您如何先分组然后使用Java流应用过滤？
示例 ：考虑此类Employee：我想按部门分组，列出薪水大于2000的雇员。
public class Employee {
private String department;
private Integer salary;
private String name;
//getter and setter
public Employee(String department, Integer salary, String name) {
this.department = department;
this.salary = salary;
this.name = name;
}
}
这就是我可以做到的
List list = new ArrayList<>();
list.add(new Employee("A", 5000, "A1"));
list.add(new Employee("B", 1000, "B1"));
list.add(new Employee("C", 6000, "C1"));
list.add(new Employee("C", 7000, "C2"));
Map> collect = list.stream()
.filter(e -> e.getSalary() > 2000)
.collect(Collectors.groupingBy(Employee::getDepartment));
输出量
{A=[Employee [department=A, salary=5000, name=A1]],
C=[Employee [department=C, salary=6000, name=C1], Employee [department=C, salary=7000, name=C2]]}
由于B部门中没有雇员的薪水高于2000。因此B部门没有密钥： 但是实际上，我想使用空列表作为密钥–
预期产量
{A=[Employee [department=A, salary=5000, name=A1]],
B=[],
C=[Employee [department=C, salary=6000, name=C1], Employee [department=C, salary=7000, name=C2]]}
我们应该怎么做？
转播
