Calling close() on OutputStream is cutting off output to a log file

Question

I was looking into a problem with .close() causing cut-off issues. The program is running on two different servers, but had the same cutoff issue. It appears that the log file is not flushing properly. So I decided to dig into the .close() source code. I don't see a .flush() being called. Am I missing something? Should we always call .flush()? According to this answer, it shouldn't matter: Using flush() before close()

What I'm calling:

    private static void write_to_file(String incoming){
    output_stream.write(incoming);
    output_stream.write(System.lineSeparator());
    }

Later on I call output_stream.close();

The source code:

 /**
 * Closes the stream and releases any system resources associated
 * with it. Closing a previously closed stream has no effect.
 *
 * @see #checkError()
 */
public void close() {
    try {
        synchronized (lock) {
            if (out == null)
                return;
            out.close();
            out = null;
        }
    }
    catch (IOException x) {
        trouble = true;
    }
}

Log file:

C:\apps\bot\log\processed\file.0000090.gz
C:\apps\bot\log\processed\file.0000091.gz
C:\apps\bot\log\process

Using `close()` should be all you need. How do you create the stream you are writing to? Are you absolutely sure that your `close()` method gets called? — Mifeet, May 02 '16 at 19:20
You know what, I had just checked that and saw it was only being executed in a try-catch block (on any exception). Please leave an answer and I will mark correct. Thanks — Petro, May 02 '16 at 19:24

score 2 · Accepted Answer · edited May 23 '17 at 10:33

As stated in the question you've correctly pointed out, calling close() on a stream is enough to flush whatever you've written to the stream. If the output is truncated, there are a few common pitfalls:

Your close() method is not called, e.g. if you put it in a catch block instead of finally ;)
Calling close() on a custom stream doesn't propagate the call to the underlying stream.
The problem can also be in encoding if you don't properly convert your String to bytes.

Calling close() on OutputStream is cutting off output to a log file

1 Answers1