Alex Yx Ng

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

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.