java - 在java中从文件夹ID和父ID创建文件夹

Question

我需要创建一个类来获取存储在数据库中的文件夹列表，并在本地计算机上以正确的层次结构创建它们。

文件夹在数据库中的排列方式如下:

id name parent_id1 documents 02 movies 03 videos 04 my files 15 desktop 06 other 4

So documents, movies, videos and desktop are in the root. 'my files' goes in the folder with the id of 1(documents) and 'other' goes in the folder with the id of 4(my files)

I have been trying to do it by using a whyle loop but dont know how to get them to go into the correct folders.

try {
            con = DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        while( i < 50 )
        {   
            try {            

            Statement st = con.createStatement();
            ResultSet result = st.executeQuery("SELECT name, id, parent_id FROM categories WHERE parent_id = '"+PID+"' AND repository_id = '"+RepoID+"'");



            while (result.next ())
            {
                String FolderName = result.getString ("name");
                String FolderId = result.getString ("id");
                String FolderId = result.getString ("parent_id");
make the folder name here
                System.out.println( FolderName+" "+FolderId );
            }

            System.out.println( " ");
                    i++ ;
            PID++;
            } catch (SQLException ex) {
                 System.out.println(ex.getMessage());
             }
            }

Answer 1

创建一个文件夹对象来存储数据，然后在您从数据库中读取数据时构建这些对象。构建完所有 Folder 对象后，执行最后一个循环以将每个 Folder 绑定(bind)到其父类。也许是这样的:

class Folder {
    private String name;
    private int id;
    private int parentId;
    private List<Folder> children = new ArrayList<Folder>();

    public Folder(String name, int id, int parentId) {
        this.name = name;
        this.id = id;
        this.parentId = parentId;
    }

    public void addChildFolder(Folder folder) {
        this.children.add(folder);
    }

    public List<Folder> getChildren() {
        return Collections.unmodifiableList(children);
    }

    public int getParentFolderId() {
        parentId;
    }

    public String getName() {
        return name;
    }

    public int getId() {
        return id;
    }
}

现在当您从数据库中读取数据时，您创建了这些 Folder 对象(没有子对象)并将它们添加到 map 中:

Map<Integer, Folder> data = new HashMap<Integer, Folder>();

... loop through your result set getting folder data...
Folder newFolder = new Folder(nameString, id, parentId);
data.put(newFolder.getId(), newFolder);

使用 Integer.valueOf(String) 将 String 转换为 int。

一旦创建了所有文件夹，就可以进行最后一个循环，将父文件夹连接到子文件夹，如下所示:

for(Folder folder : data.values()) {
    int parentId = folder.getParentFolderId();
    Folder parentFolder = data.get(parentId);
    if(parentFolder != null)
        parentFolder.addChildFolder(folder);
}

最后，只需获取 ID 为 0 的文件夹并开始在磁盘上构建文件，使用 folder.getChildren() 作为向下移动树的便捷方式。查看 File 对象上的 javadoc，您会特别想使用 mkdirs() 方法。

希望对您有所帮助。