Write Log4J to jTextArea

Question

I'm an inexperienced Java developer writing an application that is handling a backup.

My application opens a gui (StepTwoBackup written using NetBeans Template), which gathers some information from the user, then when I press on the "Next" button, the gui passes these information to an object (BackupRestore which is logging all the operation using Log4J), and then opens another window (StepThreeBackup) and passes the object to it.

In this new window(StepThreeBackup), I automatically launch a method on the object passed (BackupRestore.execute()) which performs the backup. In this last window (StepThreeBackup) I created a JTextArea where I would like to show the output of the Log4J (which currently writes to a log file and outputs to console).

Is there a way to do this? I've read that I should use an appender, but cannot figure out how to do this correctly.

For the time being I've created the following entry in my working Log4J property file:

<appender name="guiAppender" class="BackupAppGui.StatusMessageAppender">
<param name="Threshold" value="INFO" />
<layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%d{dd MMM yyyy HH:mm:ss} %5p %c{1} - %m%n"/>
</layout>
</appender>

Then the following Class in my Package (following another post):

package BackupAppGui;

/**
 *
 * @author MSTPA
 */
import javax.swing.JTextArea;
import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.Level;
import org.apache.log4j.spi.LoggingEvent;


public class StatusMessageAppender extends AppenderSkeleton {
    private final JTextArea jTextA;

    public StatusMessageAppender() {
        jTextA = StepThreeBackup.getJTextA();
    }
    protected void append(LoggingEvent event) 
    {
        if(event.getLevel().equals(Level.INFO)){
        jTextA.append(event.getMessage().toString());
        }
    }
    public void close() 
    {
    }
    public boolean requiresLayout() 
    {
        return false;
    }
}

But nothing is written to the jTextArea.

What am I doing wrong? Can someone help me solving this? Thank you for all the help you can give me.

Answer 1

You need to make sure that the instance of JTextArea is not null. Yoy can try adding the appender programmatically (e.g. in the constructor of StepThreeBackup after create the components):

StatusMessageAppender appender = new StatusMessageAppender();
LogManager.getRootLogger().addAppender(appender);

Don't forget delete the entry in the log4j.xml file.