使用 Java 8 Stream API 将 List 转换为 Map<String, List>

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.Date;
import java.util.List;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Trip {
    private Date startTime;
    private Date endTime;
    List<Employee> empList;
}

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {
    private String name;
    private String empId;
}

public record TripEmployee(String empId, Trip trip) {}

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
class TripEmployee {
    private String empId;
    private Trip trip;
}

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

public class TripConverter {

    public static Map<String, List<Trip>> convertTripsToEmployeeMap(List<Trip> trips) {
        return trips.stream()
                .flatMap(trip -> trip.getEmpList().stream()
                        .map(emp -> new TripEmployee(emp.getEmpId(), trip))
                )
                .collect(Collectors.groupingBy(
                        TripEmployee::empId,
                        Collectors.mapping(TripEmployee::trip,
                                Collectors.toList())
                ));
    }

    public static void main(String[] args) {
        // 创建一些示例数据
        List<Employee> employees1 = new ArrayList<>();
        employees1.add(new Employee("Alice", "1"));
        employees1.add(new Employee("Bob", "2"));

        List<Employee> employees2 = new ArrayList<>();
        employees2.add(new Employee("Charlie", "3"));
        employees2.add(new Employee("Alice", "1"));

        Trip trip1 = new Trip(new java.util.Date(), new java.util.Date(), employees1);
        Trip trip2 = new Trip(new java.util.Date(), new java.util.Date(), employees2);

        List<Trip> trips = new ArrayList<>();
        trips.add(trip1);
        trips.add(trip2);

        // 进行转换
        Map<String, List<Trip>> employeeTripMap = convertTripsToEmployeeMap(trips);

        // 打印结果
        employeeTripMap.forEach((empId, tripList) -> {
            System.out.println("Employee ID: " + empId);
            tripList.forEach(trip -> System.out.println("  Trip: " + trip));
        });
    }
}