onInit() at your application's
* startup and onExit() at your application's shutdown and that's
* all there is to it. SingleAppInstance creates and locks a file
* within the startup directory so if anyone is to execute your application
* again the second onInit() call fails with a message.
* The onExit() method unlocks and deletes the file.
* If m_reportPopup is true, a popup window is displayed for the
* user to take action, else the user is informed via stderr.
* If you wish to change the look and feel of the popup window invoke
* SingleAppInstance after setting the look and feel inside your
* application. If you wish to translate the messages for this component create
* a new property file for your locale and place it inside
* /gr/zeus/ where the default
* "singleappinstance.properties" resides.
*
* @author Gregory Kotsaftis
* @since 1.05
*/
public final class SingleAppInstance {
/**
* Singleton.
*/
private static SingleAppInstance s_instance = null;
/**
* Instance file name.
*/
private static final String INSTANCE_FILENAME = "INSTANCE.RUN";
/**
* Used to create the file.
*/
private File m_file = null;
/**
* Used to read and write the file.
*/
private FileChannel m_channel = null;
/**
* Used to lock the temporary file.
*/
private FileLock m_lock = null;
/**
* Check to report errors via a popup if true or
* via stderr if false.
*/
private boolean m_reportPopup = true;
/**
* File lock error title.
*/
private static final String m_fileLockErrorTitle = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileLockErrorTitle");
/**
* File lock error message 1.
*/
private static final String m_fileLockErrorMsg1 = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileLockErrorMsg1");
/**
* File lock error message 2.
*/
private static final String m_fileLockErrorMsg2 = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileLockErrorMsg2");
/**
* File delete error title.
*/
private static final String m_fileDeleteErrorTitle =
ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileDeleteErrorTitle");
/**
* File delete error message 1.
*/
private static final String m_fileDeleteErrorMsg1 =
ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileDeleteErrorMsg1");
/**
* File delete error message 2.
*/
private static final String m_fileDeleteErrorMsg2 =
ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileDeleteErrorMsg2");
/**
* File exists title.
*/
private static final String m_fileExistsTitle = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileExistsTitle");
/**
* File exists error message 1.
*/
private static final String m_fileExistsMsg1 = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileExistsMsg1");
/**
* File exists error message 2.
*/
private static final String m_fileExistsMsg2 = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileExistsMsg2");
/**
* File exists error message 3.
*/
private static final String m_fileExistsMsg3 = ResourceBundle.getBundle(
"gr/zeus/res/singleappinstance").getString("fileExistsMsg3");
/**
* This method returns the single instance of this class.
*
* @return The single instance of this class. */ public synchronized static SingleAppInstance getInstance() { // lazy instantiation if( s_instance==null ) { s_instance = new SingleAppInstance(); } return( s_instance ); } /** * This method returns the single instance of this class. * Uses the filename parameter instead of default filename. *
* @param filename The filename to create and lock, should be unique and * within current folder. *
* @return The single instance of this class.
*/
public synchronized static SingleAppInstance getInstance(String filename)
{
// lazy instantiation
if( s_instance==null )
{
s_instance = new SingleAppInstance( filename );
}
return( s_instance );
}
/**
* Creates a file and obtains a lock. If the file exists or
* there is any error creating it this method invokes
* System.exit(). Should be invoked ONCE
* inside main() in your application.
*/
public synchronized void onInit()
{
// if file already exists...
if( m_file.exists() )
{
// notify user and ask for instructions...
if( inform_user()==false )
{
System.exit( 1 );
}
// ok, he is sure. try to delete the old file.
if( force_delete_file()==false )
{
System.exit( 2 );
}
}
// try to create and lock the file.
if( lock_file()==false )
{
System.exit( 3 );
}
}
/**
* Release the file lock and delete the file.
* Should be invoked ONCE just before calling
* System.exit() on your application.
*/
public synchronized void onExit()
{
try
{
// Release the lock, close and delete the file
m_lock.release();
m_channel.close();
m_file.delete();
}
catch(Exception e)
{
// not much to do here, since the application is possibly exiting...
e.printStackTrace();
}
}
/**
* Gets whether to report via a popup or via stderr.
*
* @return If true, a popup window is displayed,
* else the user is informed via stderr.
*/
public boolean getReportPopup()
{
return( m_reportPopup );
}
/**
* Sets whether to report via a popup or via stderr.
*
* @param f If true, via a popup window,
* else via stderr.
*/
public synchronized void setReportPopup(boolean f)
{
m_reportPopup = f;
}
/**
* Private constructor.
*/
private SingleAppInstance()
{
m_file = new File( INSTANCE_FILENAME );
}
/**
* Private constructor.
*
* @param filename The filename to create and lock, should be unique and * within current folder. */ private SingleAppInstance(String filename) { m_file = new File( filename ); } /** * Reports a lock error. *
* @param s The error message. */ private void report_lock_error(String s) { String msg = m_fileLockErrorMsg1 + m_file.getAbsolutePath() + m_fileLockErrorMsg2 + s; String title = m_fileLockErrorTitle; if( m_reportPopup ) { JOptionPane.showMessageDialog(null, msg, title, JOptionPane.ERROR_MESSAGE); } else { System.err.println( msg ); } } /** * Reports a delete error. *
* @param s The error message. */ private void report_delete_error(String s) { String msg = m_fileDeleteErrorMsg1 + m_file.getAbsolutePath(); if( s!=null ) { msg += m_fileDeleteErrorMsg2 + s; } String title = m_fileDeleteErrorTitle; if( m_reportPopup ) { JOptionPane.showMessageDialog(null, msg, title, JOptionPane.ERROR_MESSAGE); } else { System.err.println( msg ); } } /** * Creates and locks the file. *
* @return true if file is locked,
* false otherwise.
*/
private boolean lock_file()
{
try
{
// create the file and obtain a lock to it.
// this way nobody can delete this file as long as this
// application is running!
m_channel = new RandomAccessFile(m_file, "rw").getChannel();
m_lock = m_channel.lock();
return( true );
}
catch(Exception ex)
{
report_lock_error( ex.getMessage() );
return( false );
}
}
/**
* Force deletion of the file.
*
* @return true if file is deleted,
* false otherwise.
*/
private boolean force_delete_file()
{
try
{
boolean deleted = m_file.delete();
if( !deleted )
{
report_delete_error( null );
}
return( deleted );
}
catch(Exception ex)
{
report_delete_error( ex.getMessage() );
return( false );
}
}
/**
* Informs the user that the file exists.
*
* @return true if user is informed,
* false otherwise.
*/
private boolean inform_user()
{
String msg_gui = m_fileExistsMsg1 + m_fileExistsMsg2;
String msg_txt = m_fileExistsMsg1 + m_fileExistsMsg3 +
m_file.getAbsolutePath();
String title = m_fileExistsTitle;
if( m_reportPopup )
{
int res = JOptionPane.showConfirmDialog(null, msg_gui, title,
JOptionPane.OK_CANCEL_OPTION,
JOptionPane.WARNING_MESSAGE);
return( res==0 ); // if YES return true
}
else
{
System.err.println( msg_txt );
return( false );
}
}
}