Frontend Logging with JavaFX and Log4j 2

Although I'm developing Java EE applications with HTML5, I sometimes have to build Java SE applications with a Frontend. I've used Swing or AWT in the past. But since JavaFX 2.0 get lost of that awful JavaFX Script, JavaFX is my weapon of choice. Recently I wrote a multithreaded applications that needs to inform the user of some working results. I guess I was some kind of blue-eyed when I wrote this "log" function:

public static void guiLog(String logstring){  

and used it like that:

Platform.runLater(() -> Controller.guiLog("Hello World :)"));  

I still don't know if that would've worked reliable in a single thread application, but in my case the GUI hangs after 30-45 seconds while using 8 threads. And to be honest: That kind of logging didn't feel correct...

So I took a look at Log4j 2 appenders and I was not disappointed. Implementing your own appender, in my case a TextArea appender is quite easy.

import javafx.application.Platform;  
import javafx.scene.control.TextArea;  
import org.apache.logging.log4j.core.Filter;  
import org.apache.logging.log4j.core.Layout;  
import org.apache.logging.log4j.core.LogEvent;  
import org.apache.logging.log4j.core.appender.AbstractAppender;  
import org.apache.logging.log4j.core.config.plugins.Plugin;  
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;  
import org.apache.logging.log4j.core.config.plugins.PluginElement;  
import org.apache.logging.log4j.core.config.plugins.PluginFactory;  
import org.apache.logging.log4j.core.layout.PatternLayout;

import java.util.concurrent.locks.Lock;  
import java.util.concurrent.locks.ReadWriteLock;  
import java.util.concurrent.locks.ReentrantReadWriteLock;

 * TextAreaAppender for Log4j 2
    name = "TextAreaAppender",
    category = "Core",
    elementType = "appender",
    printObject = true)
public final class TextAreaAppender extends AbstractAppender {

  private static TextArea textArea;

  private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
  private final Lock readLock = rwLock.readLock();

  protected TextAreaAppender(String name, Filter filter,
                             Layout<? extends Serializable> layout,
                             final boolean ignoreExceptions) {
    super(name, filter, layout, ignoreExceptions);

   * This method is where the appender does the work.
   * @param event Log event with log data
  public void append(LogEvent event) {

    final String message = new String(getLayout().toByteArray(event));

    // append log text to TextArea
    try {
      Platform.runLater(() -> {
        try {
          if (textArea != null) {
            if (textArea.getText().length() == 0) {
            } else {
        } catch (final Throwable t) {
          System.out.println("Error while append to TextArea: "
              + t.getMessage());
    } catch (final IllegalStateException ex) {

    } finally {

   * Factory method. Log4j will parse the configuration and call this factory 
   * method to construct the appender with
   * the configured attributes.
   * @param name   Name of appender
   * @param layout Log layout of appender
   * @param filter Filter for appender
   * @return The TextAreaAppender
  public static TextAreaAppender createAppender(
      @PluginAttribute("name") String name,
      @PluginElement("Layout") Layout<? extends Serializable> layout,
      @PluginElement("Filter") final Filter filter) {
    if (name == null) {
      LOGGER.error("No name provided for TextAreaAppender");
      return null;
    if (layout == null) {
      layout = PatternLayout.createDefaultLayout();
    return new TextAreaAppender(name, filter, layout, true);

   * Set TextArea to append
   * @param textArea TextArea to append
  public static void setTextArea(TextArea textArea) {
    TextAreaAppender.textArea = textArea;

The only thing left is to announce the appender in the Log4j configuration

<?xml version="1.0" encoding="UTF-8"?>  
<Configuration status="INFO">  
        <TextAreaAppender name="JavaFXLogger">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %c{1}:%L - %m%n"/>
        <Root level="debug">
            <AppenderRef ref="JavaFXLogger"/>

Happy logging ;) !