org.apache.commons.io.input

Class Tailer

java.lang.Object

org.apache.commons.io.input.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:

• Using one of the static helper methods:
  • create(File, TailerListener)
  • create(File, TailerListener, long)
  • create(File, TailerListener, long, boolean)
• Using an Executor
• Using an Thread

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.

Method Summary

Modifier and Type	Method and Description
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.
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
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
static Tailer	create(File file, TailerListener listener, long delayMillis, boolean end) Creates and starts a Tailer for the given file with default buffer size.
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.
static Tailer	create(File file, TailerListener listener, long delayMillis, boolean end, boolean reOpen, int bufSize) Creates and starts a Tailer for the given file.
static Tailer	create(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.
File	getFile() Return the file.
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

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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

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.