これはやや古いですが、私はメカニズムを使用しており、かなりうまく機能しています。
編集: リンクは機能しなくなりましたが、インターネット アーカイブで見つけました
https://web.archive.org/web/20160510001134/http://www.informit.com/guides/content.aspx?g=java&seqNum=226
トリックは、を使用しjava.io.RandomAccessFile、ファイルの長さが現在のファイル位置よりも大きいかどうかを定期的に確認することです。そうであれば、データを読み取ります。長さを打ったら、待ってください。洗う、すすぐ、繰り返す。
新しいリンクが機能しなくなった場合に備えて、コードをコピーしました
package com.javasrc.tuning.agent.logfile;
import java.io.*;
import java.util.*;
/**
* A log file tailer is designed to monitor a log file and send notifications
* when new lines are added to the log file. This class has a notification
* strategy similar to a SAX parser: implement the LogFileTailerListener interface,
* create a LogFileTailer to tail your log file, add yourself as a listener, and
* start the LogFileTailer. It is your job to interpret the results, build meaningful
* sets of data, etc. This tailer simply fires notifications containing new log file lines,
* one at a time.
*/
public class LogFileTailer extends Thread
{
/**
* How frequently to check for file changes; defaults to 5 seconds
*/
private long sampleInterval = 5000;
/**
* The log file to tail
*/
private File logfile;
/**
* Defines whether the log file tailer should include the entire contents
* of the exising log file or tail from the end of the file when the tailer starts
*/
private boolean startAtBeginning = false;
/**
* Is the tailer currently tailing?
*/
private boolean tailing = false;
/**
* Set of listeners
*/
private Set listeners = new HashSet();
/**
* Creates a new log file tailer that tails an existing file and checks the file for
* updates every 5000ms
*/
public LogFileTailer( File file )
{
this.logfile = file;
}
/**
* Creates a new log file tailer
*
* @param file The file to tail
* @param sampleInterval How often to check for updates to the log file (default = 5000ms)
* @param startAtBeginning Should the tailer simply tail or should it process the entire
* file and continue tailing (true) or simply start tailing from the
* end of the file
*/
public LogFileTailer( File file, long sampleInterval, boolean startAtBeginning )
{
this.logfile = file;
this.sampleInterval = sampleInterval;
}
public void addLogFileTailerListener( LogFileTailerListener l )
{
this.listeners.add( l );
}
public void removeLogFileTailerListener( LogFileTailerListener l )
{
this.listeners.remove( l );
}
protected void fireNewLogFileLine( String line )
{
for( Iterator i=this.listeners.iterator(); i.hasNext(); )
{
LogFileTailerListener l = ( LogFileTailerListener )i.next();
l.newLogFileLine( line );
}
}
public void stopTailing()
{
this.tailing = false;
}
public void run()
{
// The file pointer keeps track of where we are in the file
long filePointer = 0;
// Determine start point
if( this.startAtBeginning )
{
filePointer = 0;
}
else
{
filePointer = this.logfile.length();
}
try
{
// Start tailing
this.tailing = true;
RandomAccessFile file = new RandomAccessFile( logfile, "r" );
while( this.tailing )
{
try
{
// Compare the length of the file to the file pointer
long fileLength = this.logfile.length();
if( fileLength < filePointer )
{
// Log file must have been rotated or deleted;
// reopen the file and reset the file pointer
file = new RandomAccessFile( logfile, "r" );
filePointer = 0;
}
if( fileLength > filePointer )
{
// There is data to read
file.seek( filePointer );
String line = file.readLine();
while( line != null )
{
this.fireNewLogFileLine( line );
line = file.readLine();
}
filePointer = file.getFilePointer();
}
// Sleep for the specified interval
sleep( this.sampleInterval );
}
catch( Exception e )
{
}
}
// Close the file that we are tailing
file.close();
}
catch( Exception e )
{
e.printStackTrace();
}
}
}