Need help for Log4j 1.2 used in a standalone application

[Alex Yx Ng]

Hi guys,

I am building a standalone application and I'd like to use log4j 1.2 to append logs from different classes to a JTextarea, some of you might say this is not ideal because this would couple the UI and low level logging together, but this application is simply a practice, and I'd like to try all kinds of approach.

I have created some test class outside the application just to test log4j before I put it into the actual app, these are the codes what I have done,

UI class

public class Log4j2Example {
	class LogModel extends AbstractTableModel{

		@Override
		public int getColumnCount() {
			// TODO Auto-generated method stub
			return 1;
		}

		@Override
		public int getRowCount() {
			// TODO Auto-generated method stub
			return 0;
		}

		@Override
		public Object getValueAt(int rowIndex, int columnIndex) {
			// TODO Auto-generated method stub
			switch(columnIndex){
				case 0: return null;
				default: return null;
			}
		}
		
	}
	private final JTextArea textarea = new JTextArea();
	private final LogModel model = new LogModel();
	private final JTable table = new JTable(model);
	static Log4j2Example INSTANCE = new Log4j2Example();
	JFrame frame = new JFrame();
	
	void run(){
		frame.setLayout(new BorderLayout());
		table.setBorder(new TitledBorder("Table"));
		textarea.setBorder(new TitledBorder("Text Area"));
		table.setPreferredSize(new Dimension(100, 300));
		textarea.setEditable(false);
		
		frame.add(table, BorderLayout.NORTH);
		frame.add(new JScrollPane(textarea));
		
		frame.setVisible(true);
		frame.setSize(400, 400);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
	public JTextArea getJTextArea(){
		return this.textarea;
	}

	static final Logger logger = Logger.getLogger(Log4j2Example.class.getName());
	public static void main(String[] args) {
		INSTANCE.run();
		PropertyConfigurator.configure("resources/log4j.properties");
		
		JTextAreaAppender jtaa = new JTextAreaAppender(INSTANCE.getJTextArea());
		logger.addAppender(jtaa);
	
		logger.warn("first");
		logger.warn("second");
		logger.warn("third");
		logger.debug("Sample debug message");
		logger.info("Sample info message");
		logger.warn("Sample warn message");
		logger.fatal("Sample fatal message");

		logger.trace("fourth shouldn't be printed");

		Hello hello = new Hello();
		if (!hello.callMe()) {
			logger.error("Ohh!Failed!");
		}		
		
	}
}

Hello class

public class Hello {
//  static final Logger logger = LogManager.getLogger(Hello.class.getName());
  static final Logger logger = Logger.getLogger(Hello.class.getName());
  public boolean callMe() {
//    logger.entry();
    logger.error("Inside Hello Logger!");
    return false; //logger.exit(false);
  }
}

The custom appender

public class JTextAreaAppender extends AppenderSkeleton
    implements DocumentListener
{
    //--------------------------------------------------------------------------
    // Fields
    //--------------------------------------------------------------------------

    /**
     * Text area that logging statements are directed to.
     */
    private JTextArea textArea_;

    /**
     * Layout for logging statements.
     */
    private PatternLayout layout_;

    //--------------------------------------------------------------------------
    // Constructors
    //--------------------------------------------------------------------------
    public JTextAreaAppender(){
    	
    }
    /**
     * Creates a new text area appender.
     *
     * @param textArea Text area to connect the appender to.
     */
    public JTextAreaAppender(JTextArea textArea)
    {
        textArea_ = textArea;
        textArea_.getDocument().addDocumentListener(this);
        layout_ = new PatternLayout("%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n");
    }

    //--------------------------------------------------------------------------
    // Public
    //--------------------------------------------------------------------------

    /**
     * Returns the text area.
     *
     * @return JTextArea
     */
    public JTextArea getTextArea()
    {
        return textArea_;
    }

    //--------------------------------------------------------------------------
    // Overrides org.apache.log4j.AppenderSkeleton
    //--------------------------------------------------------------------------

    /**
     * @see org.apache.log4j.AppenderSkeleton#append(
     *      org.apache.log4j.spi.LoggingEvent)
     */
    public void append(LoggingEvent loggingEvent)
    {
    	textArea_.append(layout_.format(loggingEvent));
    }


    /**
     * @see org.apache.log4j.Appender#requiresLayout()
     */
    public boolean requiresLayout()
    {
        return false;
    }


    /**
     * @see org.apache.log4j.Appender#close()
     */
    public void close()
    {
    }

    //--------------------------------------------------------------------------
    // javax.swing.event.DocumentListener Interface
    //--------------------------------------------------------------------------

    /**
     * @see javax.swing.event.DocumentListener#changedUpdate(
     *      javax.swing.event.DocumentEvent)
     */
    public void changedUpdate(DocumentEvent event)
    {
    }


    /**
     * @see javax.swing.event.DocumentListener#removeUpdate(
     *      javax.swing.event.DocumentEvent)
     */
    public void removeUpdate(DocumentEvent event)
    {
    }


    /**
     * Sets the caret position to the end of the text in the text component
     * whenever it is updated.
     *
     * @see javax.swing.event.DocumentListener#insertUpdate(
     *      javax.swing.event.DocumentEvent)
     */
    public void insertUpdate(DocumentEvent event)
    {
    	textArea_.setCaretPosition(textArea_.getDocument().getLength());
    }
}

log4j.properties file which I have put under resources folder, same level as src folder

log4j.rootLogger=INFO, stdout, textarea # Direct log messages to a JTextArea log4j.appender.textarea=testing.JTextAreaAppender log4j.appender.textarea.layout=org.apache.log4j.PatternLayout log4j.appender.textarea.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n # Direct log messages to stdout log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target=System.out log4j.appender.stdout.layout=org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

problems I have now and I dont know how to resolve as following,

If I run the UI class like these, I would get a NullPointException and only the first log would be logged both into the text area and eclipse console

The PropertyConfigurator doesnot configure layout properly if I changed the requiresLayout method in JTextArea to return true, it'd be null, I believe that'd be the reason I am getting NPE, but I am so confused about how I could resolve this

If I changed this line "log4j.rootLogger=INFO, stdout, textarea" in the property file to "log4j.rootLogger=textarea", all testing log can be appended to textarea but the console prompts the following error msg - log4j:WARN No appenders could be found for logger (testing.Hello).
log4j:WARN Please initialize the log4j system properly.

If I add the Help logger to configuration file as changing the line to "log4j.rootLogger=INFO, stdout, textarea, Help" then add all layout and ConversionPattern lines for logger Help, it gives me NPE

What I want to achieve is, all logs in different classes should be able to be appended to textarea properly, using log4j.properties for configuration. I have been trying for days, since I work long hours during the day and only be able to work on my project at nights. Any help for these matters would be greatly appreciated.

[Alex Yx Ng]

I'm stuck.
Nobody could give me some help?

[Arianna Microchip]

Hello!

You don't modify your log4j.properties!
If you must change your pattern layout, you modify

(line 33)   layout_ = new PatternLayout("%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n");