Question

I am using java.util logging classes to create a rolling file appender. I want to create a log reader that reads from these logs as data is written to them.

The rolling log appender code works fine on its own. But once I start the reader thread new files are not created i.e. if rolling log appender is set to use 5 files it will create 1og.0, log.1, log.2 and so on but if the reader thread starts then it will only create log.0 no other files are created. I notice this in both java logging and log4j.

I am using nio to read in the log reader. So my doubt is, is creating another FileChannel on the same file creating some problem? or have I missed some basic nio stuff here that is causing problems.

here is the code..

public class Test {

     private static final long initialTime = System.currentTimeMillis();
     private static Logger logger = Logger.getLogger(Test.class.getName());
     public static void main(String[] args) {

        logger.setLevel(Level.INFO);
        try {
            BufferedReader reader = new BufferedReader(
                                            new InputStreamReader(
                                                    new FileInputStream(
                                                            new File(System.getProperty("user.dir")+File.separator+"input.dat"))));

             FileHandler handler = new FileHandler("log/test.log", 1024, 5, true);
             handler.setFormatter(new SimpleFormatter());
             logger.addHandler(handler);
             logger.setUseParentHandlers(false);
             //If I comment the next two lines the rolling appender works as expected both in java logging
             //and when using log4j. however once I start the log reader only one file is created.
             Thread logReader = new Thread(new LogReader("log/test.log.0"));
             logReader.start();
            while(reader.ready())
            {
                String strToLog = reader.readLine();
                logger.info(strToLog);
                //Only want to run this for 10 secs.
                if(System.currentTimeMillis() - initialTime > 10000)
                    System.exit(0);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally{

        }
    }

}
class LogReader implements Runnable {


    private final int BUFFER_SIZE = 1024;

    private RandomAccessFile file;

    private FileChannel chan;

    private long offset;

    private ByteBuffer buf;

    private Charset charset = Charset.forName("UTF-8");

    private String filename = "output.log";

    public LogReader(String logfile) throws IOException {
        System.out.println("Starting log reader from " + logfile);
        file = new RandomAccessFile(logfile, "r");
        offset = file.length();
        chan = file.getChannel();
        chan.position(offset);
        buf = ByteBuffer.allocateDirect(BUFFER_SIZE);
        System.out.println("Started log reader from " + logfile);
    }

    public void run() {
        //Even if I have nothing here..the problem exists..
        }
}

Answer 1

I think there might be some concurrency issues with RandomAccessFile.

I suggest you use a different class for reading the file. E.g. java.io.FileReader