org.apache.commons.io.input
Class Tailer

java.lang.Object
  extended by org.apache.commons.io.input.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 Use 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 Use 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. Stop Tailing

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

      tailer.stop();
 

Since:
Commons IO 2.0
Version:
$Id: Tailer.java 1127854 2011-05-26 10:03:42Z sebb $
See Also:
TailerListener, TailerListenerAdapter

Field Summary
private  long delay
          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  TailerListener listener
          The listener to notify of events when tailing.
private  boolean run
          The tailer will run as long as this value is true.
 
Constructor Summary
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 delay)
          Creates a Tailer for the given file, starting from the beginning.
Tailer(java.io.File file, TailerListener listener, long delay, boolean end)
          Creates a Tailer for the given file, with a delay other than the default 1.0s.
 
Method Summary
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 delay)
          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 delay, boolean end)
          Creates and starts a Tailer for the given file.
 long getDelay()
          Return the delay.
 java.io.File getFile()
          Return the file.
private  java.lang.String readLine(java.io.RandomAccessFile reader)
          Version of readline() that returns null on EOF rather than a partial line.
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

file

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


delay

private final long delay
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.


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 delay)
Creates a Tailer for the given file, starting from the beginning.

Parameters:
file - the file to follow.
listener - the TailerListener to use.
delay - the delay between checks of the file for new content in milliseconds.

Tailer

public Tailer(java.io.File file,
              TailerListener listener,
              long delay,
              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.
delay - 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.
Method Detail

create

public static Tailer create(java.io.File file,
                            TailerListener listener,
                            long delay,
                            boolean end)
Creates and starts a Tailer for the given file.

Parameters:
file - the file to follow.
listener - the TailerListener to use.
delay - 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 delay)
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.
delay - 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

getDelay

public long getDelay()
Return the delay.

Returns:
the delay

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.

readLine

private java.lang.String readLine(java.io.RandomAccessFile reader)
                           throws java.io.IOException
Version of readline() that returns null on EOF rather than a partial line.

Parameters:
reader - the input file
Returns:
the line, or null if EOF reached before '\n' is seen.
Throws:
java.io.IOException - if an error occurs.


Copyright (c) 2002-2011 Apache Software Foundation