fragment of code from https://github.com/RodionGork/RandomDocuments

Generator.java

    public void generate(String path) {
        System.out.println("Creating " + cores + " threads...");
        ExecutorService service = Executors.newFixedThreadPool(cores);
        prepareWords(false);
        for (int i = 0; i < numFiles; i++) {
            String name = String.format("%s/%08d.txt", path, i);
            service.execute(new FileGenerator(name));
        }
        service.shutdown();
        try {
            service.awaitTermination(1, TimeUnit.DAYS);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
    
    private class FileGenerator implements Runnable {
        
        private String name;
        
        public FileGenerator(String name) {
            this.name = name;
        }
        
        public void run() {
            try (OutputStream output = new BufferedOutputStream(new FileOutputStream(name))) {
                generateFile(output);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        
        private void generateFile(OutputStream output) throws IOException {
            int size = rnd.nextInt(maxSize - minSize + 1) + minSize;
            int cnt = 0;
            while (size > 0) {
                pos = (pos + rnd.nextInt(5) + 1) % words.length;
                byte[] w = words[pos];
                output.write(w, 0, w.length);
                cnt += w.length + 1;
                if (cnt < lineLength) {
                    output.write(' ');
                } else {
                    output.write('\n');
                    size -= cnt;
                    cnt = 0;
                }
            }
        }
        
    }