D:
  root
      popcorn-folder1
           popcorn-subfolder1
               popcorn-subfile1
           popcorn-file1
      popcorn-folder2
           popcorn-subfolder2
           popcorn-file2

D:
  root
      folder1
           subfolder1
               subfile1
           file1
      folder2
           subfolder2
           file2

package com.din.pach;

import java.io.File;
import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.FileVisitor;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardCopyOption;
import java.nio.file.attribute.BasicFileAttributes;

public class FileNio {

public static void main(String[] args) throws IOException {

    Path sourcePath      = Paths.get("D:\root\");

    Files.walkFileTree(sourcePath, new FileVisitor<Path>() {
        @Override
        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
            // System.out.println("pre visit dir:" + dir);
            //rename(dir);
            //renameFile(dir);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
            //System.out.println("visit file: " + file);
            renameFile(file);
            System.out.println("====================================================================");
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
            //   System.out.println("visit file failed: " + file);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
            //  System.out.println("post visit directory: " + dir);
            renameDirectory(dir);
            return FileVisitResult.CONTINUE;
        }



    });



}

public static void renameFile(Path file) throws IOException {


    boolean isDirectory = Files.isDirectory(file);
    boolean isWritable = Files.isWritable(file);
    System.out.println("isDirectory-> "+isDirectory);
    System.out.println("isWritable-> "+isWritable);

    Path sourcePath      = Paths.get(file.toString());
    String origName = file.getFileName().toString();
    String newName = origName.replaceAll("POPCORN-", "");
    if (isWritable&&!isDirectory) {




        System.out.println("fname-> "+origName);
        /*get the path of the directory*/
        String baseLoc = file.getParent().toString();
        System.out.println("baseLoc-> "+baseLoc);
        if (origName.contains("POPCORN-")  /*|| origName.contains("#") || origName.contains("@")*/){

            System.out.println("Orig name-> "+origName);
            /*origName = origName.replaceAll("&", "_and_");
        origName = origName.replaceAll("@", "_at_");*/


            System.out.println("New Name-> "+newName);
            String newLoc = baseLoc+File.separator+newName;//having "/" hardcoded is not cross-platform.
            System.out.println("newLoc-> "+newLoc);
            //File newFile = new File(newLoc);


            Path destinationPath = Paths.get(newLoc);

            Files.move(sourcePath, destinationPath, StandardCopyOption.REPLACE_EXISTING);

        } else {
            System.out.println("No write permission");
        }
    }else{

        /*if(origName.contains("POPCORN-")  || origName.contains("#") || origName.contains("@")){
            Files.copy(sourcePath, sourcePath.resolveSibling(newName),StandardCopyOption.REPLACE_EXISTING);
        }*/
    }
}



public static void renameDirectory(Path file) throws IOException {


    boolean isDirectory = Files.isDirectory(file);
    boolean isWritable = Files.isWritable(file);
    System.out.println("isDirectory-> "+isDirectory);
    System.out.println("isWritable-> "+isWritable);

    Path sourcePath      = Paths.get(file.toString());
    String origName = file.getFileName().toString();
    String newName = origName.replaceAll("POPCORN-", "");
    if (isWritable&&isDirectory) {

            if(origName.contains("POPCORN-")  /*|| origName.contains("#") || origName.contains("@")*/){
                Files.move(sourcePath, sourcePath.resolveSibling(newName),StandardCopyOption.ATOMIC_MOVE);
            }

        } else {
            System.out.println("No write permission");
        }
    }
}

Exception in thread "main" java.nio.file.AccessDeniedException: D:rootPOPCORN-folder1 -> D:rootfolder1
at sun.nio.fs.WindowsException.translateToIOException(Unknown Source)
at sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
at sun.nio.fs.WindowsFileCopy.move(Unknown Source)
at sun.nio.fs.WindowsFileSystemProvider.move(Unknown Source)
at java.nio.file.Files.move(Unknown Source)
at com.din.pach.FileNio.renameDirectory(FileNio.java:121)
at com.din.pach.FileNio$1.postVisitDirectory(FileNio.java:45)
at com.din.pach.FileNio$1.postVisitDirectory(FileNio.java:1)
at java.nio.file.Files.walkFileTree(Unknown Source)
at java.nio.file.Files.walkFileTree(Unknown Source)
at com.din.pach.FileNio.main(FileNio.java:19)