Log using BufferedReader and ScheduledExecutor

Question

I'm currently studying for my JAVA SE OCP Certification so and playing around with things to learn.

I'm currently on IO chapter. I'm trying to combine a ScheduledExecutor with a BufferedWriter

ScheduledExecutorService service = null;
try (BufferedWriter bw = new BufferedWriter(new FileWriter(testFile))) {
    service = Executors.newSingleThreadScheduledExecutor();
    service.scheduleAtFixedRate(() -> {
        try {
            bw.write("Curr Time: " + LocalTime.now());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }, 1, 1, TimeUnit.SECONDS);
}

I expected to write the LocalTime every second on a new line on my TestFile but this IOException shows up:

java.io.IOException: Stream closed
at java.io.BufferedWriter.ensureOpen(BufferedWriter.java:116)
at java.io.BufferedWriter.write(BufferedWriter.java:221)
at java.io.Writer.write(Writer.java:157)
at Worksheet.lambda$main$0(Worksheet.java:56)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) {...}

I think that `try-with resource` will close the buffer from the main thread so other threads inside the ThreadPool will see it as closed as soon as they try to write to it. That is why you see this error. — Michał Krzywański, Aug 21 '19 at 15:09
I just changed the try-with resource for a normal try-catch block. No more Exceptions are thrown but nothing is written on the file. — Marian Gabriel Neacsu, Aug 21 '19 at 15:13

razumichin · Accepted Answer · 2019-08-21T16:06:09.883

0

Try with:

ScheduledExecutorService service = null;
    service = Executors.newSingleThreadScheduledExecutor();
    try {
        BufferedWriter bw = new BufferedWriter(new FileWriter(testFile, true));
        service.scheduleAtFixedRate(() -> {
            try {
                bw.write("Curr Time: " + LocalTime.now() + "\n");
                bw.flush();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }
        }, 1, 1, TimeUnit.SECONDS);

    } catch (IOException ioe) {
        ioe.printStackTrace();
    }

The true parameter in the FileWriter will append each new line to the existing file, instead of creating a new file.

edited Aug 21 '19 at 16:06

answered Aug 21 '19 at 15:15

razumichin

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While this works perfectly, won't this create a new BufferedWriter object every SingleThreadScheduled run leading to non-efficient code? – Marian Gabriel Neacsu Aug 21 '19 at 15:24
This will work because `BufferedWriter` is thread safe as explained [`here`](https://stackoverflow.com/questions/30080560/is-writting-on-file-using-bufferwriter-initialized-by-filewriter-thread-safe-or) – Michał Krzywański Aug 21 '19 at 16:40

Log using BufferedReader and ScheduledExecutor

1 Answers1