Java Logger wont log into file

Question

I can't make my logger to work. Inside my code I have these lines :

private static final Logger log = Logger.getLogger(ServerThread.class.getName());
log.setUseParentHandlers(false);
FileHandler fh = new FileHandler("ex.txt", true);
SimpleFormatter sf = new SimpleFormatter();
fh.setFormatter(sf);
log.addHandler(fh);
log.setLevel(Level.FINE);

And later when I get input from user :

log.log(Level.FINE,inputString);

But all that happens is that fileHandler creates a file ex.txt, but nothing is logged into the file. I am sure that log.log() is being executed.

Does `fh.flush()` change anything? It shouldn't, since the logger should automatically flush after each record, but it might be worth a try to get closer to the issue. — dhke, Jul 08 '17 at 16:20

score 0 · Answer 1 · edited Jul 21 '17 at 06:35

You can also use this simple approach.

public static Logger logger;

public static Logger startLogger() {

    DateFormat dateFormat = new SimpleDateFormat("yyyyMMdd-HH-mm-ss");
    Date date = new Date();
    String datefor = dateFormat.format(date);

    logger = Logger.getLogger("MyLog");

    PropertyConfigurator.configure(CLASSPATH + "/" + "log4j.properties");
    Appender appender = null;
    try {

        appender = new FileAppender(new SimpleLayout(), CLASSPATH  + "/log/MyLogFile" + datefor + ".log");
        logger.addAppender(appender);
        appender.setLayout(new SimpleLayout());
    } catch (SecurityException exception) {
        exception.printStackTrace();
    } catch (IOException exception) {
        exception.printStackTrace();
    }
}

score 0 · Accepted Answer · answered Jul 10 '17 at 14:12

Make sure that you only create one FileHandler and ensure that your adjust the level of your FileHandler too.

private static final Logger log = Logger.getLogger(ServerThread.class.getName());
private static final FileHandler fh;
static {
    try {
        log.setUseParentHandlers(false);
        fh = new FileHandler("ex.txt", true);
        fh.setFormatter(new SimpleFormatter());
        fh.setLevel(Level.FINE);
        log.addHandler(fh);
        log.setLevel(Level.FINE);
    } catch (IOException ioe) {
        throw new ExceptionInInitializerError(ioe);
    }
}

If you still don't see results then you should print the logger tree to ensure that the filehander and the loggers are created in the layout you are expecting.

In general, you should should setup a logging.properties file.

Java Logger wont log into file

2 Answers2