org.apache.commons.io.input

Class Tailer

java.lang.Object

org.apache.commons.io.input.Tailer

All Implemented Interfaces:

AutoCloseable, Runnable

public class Tailer
extends Object
implements Runnable, AutoCloseable

Simple implementation of the Unix "tail -f" functionality.

To build an instance, use Tailer.Builder.

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 a Tailer.Builder
• Using an Executor
• Using a Thread

An example of each is shown below.

2.1 Using a Builder

 TailerListener listener = new MyTailerListener();
 Tailer tailer = Tailer.builder()
   .setFile(file)
   .setTailerListener(listener)
   .setDelayDuration(delay)
   .get();
 

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.

See Also:

Tailer.Builder, TailerListener, TailerListenerAdapter

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Tailer.Builder Builds a new Tailer.
static interface	Tailer.RandomAccessResourceBridge Bridges access to a resource for random access, normally a file.
static interface	Tailer.Tailable A tailable resource like a file.

Method Summary

Modifier and Type	Method and Description
static Tailer.Builder	builder() Constructs a new Tailer.Builder.
void	close() Requests the tailer to complete its current loop and return.
java.time.Duration	getDelayDuration() Gets the delay Duration.
File	getFile() Gets the file.
protected boolean	getRun() Gets whether to keep on running.
Tailer.Tailable	getTailable() Gets the Tailable.
void	run() Follows changes in the file, calling TailerListener.handle(String) with each new line.

Methods inherited from class java.lang.Object

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

Method Detail

builder

public static Tailer.Builder builder()

Constructs a new Tailer.Builder.

Returns:

Creates a new Tailer.Builder.

close

public void close()

Requests the tailer to complete its current loop and return.

Specified by:

close in interface AutoCloseable

getDelayDuration

public java.time.Duration getDelayDuration()

Gets the delay Duration.

Returns:

the delay Duration.

getFile

public File getFile()

Gets the file.

Returns:

the file

Throws:

IllegalStateException - if constructed using a user provided Tailer.Tailable implementation

getRun

protected boolean getRun()

Gets whether to keep on running.

Returns:

whether to keep on running.

getTailable

public Tailer.Tailable getTailable()

Gets the Tailable.

Returns:

the Tailable

run

public void run()

Follows changes in the file, calling TailerListener.handle(String) with each new line.

Specified by:

run in interface Runnable