import java.io.File;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;

    public class DiskFolderCreationThread implements Runnable{

    @Override
    public void run() {
        // TODO Auto-generated method stub
        long randData = (long) (System.currentTimeMillis() + (Math.random() * 100000));
        String folderPath = File.separatorChar + "data" + File.separatorChar + "ext" + File.separatorChar + randData;
        File testFolder = new File(folderPath);
        if (!testFolder.exists()) {
            if(testFolder.mkdirs() == false)
                System.out.println(System.currentTimeMillis() + ": folder creation failed!");

        }
        String filename = testFolder + File.separator + "test.txt";
        File testFile = new File(filename);
        FileOutputStream fileOutputStream = null;
        boolean bCreated = false;
        try {
            //Thread.sleep(1000);
            if(testFolder.exists() == false) {
                System.out.println("Folder not created!");
                System.out.println("Folder: " + testFolder.getAbsolutePath() + " does not exist!");
            }else
                bCreated = true;
            fileOutputStream = new FileOutputStream(testFile);
            fileOutputStream.close();
            testFile.delete();
            testFolder.delete();

            //System.out.println("success:" + testFile.getAbsolutePath());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            System.out.println("Folder created? " + testFolder + ": " + bCreated);
            //back off and see if the folder is really created
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            System.out.println("Checking again, " + testFolder.getAbsolutePath() + " created? " + testFolder.exists());
        }

    }
    }

Loader class

    import java.util.concurrent.Executor;
    import java.util.concurrent.Executors;

    public class DiskFolderTest {
        public void start() {
            Executor executorService = Executors.newFixedThreadPool(200);
            for(int i=0;i<10000;i++)
                executorService.execute(new DiskFolderCreationThread());
        }

        public static void main(String args[]) {
            new DiskFolderTest().start();
        }
    }

 Output:

    java.io.FileNotFoundException: \data\ext\1521045935714\test.txt (The system cannot find the path specified)
        at java.io.FileOutputStream.open0(Native Method)
        at java.io.FileOutputStream.open(FileOutputStream.java:270)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:213)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:162)
        at DiskFolderCreationThread.run(DiskFolderCreationThread.java:30)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
    Folder created? \data\ext\1521045935714: true
    Checking again, C:\data\ext\1521045935714 created? false