详解Java构建树结构的公共方法

目录

• 一、前提
• 二、代码
• 三、使用
• 1、实现TreeNode接口
• 2、使用
• 3、样例

public interface TreeNode {
    String getId();
    String getpId();
    List getChildren();
}

public class TreeBuilder {
    /**
     * @param nodes 需要构建的nodes，不要继承 TreeNode，且需要有 TreeNode 下的三个方法
     * @param pId 父id。为null则是所有pid为null的是顶级节点；不为null，则是从给的pId往下查询并构建树
     **/
    public static <T extends TreeNode> List<T> buildTree(List<T> nodes, String pId) {
        List<T> roots = new ArrayList<>();
        for (T node : nodes) {
            if (node.getId().equals(pId) || (node.getParentId() == null && (pId == null || pId.equals(node.getId())))) {
                roots.add(node);
            }
        }
        for (T root : roots) {
            buildChildren(root, nodes);
        }
        return roots;
    }
 
    private static <T extends TreeNode> void buildChildren(T node, List<T> nodes) {
        for (T child : nodes) {
            if (child.getParentId() != null && child.getParentId().equals(node.getId())) {
                node.getChildren().add(child);
                buildChildren(child, nodes);
            }
        }
    }
}

public class TreeBuilder {
     
     /**
      * @param level 级别 从1开始。1是最顶层
      **/
    public static <T extends TreeNode> List<T> buildTree(List<T> nodes, String pId, int level) {
        List<T> roots = new ArrayList<>();
        for (T node : nodes) {
            if (node.getId().equals(pId) || (node.getParentId() == null && (pId == null || pId.equals(node.getId())))) {
                roots.add(node);
            }
        }
        for (T root : roots) {
            buildChildren(root, nodes, level, 1);
        }
        return roots;
    }
 
    private static <T extends TreeNode> void buildChildren(T node, List<T> nodes, int level, int currentLevel) {
        if (currentLevel >= level) {
            return;
        }
        for (T child : nodes) {
            if (child.getParentId() != null && child.getParentId().equals(node.getId())) {
                if (node.getChildren() == null) {
                    node.setChildren(new ArrayList<>());
                }
                node.getChildren().add(child);
                buildChildren(child, nodes, level, currentLevel + 1);
            }
        }
    }
}

public class MyTreeVo implements TreeNode {
 
    /**
     * 主键
     */
    private String id;
 
    /**
     * 父节点ID
     */
    private String pId;
 
    /**
     * 子级
     */
    private List<MyTreeVo> children = Lists.newArrayList();
 
    //其他属性……
 
    public List<MyTreeVo> getChildren() {
        return children;
    }
 
    public String getId() {
        return id;
    }
 
    public String getpId() {
        return pId;
    }
 
    //其他属性的getter、setter……

List<MyTreeVo> tree = TreeUtilQz.buildTree(vos,null);
//tree就是构建好的树结构数据

{
    "data": [
        {
            "id": "e6ee51485389495cb923a122be800011",
            "pId": "",
            "name": "一、钢管钢管",
            "children": [
                {
                    "id": "e6ee51485389495cb923a122be800014",
                    "pId": "e6ee51485389495cb923a122be800011",
                    "name": "（二）嘎嘎嘎嘎嘎",
                    "children": []
                },
                {
                    "id": "e6ee51485389495cb923a122be800013",
                    "pId": "e6ee51485389495cb923a122be800011",
                    "name": "（一）顶顶顶顶",
                    "children": []
                }
            ]
        },
        {
            "id": "e6ee51485389495cb923a122be800012",
            "pId": "",
            "name": "二、噢噢噢噢",
            "children": [
                {
                    "id": "e6ee51485389495cb923a122be800015",
                    "pId": "e6ee51485389495cb923a122be800012",
                    "name": "二的下级",
                    "children": [
                        {
                            "id": "e6ee51485389495cb923a122be800016",
                            "pId": "e6ee51485389495cb923a122be800015",
                            "name": "二的下级的下级",
                            "children": []
                        }
                    ]
                }
            ]
        }
    ]
}