級聯數據生成樹形結構

原文地址:https://www.cnblogs.com/newlangwen/p/9969904.html

Tree 結構

public class TreeNode {
    private Integer key;
    private String title;
    private Integer parentId;
    private List<TreeNode> children;
 
    public Integer getKey() {
        return key;
    }
 
    public String getTitle() {
        return title;
    }
 
    public Integer getParentId() {
        return parentId;
    }
 
    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }
 
    public void setTitle(String title) {
        this.title = title;
    }
 
    public void setKey(Integer key) {
        this.key = key;
    }
 
 
    public List<TreeNode> getChildren() {
        return children;
    }
 
    public void setChildren(List<TreeNode> children) {
        this.children = children;
    }
}

Tree遞歸

5個方法實現遞歸樹形結構

邏輯:  構建樹形結構 ——  獲取樹形根菜單 —— 根據樹形根菜單獲取子菜單（遞歸調用）

public class Tree {
    List<TreeNode> nodes = new ArrayList<TreeNode>();
 
    public Tree(List<TreeNode> nodes) {
        super();
        this.nodes = nodes;
    }
 
    /**
     * 構建樹形結構
     *
     * @return
     */
    public List<TreeNode> buildTree() {
        List<TreeNode> treeNodes = new ArrayList<TreeNode>();
        List<TreeNode> rootNodes = getRootNodes();
        for (TreeNode rootNode : rootNodes) {
            buildChildNodes(rootNode);
            treeNodes.add(rootNode);
        }
        return treeNodes;
    }
 
    /**
     * 遞歸子節點
     *
     * @param node
     */
    public void buildChildNodes(TreeNode node) {
        List<TreeNode> children = getChildNodes(node);
        if (!children.isEmpty()) {
            for (TreeNode child : children) {
                buildChildNodes(child);
            }
            node.setChildren(children);
        }
    }
 
    /**
     * 獲取父節點下所有的子節點
     *
     * @param nodes
     * @param pnode
     * @return
     */
    public List<TreeNode> getChildNodes(TreeNode pnode) {
        List<TreeNode> childNodes = new ArrayList<TreeNode>();
        for (TreeNode n : nodes) {
            if (pnode.getKey().equals(n.getParentId())) {
                childNodes.add(n);
            }
        }
        return childNodes;
    }
 
    /**
     * 判斷是否爲根節點
     *
     * @param nodes
     * @param inNode
     * @return
     */
    public boolean rootNode(TreeNode node) {
        boolean isRootNode = true;
        for (TreeNode n : nodes) {
            if (node.getParentId().equals(n.getKey())) {
                isRootNode = false;
                break;
            }
        }
        return isRootNode;
    }
 
    /**
     * 獲取集合中所有的根節點
     *
     * @param nodes
     * @return
     */
    public List<TreeNode> getRootNodes() {
        List<TreeNode> rootNodes = new ArrayList<TreeNode>();
        for (TreeNode n : nodes) {
            if (rootNode(n)) {
                rootNodes.add(n);
            }
        }
        return rootNodes;
    }
}