Logging ...

[Jon Camilleri]

"It is important to note that the Logger returned by one of the getLogger factory methods may be garbage collected at any time if a strong reference to the Logger is not kept."

Sourced from here.


1. Can you confirm that the following code holds a strong reference to the Logger, and, point out any issues where the Garbage Collector Is it possible to tweak the code and use a WeakReference, or would it be an example of overdoing it?
might trip up?
2. I would also like to know whether I can control the size of the file before another file gets created within the rotation sequence of logs.
Within my environment (WinXP/JDK 1.6) the log files are written to c:\documents and settings\%windows user name%
3. How does the code snippet below automatically read the file name (line 121)? How does the parameter reading
mechanism work for say {0}, {1}, {2} etc.?
4. How can I create some code that controls when the logging is switched off and on in a similar fashion of C++ macros.
5. Why does the programmer pass the 2nd parameter (line 87) as "<init>", since this is not written to the log file?
6. Is it possible to update the code, using Reflection classes as parameters to Logger.logp() - see Related link (2) for basic syntax example?
...
logger.logp(Level.INFO, this.getClass().forName(), "ImageViewerFrame()", "test logger"); //this is dummy non-working code
...

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.logging.*;
import javax.swing.*;

/**
 * A modification of the image viewer program that logs various events.
 * @version 1.02 2007-05-31
 * @author Cay Horstmann
 */
public class LoggingImageViewer
{
   public static void main(String[] args)
   {
      if (System.getProperty("java.util.logging.config.class") == null
            && System.getProperty("java.util.logging.config.file") == null)
      {
         try
         {
            Logger.getLogger("com.horstmann.corejava").setLevel(Level.ALL);
            final int LOG_ROTATION_COUNT = 10;
            Handler handler = new FileHandler("%h/LoggingImageViewer.log", 0, LOG_ROTATION_COUNT);
            Logger.getLogger("com.horstmann.corejava").addHandler(handler);
         }
         catch (IOException e)
         {
            Logger.getLogger("com.horstmann.corejava").log(Level.SEVERE,
                  "Can't create log file handler", e);
         }
      }

      EventQueue.invokeLater(new Runnable()
         {
            public void run()
            {
               Handler windowHandler = new WindowHandler();
               windowHandler.setLevel(Level.ALL);
               Logger.getLogger("com.horstmann.corejava").addHandler(windowHandler);

               JFrame frame = new ImageViewerFrame();
               frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

               Logger.getLogger("com.horstmann.corejava").fine("Showing frame");
               frame.setVisible(true);
            }
         });
   }
}

/**
 * The frame that shows the image.
 */
class ImageViewerFrame extends JFrame
{
   public ImageViewerFrame()
   {
      logger.entering("ImageViewerFrame", "<init>");
      setTitle("LoggingImageViewer");
      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

      // set up menu bar
      JMenuBar menuBar = new JMenuBar();
      setJMenuBar(menuBar);

      JMenu menu = new JMenu("File");
      menuBar.add(menu);

      JMenuItem openItem = new JMenuItem("Open");
      menu.add(openItem);
      openItem.addActionListener(new FileOpenListener());

      JMenuItem exitItem = new JMenuItem("Exit");
      menu.add(exitItem);
      exitItem.addActionListener(new ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               logger.fine("Exiting.");
               System.exit(0);
            }
         });

      // use a label to display the images
      label = new JLabel();
      add(label);
      logger.exiting("ImageViewerFrame", "<init>");
   }

   private class FileOpenListener implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         logger.entering("ImageViewerFrame.FileOpenListener", "actionPerformed", event);

         // set up file chooser
         JFileChooser chooser = new JFileChooser();
         chooser.setCurrentDirectory(new File("."));

         // accept all files ending with .gif
         chooser.setFileFilter(new javax.swing.filechooser.FileFilter()
            {
               public boolean accept(File f)
               {
                  return f.getName().toLowerCase().endsWith(".gif") || f.isDirectory();
               }

               public String getDescription()
               {
                  return "GIF Images";
               }
            });

         // show file chooser dialog
         int r = chooser.showOpenDialog(ImageViewerFrame.this);

         // if image file accepted, set it as icon of the label
         if (r == JFileChooser.APPROVE_OPTION)
         {
            String name = chooser.getSelectedFile().getPath();
            logger.log(Level.FINE, "Reading file {0}", name); //writes the path and name of the file to the logger 
            label.setIcon(new ImageIcon(name));
         }
         else logger.fine("File open dialog canceled.");
         logger.exiting("ImageViewerFrame.FileOpenListener", "actionPerformed");
      }
   }

   private JLabel label;
   private static Logger logger = Logger.getLogger("com.horstmann.corejava");
   private static final int DEFAULT_WIDTH = 300;
   private static final int DEFAULT_HEIGHT = 400;   
}

/**
 * A handler for displaying log records in a window.
 */
class WindowHandler extends StreamHandler
{
   public WindowHandler()
   {
      frame = new JFrame();
      final JTextArea output = new JTextArea();
      output.setEditable(false);
      frame.setSize(200, 200);
      frame.add(new JScrollPane(output));
      frame.setFocusableWindowState(false);
      frame.setVisible(true);
      setOutputStream(new OutputStream()
         {
            public void write(int b)
            {
            } // not called

            public void write(byte[] b, int off, int len)
            {
               output.append(new String(b, off, len));
            }
         });
   }

   public void publish(LogRecord record)
   {
      if (!frame.isVisible()) return;
      super.publish(record);
      flush();
   }

   private JFrame frame;
}

Sourced from Core Java Vol.I (8th Ed) P. 584-588 Listing 11.2


Related links
1. E. Nicholas, Understanding weak references
2. Logger logp() example

Log file at C:\Documents and Settings\Jon\LoggingImageViewer.log.0
<?xml version="1.0" encoding="windows-1252" standalone="no"?>
<!DOCTYPE log SYSTEM "logger.dtd">
<log>
<record>
<date>2011-06-05T12:23:56</date>
<millis>1307269436593</millis>
<sequence>0</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame</class>
<method><init></method>
<thread>10</thread>
<message>ENTRY</message>
</record>
<record>
<date>2011-06-05T12:23:56</date>
<millis>1307269436625</millis>
<sequence>1</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame</class>
<method><init></method>
<thread>10</thread>
<message>RETURN</message>
</record>
<record>
<date>2011-06-05T12:23:56</date>
<millis>1307269436625</millis>
<sequence>2</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINE</level>
<class>LoggingImageViewer$1</class>
<method>run</method>
<thread>10</thread>
<message>Showing frame</message>
</record>
<record>
<date>2011-06-05T12:31:19</date>
<millis>1307269879671</millis>
<sequence>3</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame.FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>ENTRY java.awt.event.ActionEvent[ACTION_PERFORMED,cmd=Open,when=1307269879671,modifiers=Button1] on javax.swing.JMenuItem[,1,3,51x21,invalid,alignmentX=0.0,alignmentY=0.0,border=javax.swing.plaf.metal.MetalBorders$MenuItemBorder@131f71a,flags=264,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=true,paintFocus=false,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Open]</message>
</record>
<record>
<date>2011-06-05T12:31:40</date>
<millis>1307269900437</millis>
<sequence>4</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINE</level>
<class>ImageViewerFrame$FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>Reading file C:\Documents and Settings\Jon\My Documents\My Archives\My Pictures\chat\rita26-3.jpg</message>
</record>
<record>
<date>2011-06-05T12:31:40</date>
<millis>1307269900515</millis>
<sequence>5</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame.FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>RETURN</message>
</record>
<record>
<date>2011-06-05T12:31:43</date>
<millis>1307269903390</millis>
<sequence>6</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame.FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>ENTRY java.awt.event.ActionEvent[ACTION_PERFORMED,cmd=Open,when=1307269903390,modifiers=Button1] on javax.swing.JMenuItem[,1,3,51x21,invalid,alignmentX=0.0,alignmentY=0.0,border=javax.swing.plaf.metal.MetalBorders$MenuItemBorder@131f71a,flags=264,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=2,bottom=2,right=2],paintBorder=true,paintFocus=false,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Open]</message>
</record>
<record>
<date>2011-06-05T12:32:04</date>
<millis>1307269924000</millis>
<sequence>7</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINE</level>
<class>ImageViewerFrame$FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>Reading file C:\Documents and Settings\Jon\My Documents\My Archives\New car (july 2010)\uktomalta.com - Mazda 3 1.6D TS Hatchback (2008) - 21.07.2010.pdf</message>
</record>
<record>
<date>2011-06-05T12:32:04</date>
<millis>1307269924109</millis>
<sequence>8</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINER</level>
<class>ImageViewerFrame.FileOpenListener</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>RETURN</message>
</record>
<record>
<date>2011-06-05T12:32:07</date>
<millis>1307269927187</millis>
<sequence>9</sequence>
<logger>com.horstmann.corejava</logger>
<level>FINE</level>
<class>ImageViewerFrame$1</class>
<method>actionPerformed</method>
<thread>10</thread>
<message>Exiting.</message>
</record>
</log>