012-list 转树 tree

一、概述

二、代码

public class ListTreeConvert {
    private Integer id;
    private Integer pid;
    private String name;
    private List<ListTreeConvert> children;

    ListTreeConvert(Integer id, Integer pid, String name) {
        this.id = id;
        this.pid = pid;
        this.name = name;
    }

    public ListTreeConvert() {
    }

    public Integer getId() {
        return id;
    }

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

    public Integer getPid() {
        return pid;
    }

    public void setPid(Integer pid) {
        this.pid = pid;
    }

    public String getName() {
        return name;
    }

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

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

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

    public static void main(String[] args) {
        List<ListTreeConvert> list = new ArrayList<ListTreeConvert>();
        list.add(new ListTreeConvert(1, 0, "1"));
        list.add(new ListTreeConvert(2, 0, "2"));
        list.add(new ListTreeConvert(3, 2, "3"));
        list.add(new ListTreeConvert(4, 3, "4"));
        list.add(new ListTreeConvert(5, 4, "5"));
        list.add(new ListTreeConvert(6, 5, "6"));

        List<ListTreeConvert> treeList1 = new ArrayList<>();
        List<ListTreeConvert> treeList2 = new ArrayList<>();
        List<ListTreeConvert> treeList3 = new ArrayList<>();

        String src =JSON.toJSONString(list);
        //方法一、
        treeList1 = listToTree1(JSONArray.parseArray(src,ListTreeConvert.class));
        treeList2 = listToTree2(JSONArray.parseArray(src,ListTreeConvert.class));
        treeList3 = listToTree3(JSONArray.parseArray(src,ListTreeConvert.class));

        System.out.println(JSON.toJSONString(treeList1));
        System.out.println(JSON.toJSONString(treeList2));
        System.out.println(JSON.toJSONString(treeList3));

    }


    public static List<ListTreeConvert> listToTree1(List<ListTreeConvert> list) {
        List<ListTreeConvert> treeList = new ArrayList<ListTreeConvert>();
        for (ListTreeConvert tree : list) {
            //找到根
            if (tree.getPid() == 0) {
                treeList.add(tree);
            }
            //找到子
            for (ListTreeConvert treeNode : list) {
                if (treeNode.getPid() == tree.getId()) {
                    if (tree.getChildren() == null) {
                        tree.setChildren(new ArrayList<ListTreeConvert>());
                    }
                    tree.getChildren().add(treeNode);
                }
            }
        }
        return treeList;
    }

    /**
     * 方法二、
     *
     * @param list
     * @return
     */
    public static List<ListTreeConvert> listToTree2(List<ListTreeConvert> list) {
        //用递归找子。
        List<ListTreeConvert> treeList = new ArrayList<ListTreeConvert>();
        for (ListTreeConvert tree : list) {
            if (tree.getPid() == 0) {
                treeList.add(findChildren(tree, list));
            }
        }
        return treeList;
    }

    private static ListTreeConvert findChildren(ListTreeConvert tree, List<ListTreeConvert> list) {
        for (ListTreeConvert node : list) {
            if (node.getPid() == tree.getId()) {
                if (tree.getChildren() == null) {
                    tree.setChildren(new ArrayList<ListTreeConvert>());
                }
                tree.getChildren().add(findChildren(node, list));
            }
        }
        return tree;
    }

    /**
     * 方法三
     *
     * @param list
     * @return
     */
    public static List<ListTreeConvert> listToTree3(List<ListTreeConvert> list) {
        List<ListTreeConvert> treeList = new ArrayList<ListTreeConvert>();
        for (ListTreeConvert tree : list) {
            if (tree.getPid() == 0) {
                treeList.add(tree);
            }
        }
        for (ListTreeConvert tree : list) {
            toTreeChildren(treeList, tree);
        }
        return treeList;
    }

    private static void toTreeChildren(List<ListTreeConvert> treeList, ListTreeConvert tree) {
        for (ListTreeConvert node : treeList) {
            if (tree.getPid() == node.getId()) {
                if (node.getChildren() == null) {
                    node.setChildren(new ArrayList<ListTreeConvert>());
                }
                node.getChildren().add(tree);
            }
            if (node.getChildren() != null) {
                toTreeChildren(node.getChildren(), tree);
            }
        }
    }

}