Class Tailer

  • All Implemented Interfaces:
    java.lang.Runnable

    public class Tailer
    extends java.lang.Object
    implements java.lang.Runnable
    Simple implementation of the unix "tail -f" functionality.

    1. Create a TailerListener implementation

    First you need to create a TailerListener implementation (TailerListenerAdapter is provided for convenience so that you don't have to implement every method).

    For example:

      public class MyTailerListener extends TailerListenerAdapter {
          public void handle(String line) {
              System.out.println(line);
          }
      }

    2. Using a Tailer

    You can create and use a Tailer in one of three ways:

    An example of each of these is shown below.

    2.1 Using the static helper method

          TailerListener listener = new MyTailerListener();
          Tailer tailer = Tailer.create(file, listener, delay);

    2.2 Using an Executor

          TailerListener listener = new MyTailerListener();
          Tailer tailer = new Tailer(file, listener, delay);
    
          // stupid executor impl. for demo purposes
          Executor executor = new Executor() {
              public void execute(Runnable command) {
                  command.run();
               }
          };
    
          executor.execute(tailer);
     

    2.3 Using a Thread

          TailerListener listener = new MyTailerListener();
          Tailer tailer = new Tailer(file, listener, delay);
          Thread thread = new Thread(tailer);
          thread.setDaemon(true); // optional
          thread.start();

    3. Stopping a Tailer

    Remember to stop the tailer when you have done with it:

          tailer.stop();
     

    4. Interrupting a Tailer

    You can interrupt the thread a tailer is running on by calling Thread.interrupt().

          thread.interrupt();
     

    If you interrupt a tailer, the tailer listener is called with the InterruptedException.

    The file is read using the default charset; this can be overridden if necessary.

    Since:
    2.0, 2.5 Updated behavior and documentation for Thread.interrupt()
    See Also:
    TailerListener, TailerListenerAdapter
    • Field Summary

      Fields 
      Modifier and Type Field Description
      private java.nio.charset.Charset charset
      The character set that will be used to read the file.
      private static java.nio.charset.Charset DEFAULT_CHARSET  
      private static int DEFAULT_DELAY_MILLIS  
      private long delayMillis
      The amount of time to wait for the file to be updated.
      private boolean end
      Whether to tail from the end or start of file
      private java.io.File file
      The file which will be tailed.
      private byte[] inbuf
      Buffer on top of RandomAccessFile.
      private TailerListener listener
      The listener to notify of events when tailing.
      private static java.lang.String RAF_MODE  
      private boolean reOpen
      Whether to close and reopen the file whilst waiting for more input.
      private boolean run
      The tailer will run as long as this value is true.
    • Constructor Summary

      Constructors 
      Constructor Description
      Tailer​(java.io.File file, java.nio.charset.Charset charset, TailerListener listener, long delayMillis, boolean end, boolean reOpen, int bufSize)
      Creates a Tailer for the given file, with a specified buffer size.
      Tailer​(java.io.File file, TailerListener listener)
      Creates a Tailer for the given file, starting from the beginning, with the default delay of 1.0s.
      Tailer​(java.io.File file, TailerListener listener, long delayMillis)
      Creates a Tailer for the given file, starting from the beginning.
      Tailer​(java.io.File file, TailerListener listener, long delayMillis, boolean end)
      Creates a Tailer for the given file, with a delay other than the default 1.0s.
      Tailer​(java.io.File file, TailerListener listener, long delayMillis, boolean end, boolean reOpen)
      Creates a Tailer for the given file, with a delay other than the default 1.0s.
      Tailer​(java.io.File file, TailerListener listener, long delayMillis, boolean end, boolean reOpen, int bufSize)
      Creates a Tailer for the given file, with a specified buffer size.
      Tailer​(java.io.File file, TailerListener listener, long delayMillis, boolean end, int bufSize)
      Creates a Tailer for the given file, with a specified buffer size.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static Tailer create​(java.io.File file, java.nio.charset.Charset charset, TailerListener listener, long delayMillis, boolean end, boolean reOpen, int bufSize)
      Creates and starts a Tailer for the given file.
      static Tailer create​(java.io.File file, TailerListener listener)
      Creates and starts a Tailer for the given file, starting at the beginning of the file with the default delay of 1.0s
      static Tailer create​(java.io.File file, TailerListener listener, long delayMillis)
      Creates and starts a Tailer for the given file, starting at the beginning of the file
      static Tailer create​(java.io.File file, TailerListener listener, long delayMillis, boolean end)
      Creates and starts a Tailer for the given file with default buffer size.
      static Tailer create​(java.io.File file, TailerListener listener, long delayMillis, boolean end, boolean reOpen)
      Creates and starts a Tailer for the given file with default buffer size.
      static Tailer create​(java.io.File file, TailerListener listener, long delayMillis, boolean end, boolean reOpen, int bufSize)
      Creates and starts a Tailer for the given file.
      static Tailer create​(java.io.File file, TailerListener listener, long delayMillis, boolean end, int bufSize)
      Creates and starts a Tailer for the given file.
      long getDelay()
      Return the delay in milliseconds.
      java.io.File getFile()
      Return the file.
      protected boolean getRun()
      Gets whether to keep on running.
      private long readLines​(java.io.RandomAccessFile reader)
      Read new lines.
      void run()
      Follows changes in the file, calling the TailerListener's handle method for each new line.
      void stop()
      Allows the tailer to complete its current loop and return.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • DEFAULT_CHARSET

        private static final java.nio.charset.Charset DEFAULT_CHARSET
      • inbuf

        private final byte[] inbuf
        Buffer on top of RandomAccessFile.
      • file

        private final java.io.File file
        The file which will be tailed.
      • charset

        private final java.nio.charset.Charset charset
        The character set that will be used to read the file.
      • delayMillis

        private final long delayMillis
        The amount of time to wait for the file to be updated.
      • end

        private final boolean end
        Whether to tail from the end or start of file
      • listener

        private final TailerListener listener
        The listener to notify of events when tailing.
      • reOpen

        private final boolean reOpen
        Whether to close and reopen the file whilst waiting for more input.
      • run

        private volatile boolean run
        The tailer will run as long as this value is true.
    • Constructor Detail

      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener)
        Creates a Tailer for the given file, starting from the beginning, with the default delay of 1.0s.
        Parameters:
        file - The file to follow.
        listener - the TailerListener to use.
      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener,
                      long delayMillis)
        Creates a Tailer for the given file, starting from the beginning.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener,
                      long delayMillis,
                      boolean end)
        Creates a Tailer for the given file, with a delay other than the default 1.0s.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener,
                      long delayMillis,
                      boolean end,
                      boolean reOpen)
        Creates a Tailer for the given file, with a delay other than the default 1.0s.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - if true, close and reopen the file between reading chunks
      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener,
                      long delayMillis,
                      boolean end,
                      int bufSize)
        Creates a Tailer for the given file, with a specified buffer size.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        bufSize - Buffer size
      • Tailer

        public Tailer​(java.io.File file,
                      TailerListener listener,
                      long delayMillis,
                      boolean end,
                      boolean reOpen,
                      int bufSize)
        Creates a Tailer for the given file, with a specified buffer size.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - if true, close and reopen the file between reading chunks
        bufSize - Buffer size
      • Tailer

        public Tailer​(java.io.File file,
                      java.nio.charset.Charset charset,
                      TailerListener listener,
                      long delayMillis,
                      boolean end,
                      boolean reOpen,
                      int bufSize)
        Creates a Tailer for the given file, with a specified buffer size.
        Parameters:
        file - the file to follow.
        charset - the Charset to be used for reading the file
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - if true, close and reopen the file between reading chunks
        bufSize - Buffer size
    • Method Detail

      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener,
                                    long delayMillis,
                                    boolean end,
                                    int bufSize)
        Creates and starts a Tailer for the given file.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        bufSize - buffer size.
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener,
                                    long delayMillis,
                                    boolean end,
                                    boolean reOpen,
                                    int bufSize)
        Creates and starts a Tailer for the given file.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - whether to close/reopen the file between chunks
        bufSize - buffer size.
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    java.nio.charset.Charset charset,
                                    TailerListener listener,
                                    long delayMillis,
                                    boolean end,
                                    boolean reOpen,
                                    int bufSize)
        Creates and starts a Tailer for the given file.
        Parameters:
        file - the file to follow.
        charset - the character set to use for reading the file
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - whether to close/reopen the file between chunks
        bufSize - buffer size.
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener,
                                    long delayMillis,
                                    boolean end)
        Creates and starts a Tailer for the given file with default buffer size.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener,
                                    long delayMillis,
                                    boolean end,
                                    boolean reOpen)
        Creates and starts a Tailer for the given file with default buffer size.
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        end - Set to true to tail from the end of the file, false to tail from the beginning of the file.
        reOpen - whether to close/reopen the file between chunks
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener,
                                    long delayMillis)
        Creates and starts a Tailer for the given file, starting at the beginning of the file
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        delayMillis - the delay between checks of the file for new content in milliseconds.
        Returns:
        The new tailer
      • create

        public static Tailer create​(java.io.File file,
                                    TailerListener listener)
        Creates and starts a Tailer for the given file, starting at the beginning of the file with the default delay of 1.0s
        Parameters:
        file - the file to follow.
        listener - the TailerListener to use.
        Returns:
        The new tailer
      • getFile

        public java.io.File getFile()
        Return the file.
        Returns:
        the file
      • getRun

        protected boolean getRun()
        Gets whether to keep on running.
        Returns:
        whether to keep on running.
        Since:
        2.5
      • getDelay

        public long getDelay()
        Return the delay in milliseconds.
        Returns:
        the delay in milliseconds.
      • run

        public void run()
        Follows changes in the file, calling the TailerListener's handle method for each new line.
        Specified by:
        run in interface java.lang.Runnable
      • stop

        public void stop()
        Allows the tailer to complete its current loop and return.
      • readLines

        private long readLines​(java.io.RandomAccessFile reader)
                        throws java.io.IOException
        Read new lines.
        Parameters:
        reader - The file to read
        Returns:
        The new position after the lines have been read
        Throws:
        java.io.IOException - if an I/O error occurs.