How to create new Thread every time when is searching in directory java

Question

I have the following code:

 public void searchStringInFile(String directory, String word)
    {
        if (word != null && directory != null)
        {

            File filePath = new File(directory);
            Queue<File> queue = new LinkedList<>();
            queue.add(filePath);

            while (!queue.isEmpty())
            {
                File currentFile = queue.poll();
                File[] listOfDirectories = currentFile.listFiles();

                if (listOfDirectories != null)
                {
                    for (File file : listOfDirectories)
                    {
                        if (file.isDirectory())
                        {
                            queue.add(file);
                        }
                        else
                        {
                            Thread thread = new Thread(new Runnable()
                            {

                                @Override
                                public void run()
                                {
                                    readText(file, word);

                                }
                            });
                            thread.start();
                        }
                    }
                }
            }

        }
    }


    private void readText(File file, String word)
    {
        Scanner scan = null;
        try
        {

            scan = new Scanner(file);
            String line;
            int lineNumber = 0;
            while (scan.hasNextLine())
            {
                line = scan.nextLine();
                lineNumber++;
                if (line.contains(word))
                {
                    System.out.println("Line: " + lineNumber + " contains the word: " + word + "  at file: " + file.getAbsolutePath());
                }
            }

        }
        catch (FileNotFoundException e)
        {
            e.printStackTrace();
        }
        finally
        {
            close(scan);
        }

It is finding a String(word) in all files in directories and subdirectories. I want to make it multithreading app - when it enters a directory(or found) it must start a new Thread and start searching in the files and I don't know how to do it actually. I make it like the above code to start a new Thread every time it opens a file, but it must be when it enters the directory.

Answer 1

If I understood your question correctly and you want to start your thread behind the loop you can do it like this :

 public void searchStringInFile(String directory, String word){
    if (word == null || directory == null) {
        return;
    }

    File filePath = new File(directory);
    Queue<File> queue = new ConcurrentLinkedQueue<>();
    queue.add(filePath);

    while (!queue.isEmpty()) {
        File currentFile = queue.poll();
        File[] listOfDirectories = currentFile.listFiles();

        if (listOfDirectories != null)
        {
            new Thread(() -> {
                for (File file : listOfDirectories)
                {
                    if (file.isDirectory()) {
                        queue.add(file);
                    } else {
                       readText(file, word);
                    }
                }
            }).start();

        }
    }
}

You would need to change your Queue to ConcurrentLinkedQueue which is Thread safe implementation, because now you have several threads concurrently changing the Queue.