check and process once in n sec using java

Question

I have a requirement in which I have to check whether any file exists in the folder. If yes, then I need to process it one by one. With my basic knowledge I have arrived to a code structure which I have posted below.

I'm creating an infinite loop and checking whether the file exists in that folder. If yes, then I'm creating a thread and processing it, else it waits for a min and checks again.

class sample {    
    synchronized int getNoOfFiles() {
        // get number of files in the folder
    }    
    synchronized void openFile() {
        // open one file
    }
    synchronized void getFileContents() {
        // get the file content
    }
    synchronized void processFileContent() {
        //performing some operation on file contents
    }    
    synchronized void closeFile() {
        //closing the file
    }    
    synchronized void deleteFile() {
        //delete the file
    }

}    
class Test {    
    public static void main(String args[]) {
        int flag=0;
        Sample obj = new Sample();
        while(1) {
            flag = obj.getNoOfFiles();    
            if(flag) {
                for(i=0;i<flag;i++) {
                    MyThread1 t1 = new MyThread1() {
                        public void run() {
                            obj.openFile();
                            obj.getFileContents();
                            obj.processFileContent();
                            obj.closeFile();
                            obj.deleteFile();
                        }
                    };    
                    t1.start();
                }
            }
            else {
                try {
                    Thread.sleep(60000);
                }
            }    
        }
    }    
}

Threads do not get garbage-collected. So your code already creates a new thread in every loop. Even if 't1' were to reference a thread that is still processing a file, this thread would not stop running. A new one would be instantiated, referenced by 't1' and started though. — Tobias, Oct 18 '12 at 19:55
oh yeah. so , i am not in need of this for loop (just now edited the code). How could i stall the thread creation until one thread finishes the entire process. can you help me for that — srinath, Oct 18 '12 at 20:01
Why would you want to do this? If you create a thread and then just wait for the thread to finish, why use concurrency at all? — Tobias, Oct 18 '12 at 20:05
can you show up a code structure for this if possible. that would help me a lot — srinath, Oct 18 '12 at 20:08
As the answers suggest I would advise using a Timer or Executor. If you are interested in when exactly a thread has finished, use a callback. — Tobias, Oct 18 '12 at 20:12

score 3 · Answer 1 · edited May 23 '17 at 11:43

Instead of doing this kind of thing yourself, I suggest you take a look at the Timer class, that can be used to do recurring tasks. Because messing around with threads manually can often result in weird bugs.

Even better would be ScheduledThreadPoolExecutor, ~~but it might be a bit complicated if you've never used executors before.~~ See Keppil's answer for how to do this.

The differences between the two are nicely summed up here: Java Timer vs ExecutorService?.

score 2 · Accepted Answer · answered Oct 18 '12 at 20:08

I would suggest using a ScheduledExecutorService:

ScheduledExecutorService executor = new ScheduledThreadPoolExecutor(1);
executor.scheduleAtFixedRate(new Runnable() {
        public void run()
        {
            obj.openFile();
            obj.getFileContents();
            obj.processFileContent();
            obj.closeFile();
            obj.deleteFile();
         }
    }, 0, 1, TimeUnit.MINUTES);

check and process once in n sec using java

2 Answers2