关于实现 List＜Node＞转 Tree，未知根节点条件集合树化

àì夳堔傛蜴生んèń 2021-10-09 08:56 224阅读 0赞

背景，树存在文件及文件夹。（例如操作系统中的资源管理器）

**1.首先定义两个实体**

/**
         * 文件夹 实体
         */
        @Data
        private static class Folder {
            private int id;
            private String name;
            private int fId;
    
            public Folder(int id, String name, int fId) {
                this.id = id;
                this.name = name;
                this.fId = fId;
            }
        }
    
        /**
         * 文件 实体
         */
        @Data
        private static class File {
            private int id;
            private String name;
            private int fId;
    
            public File(int id, String name, int fId) {
                this.id = id;
                this.name = name;
                this.fId = fId;
            }
        }

**2.定义两个全局变量集合，用于存储数据，模拟数据库**

private static List<Folder> folders = Lists.newArrayList();
    private static List<File> files = Lists.newArrayList();

**3.定义数据生成，静态生成，模拟数据库中数据**

static {
            //文件夹池
            folders.add(new Folder(1, "文件夹1", -1));
            folders.add(new Folder(2, "文件夹2", -1));
            folders.add(new Folder(3, "文件夹3", -1));
            folders.add(new Folder(11, "文件夹11", 1));
            folders.add(new Folder(12, "文件夹12", 1));
            folders.add(new Folder(111, "文件夹111", 11));
            folders.add(new Folder(121, "文件夹121", 12));
            folders.add(new Folder(22, "文件夹22", 2));
            folders.add(new Folder(221, "文件夹221", 22));
            folders.add(new Folder(2211, "文件夹2211", 221));
    
            //文件池
            files.add(new File(1, "文件1", 1));
            files.add(new File(2, "文件2", 1));
            files.add(new File(3, "文件3", 22));
            files.add(new File(4, "文件4", 22));
            files.add(new File(5, "文件5", 1));
            files.add(new File(6, "文件6", 22));
            files.add(new File(7, "文件7", 221));
            files.add(new File(8, "文件8", 3));
            files.add(new File(9, "文件9", 9999999));
    }

**4.定义树状 节点 载体，用于存储树中每个节点数据**

/**
         * 树 节点 载体
         */
        @Data
        private static class ResNode {
            private int id;
            private String name;
            private int fId;
            private int type;
            private List<ResNode> child;
    
            public ResNode(int id, String name, int fId, int type, List<ResNode> child) {
                this.id = id;
                this.name = name;
                this.fId = fId;
                this.type = type;
                this.child = child;
            }
    
            public ResNode(int id, String name, int fId, int type) {
                this.id = id;
                this.name = name;
                this.fId = fId;
                this.type = type;
            }
    }

**5.生成树状核心代码 有兴趣的可以 分析一下， 应该很简单**

private static ResNode getCompleteTree() {
            List<ResNode> firstLevel = Lists.newArrayList();
            //遍历所有文件夹、文件
            //寻找一级文件夹、文件（一级如何定义：没有父节点的则为一级）
            List<Folder> newFolders = Lists.newArrayListWithCapacity(folders.size());
            for (Folder folder : folders) {
                Optional<Folder> folderOpt = folders.stream().filter(f -> Objects.equal(f.id, folder.fId)).findFirst();
                if (folderOpt.isPresent()) {
                    newFolders.add(folder);
                } else {
                    firstLevel.add(new ResNode(folder.id, folder.name, folder.fId, folderType));
                }
            }
            List<File> newFiles = Lists.newArrayListWithCapacity(files.size());
            for (File file : files) {
                Optional<Folder> folderOpt = folders.stream().filter(f -> Objects.equal(f.id, file.fId)).findFirst();
                if (folderOpt.isPresent()) {
                    newFiles.add(file);
                } else {
                    firstLevel.add(new ResNode(file.id, file.name, file.fId, fileType));
                }
            }
    
            //遍历资源树一级节点，获取一级节点下所有的树状子节点
            for (ResNode resNode : firstLevel) {
                resNode.setChild(getChildTree(resNode.getId(), newFolders, newFiles));
            }
    
            //组合成完整树状
            return new ResNode(-999, "根节点", -9999, 0, firstLevel);
        }
    
        private static List<ResNode> getChildTree(int fId, List<Folder> folders, List<File> files) {
            List<ResNode> resNodes = Lists.newArrayListWithCapacity(folders.size());
            for (Folder folder : folders) {
                if (folder.fId == fId) {
                    List<ResNode> child = getChildTree(folder.id, folders, files);
                    resNodes.add(new ResNode(folder.id, folder.name, folder.fId, 1, child));
                }
            }
            for (File file : files) {
                if (file.fId == fId) {
                    resNodes.add(new ResNode(file.id, file.name, file.fId, 2, null));
                }
            }
            return resNodes;
    }

**6.定义打印 树状结构方法，用于直观表达树状结构生成结果**

static String finalStr = "    ";
        private static void printResNode(ResNode resNode, String str) {
            if (null == resNode) {
                return;
            }
            System.out.println(str + resNode.getName());
            if (CollectionUtils.isEmpty(resNode.child)) {
                return;
            }
            for (ResNode c : resNode.child) {
                printResNode(c, finalStr + str);
            }
        }

**7.运行结果如下图**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMjIzNjg4_size_16_color_FFFFFF_t_70][]

**8.所有的关键代码都在上面了，那么整体发一份，直接可以编译运行的。**

/**
     * @author WangJi
     * @Description 案例
     * @Date 2020/9/10 16:08
     */
    public class Demo {
    
        private final static int folderType = 1;
        private final static int fileType = 2;
    
    
        /**
         * 文件夹 实体
         */
        @Data
        private static class Folder {
            private int id;
            private String name;
            private int fId;
    
            public Folder(int id, String name, int fId) {
                this.id = id;
                this.name = name;
                this.fId = fId;
            }
        }
    
        /**
         * 文件 实体
         */
        @Data
        private static class File {
            private int id;
            private String name;
            private int fId;
    
            public File(int id, String name, int fId) {
                this.id = id;
                this.name = name;
                this.fId = fId;
            }
        }
    
        private static List<Folder> folders = Lists.newArrayList();
        private static List<File> files = Lists.newArrayList();
    
        static {
            //文件夹池
            folders.add(new Folder(1, "文件夹1", -1));
            folders.add(new Folder(2, "文件夹2", -1));
            folders.add(new Folder(3, "文件夹3", -1));
            folders.add(new Folder(11, "文件夹11", 1));
            folders.add(new Folder(12, "文件夹12", 1));
            folders.add(new Folder(111, "文件夹111", 11));
            folders.add(new Folder(121, "文件夹121", 12));
            folders.add(new Folder(22, "文件夹22", 2));
            folders.add(new Folder(221, "文件夹221", 22));
            folders.add(new Folder(2211, "文件夹2211", 221));
    
            //文件池
            files.add(new File(1, "文件1", 1));
            files.add(new File(2, "文件2", 1));
            files.add(new File(3, "文件3", 22));
            files.add(new File(4, "文件4", 22));
            files.add(new File(5, "文件5", 1));
            files.add(new File(6, "文件6", 22));
            files.add(new File(7, "文件7", 221));
            files.add(new File(8, "文件8", 3));
            files.add(new File(9, "文件9", 9999999));
        }
    
        /**
         * 树 节点 载体
         */
        @Data
        private static class ResNode {
            private int id;
            private String name;
            private int fId;
            private int type;
            private List<ResNode> child;
    
            public ResNode(int id, String name, int fId, int type, List<ResNode> child) {
                this.id = id;
                this.name = name;
                this.fId = fId;
                this.type = type;
                this.child = child;
            }
    
            public ResNode(int id, String name, int fId, int type) {
                this.id = id;
                this.name = name;
                this.fId = fId;
                this.type = type;
            }
        }
    
        private static ResNode getCompleteTree() {
            List<ResNode> firstLevel = Lists.newArrayList();
            //遍历所有文件夹、文件
            //寻找一级文件夹、文件（一级如何定义：没有父节点的则为一级）
            List<Folder> newFolders = Lists.newArrayListWithCapacity(folders.size());
            for (Folder folder : folders) {
                Optional<Folder> folderOpt = folders.stream().filter(f -> Objects.equal(f.id, folder.fId)).findFirst();
                if (folderOpt.isPresent()) {
                    newFolders.add(folder);
                } else {
                    firstLevel.add(new ResNode(folder.id, folder.name, folder.fId, folderType));
                }
            }
            List<File> newFiles = Lists.newArrayListWithCapacity(files.size());
            for (File file : files) {
                Optional<Folder> folderOpt = folders.stream().filter(f -> Objects.equal(f.id, file.fId)).findFirst();
                if (folderOpt.isPresent()) {
                    newFiles.add(file);
                } else {
                    firstLevel.add(new ResNode(file.id, file.name, file.fId, fileType));
                }
            }
    
            //遍历资源树一级节点，获取一级节点下所有的树状子节点
            for (ResNode resNode : firstLevel) {
                resNode.setChild(getChildTree(resNode.getId(), newFolders, newFiles));
            }
    
            //组合成完整树状
            return new ResNode(-999, "根节点", -9999, 0, firstLevel);
        }
    
        private static List<ResNode> getChildTree(int fId, List<Folder> folders, List<File> files) {
            List<ResNode> resNodes = Lists.newArrayListWithCapacity(folders.size());
            for (Folder folder : folders) {
                if (folder.fId == fId) {
                    List<ResNode> child = getChildTree(folder.id, folders, files);
                    resNodes.add(new ResNode(folder.id, folder.name, folder.fId, 1, child));
                }
            }
            for (File file : files) {
                if (file.fId == fId) {
                    resNodes.add(new ResNode(file.id, file.name, file.fId, 2, null));
                }
            }
            return resNodes;
        }
    
    
        public static void main(String[] args) {
            ResNode resNode = getCompleteTree();
    
    
            System.out.println("-----------------------------------------------------------------------------------");
            System.out.println();
            printResNode(resNode, "");
            System.out.println();
            System.out.println("-----------------------------------------------------------------------------------");
    
        }
    
        static String finalStr = "    ";
        private static void printResNode(ResNode resNode, String str) {
            if (null == resNode) {
                return;
            }
            System.out.println(str + resNode.getName());
            if (CollectionUtils.isEmpty(resNode.child)) {
                return;
            }
            for (ResNode c : resNode.child) {
                printResNode(c, finalStr + str);
            }
        }
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwMjIzNjg4_size_16_color_FFFFFF_t_70]: /images/20211009/3acd3cd61eb74d9ab0dd093e04c3ca68.png