Java实现树形菜单的方法总结

class TreeNode {
    int id;
    int parentId;
    String name;
    List<TreeNode> children;
    // 构造函数、getters、setters省略
}
public List<TreeNode> buildTree(List<TreeNode> nodes, int parentId) {
    List<TreeNode> tree = new ArrayList<>();
    for (TreeNode node : nodes) {
        if (node.parentId == parentId) {
            node.children = buildTree(nodes, node.id);
            tree.add(node);
        }
    }
    return tree;
}

public List<TreeNode> buildTreeWithQueue(List<TreeNode> nodes) {
    if (nodes == null || nodes.isEmpty()) {
        return Collections.emptyList();
    }
    Map<Integer, TreeNode> nodeMap = nodes.stream().collect(Collectors.toMap(TreeNode::getId, node -> node));
    List<TreeNode> tree = new ArrayList<>();
    Queue<TreeNode> queue = new LinkedList<>(nodes);
    while (!queue.isEmpty()) {
        TreeNode node = queue.poll();
        if (node.parentId == 0) {
            tree.add(node);
        } else {
            TreeNode parent = nodeMap.get(node.parentId);
            if (parent.children == null) {
                parent.children = new ArrayList<>();
            }
            parent.children.add(node);
        }
    }
    return tree;
}

public List<TreeNode> buildTreeWithMap(List<TreeNode> nodes) {
    Map<Integer, List<TreeNode>> childrenMap = new HashMap<>();
    List<TreeNode> rootNodes = new ArrayList<>();
    for (TreeNode node : nodes) {
        if (node.parentId == 0) {
            rootNodes.add(node);
        } else {
            childrenMap
                .computeIfAbsent(node.parentId, k -> new ArrayList<>())
                .add(node);
        }
    }
    for (TreeNode rootNode : rootNodes) {
        rootNode.children = getChildren(rootNode.id, childrenMap);
    }
    return rootNodes;
}
private List<TreeNode> getChildren(int parentId, Map<Integer, List<TreeNode>> childrenMap) {
    List<TreeNode> children = childrenMap.get(parentId);
    if (children != null) {
        for (TreeNode child : children) {
            child.children = getChildren(child.id, childrenMap);
        }
    }
    return children;
}

CREATE TABLE tree_nodes (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL,
    path VARCHAR(255) DEFAULT '',
    parent_id INT
);

public class TreeNode {
    private int id;
    private String name;
    private String path;
    private int parentId;
    // Getter, Setter 和 Constructor
}

public void addNode(String name, int parentId, Connection connection) throws SQLException {
    String path;
    if (parentId == 0) {
        path = "/";
    } else {
        String parentPathQuery = "SELECT path FROM tree_nodes WHERE id = ?";
        try (PreparedStatement stmt = connection.prepareStatement(parentPathQuery)) {
            stmt.setInt(1, parentId);
            ResultSet rs = stmt.executeQuery();
            if (rs.next()) {
                path = rs.getString("path") + parentId + "/";
            } else {
                throw new SQLException("Parent not found");
            }
        }
    }
    String insertQuery = "INSERT INTO tree_nodes (name, path, parent_id) VALUES (?, ?, ?)";
    try (PreparedStatement stmt = connection.prepareStatement(insertQuery)) {
        stmt.setString(1, name);
        stmt.setString(2, path);
        stmt.setInt(3, parentId);
        stmt.executeUpdate();
    }
}

public List<TreeNode> getChildren(int nodeId, Connection connection) throws SQLException {
    List<TreeNode> children = new ArrayList<>();
    String pathQuery = "SELECT path FROM tree_nodes WHERE id = ?";
    String path;
    try (PreparedStatement stmt = connection.prepareStatement(pathQuery)) {
        stmt.setInt(1, nodeId);
        ResultSet rs = stmt.executeQuery();
        if (rs.next()) {
            path = rs.getString("path") + nodeId + "/";
        } else {
            throw new SQLException("Node not found");
        }
    }
    String childrenQuery = "SELECT * FROM tree_nodes WHERE path LIKE ?";
    try (PreparedStatement stmt = connection.prepareStatement(childrenQuery)) {
        stmt.setString(1, path + "%");
        ResultSet rs = stmt.executeQuery();
        while (rs.next()) {
            TreeNode node = new TreeNode();
            node.setId(rs.getInt("id"));
            node.setName(rs.getString("name"));
            node.setPath(rs.getString("path"));
            node.setParentId(rs.getInt("parent_id"));
            children.add(node);
        }
    }
    return children;
}