfo> duplicates = new ArrayList<>();
            for (int j = i + 1; j < accounts.size(); j++) {
                var acc = accounts.get(j);
                if (acc.areEquals(account))
                    duplicates.add(acc);
            }
//            out.println(i + " " + indices);
            //Merging all duplicates to account
            for (AccountInfo acc : duplicates) {
                account.setTotalFee(acc.getTotalFee() + account.getTotalFee());
                account.setVat(acc.getVat() + account.getVat());
            }
            //Removing all duplicates
            accounts.removeAll(duplicates);
        }
        //printing accounts after removal of duplicates
        out.println(accounts);
    }
}

输出：

[A 40.4 400.8 2022-11-03, B 40.4 400.8 2023-11-02]

Answer 2

如果您想利用 Streams 实现，一种可能的方法是将 collect 数据放入 Map，用作键组合 accountId 和 invoiceDate.

的对象

映射到相同密钥的所有帐户将合并。

在 accountId 或 invoiceDate 中不同的帐户将保持不变。

另一种选择是创建嵌套地图。其中 accountId 将用作键，值将是一个映射，该映射将依次使用 invoiceDate 作为键，值将是 AccountInfo.

public static void main(String[] args) { List<AccountInfo> result = List.of( new AccountInfo("123", 80., 180., LocalDate.now()), new AccountInfo("123", 120., 590., LocalDate.now()), new AccountInfo("123", 30., 120., LocalDate.now().minusDays(3)) ) .stream() .collect(Collectors.toMap( AccountWrapper::new, UnaryOperator.identity(), (acc1, acc2) -> new AccountInfo( acc1.getAccountId(), acc1.getVat() + acc2.getVat(), acc1.getTotalFee() + acc2.getTotalFee(), acc1.getInvoiceDate()) )) .values().stream() .collect(Collectors.toList()); result.forEach(System.out::println); } public record AccountWrapper(String accountId, LocalDate invoiceDate) { public AccountWrapper(AccountInfo info) { this(info.getAccountId(), info.getInvoiceDate()); } }

如果您使用 Java 15 或更早版本 AccountWrapper 可以作为 常规 class 实现：

public class AccountWrapper { private final String accountId; private final LocalDate invoiceDate; public AccountWrapper(AccountInfo info) { this.accountId = info.getAccountId(); this.invoiceDate = info.getInvoiceDate(); } @Override public int hashCode() { return Objects.hash(accountId, invoiceDate); } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; AccountWrapper other = (AccountWrapper) o; return accountId.equals(other.accountId) && invoiceDate.equals(other.invoiceDate); } }

带有嵌套地图的版本，不需要辅助对象

List<AccountInfo> result = List.of( new AccountInfo("123", 80., 180., LocalDate.now()), new AccountInfo("123", 120., 590., LocalDate.now()), new AccountInfo("123", 30., 120., LocalDate.now().minusDays(3)) ) .stream() .collect(Collectors.groupingBy( AccountInfo::getAccountId, Collectors.toMap( AccountInfo::getInvoiceDate, UnaryOperator.identity(), (acc1, acc2) -> new AccountInfo( acc1.getAccountId(), acc1.getVat() + acc2.getVat(), acc1.getTotalFee() + acc2.getTotalFee(), acc1.getInvoiceDate()) ))) .values().stream() .flatMap(map -> map.values().stream()) .collect(Collectors.toList()); result.forEach(System.out::println);

输出

AccountInfo{accountId='123', vat=200.0, totalFee=770.0, invoiceDate=2022-02-09} AccountInfo{accountId='123', vat=30.0, totalFee=120.0, invoiceDate=2022-02-06}

如何根据 objects 的某些字段在列表中组合 2 个或更多 objects

How to combine 2 or more objects in a list based on certain fields of those objects

java

java-8

java-stream

代码：

输出：