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stream流中的多级分组

时间: 2025-02-12 16:13:06 浏览: 39

### Java Stream API 实现多级分组在处理复杂数据结构时，Java Stream API 提供了强大的工具来简化集合的操作。对于多级分组的需求，可以利用 `Collectors.groupingBy` 方法嵌套调用来实现。下面是一个具体的例子，展示如何在一个员工列表中按部门和职位进行两级分组： ```java import java.util.*; import java.util.stream.Collectors; class Employee { private String name; private String department; private String position; public Employee(String name, String department, String position) { this.name = name; this.department = department; this.position = position; } // Getters and setters omitted for brevity @Override public String toString() { return "Employee{name='" + name + "', department='" + department + "', position='" + position + "'}"; } } public class MultiLevelGroupingExample { public static void main(String[] args) { List<Employee> employees = Arrays.asList( new Employee("Alice", "HR", "Manager"), new Employee("Bob", "Engineering", "Developer"), new Employee("Charlie", "HR", "Recruiter"), new Employee("David", "Engineering", "QA Engineer") ); Map<String, Map<String, List<Employee>>> result = employees.stream() .collect(Collectors.groupingBy(Employee::getDepartment, Collectors.groupingBy(Employee::getPosition))); System.out.println(result); } } ``` 这段代码创建了一个包含四个不同员工的对象列表，并按照他们的所属部门以及具体职位进行了两次分组操作[^1]。最终的结果是以部门作为外层键值，内部再以职位为键构建的一个双重映射表。

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