JDK8新特性之Stream流的应用（一）

需求是生成部门的树结构，这个需要递归循环部门列表查找部门子级，其耗时会因为其层级与成员的多寡而不断的增长，为了提高效率，使用了JDK8新特性---Stream流。

package com.tinghs.utils;

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

public class Department {

    private Integer id;

    private String name;

    private Integer parentId;

    private List<Department> children = new ArrayList<>();

    public Department(Integer id, String name, Integer parentId) {
        this.id = id;
        this.name = name;
        this.parentId = parentId;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getParentId() {
        return parentId;
    }

    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }

    public List<Department> getChildren() {
        return children;
    }

    public void setChildren(List<Department> children) {
        this.children = children;
    }

    private static List<Department> makeTree(List<Department> departmentList, Integer pId) {

        //子部门
        List<Department> children = departmentList.stream().filter(x -> x.getParentId() == pId).collect(Collectors.toList());

        //后辈中的非子级
        List<Department> successor = departmentList.stream().filter(x -> x.getParentId() != pId).collect(Collectors.toList());

        children.forEach(x ->
                {
                    makeTree(successor, x.getId()).forEach(
                            y -> x.getChildren().add(y)
                    );
                }
        );

        return children;

    }
}