如何根据“城市过滤器列表”过滤员工列表并使用 java 8 维护过滤器顺序

Question

如何根据“城市过滤器列表”过滤员工列表并使用 java 8 维护过滤器顺序。

我想根据另一个列表（filterList：引用城市）按城市名称过滤 Employee（list1）对象并创建新列表（list2）并使用 Java 8 维护 hte filterList City 顺序。

重要提示：这里的新列表应该与那里的 filterList(City name) 的顺序相同。

输入：

List<Employee> list1 = Stream.of(
                        new Employee("100","Boston","Massachusetts"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("300","pleasanton","California"),
                        new Employee("200","Decatur","Texas"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("98","sula","Maine"),
                        new Employee("156","Duluth","Ohio"))
                .collect(Collectors.toList());

过滤器列表：

List<String> filterList = Stream.of("pleasanton", "Atlanta", "Cumming", "Boston").collect(Collectors.toList());

预期 output：

List<Employee> list2 = Stream.of(
                        new Employee("300","pleasanton","California"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("100","Boston","Massachusetts"))
                .collect(Collectors.toList());

Answer 1

尝试这个：

import java.util.*;
import java.util.stream.*;
class Employee {
    private String salary;
    private String city;
    private String state;
    
    public Employee(String salary, String city, String state) {
        this.salary = salary;
        this.city = city;
        this.state = state;
    }
    
    public String getSalary() {
        return salary;
    }
    
    public String getCity() {
        return city;
    }
    
    public String getState() {
        return state;
    }
}

public class Main {
    public static void main(String[] args) {
        List<Employee> list1 = Stream.of(
                        new Employee("100","Boston","Massachusetts"),
                        new Employee("400","Atlanta","Georgia"),
                        new Employee("300","pleasanton","California"),
                        new Employee("200","Decatur","Texas"),
                        new Employee("500","Cumming","Atlanta"),
                        new Employee("98","sula","Maine"),
                        new Employee("156","Duluth","Ohio"))
                .collect(Collectors.toList());
        
        List<String> filterList = Stream.of("pleasanton", "Atlanta", "Cumming", "Boston").collect(Collectors.toList());
        
        List<Employee> list2 = list1.stream().filter(e -> filterList.contains(e.getCity())).sorted((a, b) -> filterList.indexOf(a.getCity()) - filterList.indexOf(b.getCity())).collect(Collectors.toList());
    list2.stream().forEach(e -> {
                System.out.println("City " + e.getCity());
                System.out.println("State " + e.getState());
                System.out.println("Salary " + e.getSalary());
                System.out.println();
        });
    }
}

Answer 2

嗯，这是一个多步骤的过程。 首先，我认为创建中间流没有任何意义，只是为了创建Collection 。 还有更多的Collection库方法，例如旧的Arrays.asList ，您可以使用它们轻松创建集合，而无需创建不必要的中间对象。 这是您问题的线性时间解决方案。

final List<String> filterList = Arrays.asList("pleasanton", "Atlanta", "Cumming", "Boston");

final Map<String, Integer> posMap = IntStream.range(0, filterList.size()).boxed()
        .collect(Collectors.toMap(filterList::get, i -> i));
final Set<String> cities = new HashSet<>(filterList);
final Collection<Employee> sortedEmps = list1.stream().filter(e -> cities.contains(e.getCity()))
    .sorted(Comparator.comparing(e -> posMap.get(e.getCity()))).collect(Collectors.toList()); 

请注意，您根据元素在输入数组中的位置对元素进行排序，并且使用Set来检查包含性会将其他二次时间解带入线性解。

Answer 3

我们可以使用 Comparator.comparingInt，而不是使用 indexOf 进行比较：

class Main {
public static void main(String[] args) {
    List<Employee> list = Stream.of(new Employee("100", "Boston", "Massachusetts"),
                    new Employee("400", "Atlanta", "Georgia"),
                    new Employee("300", "pleasanton", "California"),
                    new Employee("200", "Decatur", "Texas"),
                    new Employee("500", "Cumming", "Atlanta"),
                    new Employee("98", "sula", "Maine"),
                    new Employee("156", "Duluth", "Ohio"))
            .collect(Collectors.toList());
    List<String> filterList = Stream.of("pleasanton", "Atlanta", "Cumming", "Boston").collect(Collectors.toList());
    List<Employee> collect = list.stream().filter(re -> filterList.contains(re.getCity())).sorted(Comparator.comparingInt(a -> filterList.indexOf(a.getCity()))).collect(Collectors.toList());
    collect.stream()
            .forEach(e->{
                System.out.println("City" + e.getCity());
                System.out.println("State " + e.getState());
                System.out.println("Salary " + e.getSalary());
                System.out.println();
            });
}

}