org.apache.commons.io.input

Class Tailer

  • All Implemented Interfaces:
    Runnable

    public class Tailer
    extends Object
    implements 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
    • Constructor Summary

      Constructors  
      Constructor and Description
      Tailer(File file, 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(File file, TailerListener listener)
      Creates a Tailer for the given file, starting from the beginning, with the default delay of 1.0s.
      Tailer(File file, TailerListener listener, long delayMillis)
      Creates a Tailer for the given file, starting from the beginning.
      Tailer(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(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(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(File file, TailerListener listener, long delayMillis, boolean end, int bufSize)
      Creates a Tailer for the given file, with a specified buffer size.
    • Constructor Detail

      • Tailer

        public Tailer(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(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(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(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(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(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(File file,
                      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(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(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(File file,
                                    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(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(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(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(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 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  Runnable
      • stop

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

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