Most efficient way to log messages to JavaFX TextArea via threads with simple custom logging frameworks


I have a simple custom logging framework like this:

package something;

import javafx.scene.control.TextArea;

public class MyLogger {
    public final TextArea textArea;

    private boolean verboseMode = false;
    private boolean debugMode = false;

    public MyLogger(final TextArea textArea) {
        this.textArea = textArea;

    public MyLogger setVerboseMode(boolean value) {
        verboseMode = value;
        return this;

    public MyLogger setDebugMode(boolean value) {
        debugMode = value;
        return this;

    public boolean writeMessage(String msg) {
        return true;

    public boolean logMessage(String msg) {
        return writeMessage(msg + "\n");

    public boolean logWarning(String msg) {
        return writeMessage("Warning: " + msg + "\n");

    public boolean logError(String msg) {
        return writeMessage("Error: " + msg + "\n");

    public boolean logVerbose(String msg) {
        return verboseMode ? writeMessage(msg + "\n") : true;

    public boolean logDebug(String msg) {
        return debugMode ? writeMessage("[DEBUG] " + msg + "\n") : true;

Now what I want to do is to extend it so that it would be able to properly handle logging of messages via threads. I have tried solutions like using message queues with an AnimationTimer. It works but it slows the GUI down.

I also tried using a scheduled service which runs a thread that reads messages from the message queue, concatenates them, and appends them to TextArea (textArea.appendText(stringBuilder.toString())). The problem is that the TextArea control goes unstable i.e. you had to highlight all texts with Ctrl-A and try resizing the window to make them appear well. There are also some of them being displayed in a light-blue background not sure what's causing it. My first guess here is that the race condition may not be allowing the control to update itself well from the new strings. It is also worth noting that the textarea is wrapped around a ScrollPane so it adds the confusion if TextArea is actually the one having the problem or ScrollPane. I have to mention as well that this approach doesn't make the TextArea control update itself with messages quickly.

I thought about binding TextArea.TextProperty() to something that does the update but I'm not sure how I would do that properly knowing that the gatherer of messages (be it by a service or a lone thread) would still be running different from the GUI thread.

I have tried to look up on other known logging framework solutions like log4j and some stuffs referred here but none of them seems to give an apparent approach to logging via threads to TextArea. I also don't like the idea of building my logging system on top of them as they already have their pre-defined mechanisms like logging level, etc.

I've seen this as well. It implies using SwingUtilities.invokeLater(Runnable) to update the control but I already tried a similar approach using javafx.application.platform.runLater() which gets executed on the worker thread. I'm not sure if there was something I was doing wrong but it just hangs. It can produce messages but not when they're aggressive enough. I estimate that the worker thread running in a purely synchronous fashion can actually produce about 20 or more average lines per second and more when it's in debug mode. A possible workaround would be to add message queueing to it as well but that doesn't make sense anymore.

5/23/2017 10:31:28 AM

Accepted Answer


.root {
    -fx-padding: 10px;

.log-view .list-cell {
    -fx-background-color: null; // removes alternating list gray cells.

.log-view .list-cell:debug {
    -fx-text-fill: gray;

.log-view .list-cell:info {
    -fx-text-fill: green;

.log-view .list-cell:warn {
    -fx-text-fill: purple;

.log-view .list-cell:error {
    -fx-text-fill: red;

import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.collections.transformation.FilteredList;
import javafx.css.PseudoClass;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Priority;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.util.Duration;

import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.LinkedBlockingDeque;

class Log {
    private static final int MAX_LOG_ENTRIES = 1_000_000;

    private final BlockingDeque<LogRecord> log = new LinkedBlockingDeque<>(MAX_LOG_ENTRIES);

    public void drainTo(Collection<? super LogRecord> collection) {

    public void offer(LogRecord record) {

class Logger {
    private final Log log;
    private final String context;

    public Logger(Log log, String context) {
        this.log = log;
        this.context = context;

    public void log(LogRecord record) {

    public void debug(String msg) {
        log(new LogRecord(Level.DEBUG, context, msg));

    public void info(String msg) {
        log(new LogRecord(Level.INFO, context, msg));

    public void warn(String msg) {
        log(new LogRecord(Level.WARN, context, msg));

    public void error(String msg) {
        log(new LogRecord(Level.ERROR, context, msg));

    public Log getLog() {
        return log;

enum Level { DEBUG, INFO, WARN, ERROR }

class LogRecord {
    private Date   timestamp;
    private Level  level;
    private String context;
    private String message;

    public LogRecord(Level level, String context, String message) {
        this.timestamp = new Date();
        this.level     = level;
        this.context   = context;
        this.message   = message;

    public Date getTimestamp() {
        return timestamp;

    public Level getLevel() {
        return level;

    public String getContext() {
        return context;

    public String getMessage() {
        return message;

class LogView extends ListView<LogRecord> {
    private static final int MAX_ENTRIES = 10_000;

    private final static PseudoClass debug = PseudoClass.getPseudoClass("debug");
    private final static PseudoClass info  = PseudoClass.getPseudoClass("info");
    private final static PseudoClass warn  = PseudoClass.getPseudoClass("warn");
    private final static PseudoClass error = PseudoClass.getPseudoClass("error");

    private final static SimpleDateFormat timestampFormatter = new SimpleDateFormat("HH:mm:ss.SSS");

    private final BooleanProperty       showTimestamp = new SimpleBooleanProperty(false);
    private final ObjectProperty<Level> filterLevel   = new SimpleObjectProperty<>(null);
    private final BooleanProperty       tail          = new SimpleBooleanProperty(false);
    private final BooleanProperty       paused        = new SimpleBooleanProperty(false);
    private final DoubleProperty        refreshRate   = new SimpleDoubleProperty(60);

    private final ObservableList<LogRecord> logItems = FXCollections.observableArrayList();

    public BooleanProperty showTimeStampProperty() {
        return showTimestamp;

    public ObjectProperty<Level> filterLevelProperty() {
        return filterLevel;

    public BooleanProperty tailProperty() {
        return tail;

    public BooleanProperty pausedProperty() {
        return paused;

    public DoubleProperty refreshRateProperty() {
        return refreshRate;

    public LogView(Logger logger) {

        Timeline logTransfer = new Timeline(
                new KeyFrame(
                        event -> {

                            if (logItems.size() > MAX_ENTRIES) {
                                logItems.remove(0, logItems.size() - MAX_ENTRIES);

                            if (tail.get()) {

        this.pausedProperty().addListener((observable, oldValue, newValue) -> {
            if (newValue && logTransfer.getStatus() == Animation.Status.RUNNING) {

            if (!newValue && logTransfer.getStatus() == Animation.Status.PAUSED && getParent() != null) {

        this.parentProperty().addListener((observable, oldValue, newValue) -> {
            if (newValue == null) {
            } else {
                if (!paused.get()) {

        filterLevel.addListener((observable, oldValue, newValue) -> {
                    new FilteredList<LogRecord>(
                            logRecord ->
                                logRecord.getLevel().ordinal() >=

        setCellFactory(param -> new ListCell<LogRecord>() {
                showTimestamp.addListener(observable -> updateItem(this.getItem(), this.isEmpty()));

            protected void updateItem(LogRecord item, boolean empty) {
                super.updateItem(item, empty);

                pseudoClassStateChanged(debug, false);
                pseudoClassStateChanged(info, false);
                pseudoClassStateChanged(warn, false);
                pseudoClassStateChanged(error, false);

                if (item == null || empty) {

                String context =
                        (item.getContext() == null)
                                ? ""
                                : item.getContext() + " ";

                if (showTimestamp.get()) {
                    String timestamp =
                            (item.getTimestamp() == null)
                                    ? ""
                                    : timestampFormatter.format(item.getTimestamp()) + " ";
                    setText(timestamp + context + item.getMessage());
                } else {
                    setText(context + item.getMessage());

                switch (item.getLevel()) {
                    case DEBUG:
                        pseudoClassStateChanged(debug, true);

                    case INFO:
                        pseudoClassStateChanged(info, true);

                    case WARN:
                        pseudoClassStateChanged(warn, true);

                    case ERROR:
                        pseudoClassStateChanged(error, true);

class Lorem {
    private static final String[] IPSUM = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque hendrerit imperdiet mi quis convallis. Pellentesque fringilla imperdiet libero, quis hendrerit lacus mollis et. Maecenas porttitor id urna id mollis. Suspendisse potenti. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Cras lacus tellus, semper hendrerit arcu quis, auctor suscipit ipsum. Vestibulum venenatis ante et nulla commodo, ac ultricies purus fringilla. Aliquam lectus urna, commodo eu quam a, dapibus bibendum nisl. Aliquam blandit a nibh tincidunt aliquam. In tellus lorem, rhoncus eu magna id, ullamcorper dictum tellus. Curabitur luctus, justo a sodales gravida, purus sem iaculis est, eu ornare turpis urna vitae dolor. Nulla facilisi. Proin mattis dignissim diam, id pellentesque sem bibendum sed. Donec venenatis dolor neque, ut luctus odio elementum eget. Nunc sed orci ligula. Aliquam erat volutpat.".split(" ");
    private static final int MSG_WORDS = 8;
    private int idx = 0;

    private Random random = new Random(42);

    synchronized public String nextString() {
        int end = Math.min(idx + MSG_WORDS, IPSUM.length);

        StringBuilder result = new StringBuilder();
        for (int i = idx; i < end; i++) {
            result.append(IPSUM[i]).append(" ");

        idx += MSG_WORDS;
        idx = idx % IPSUM.length;

        return result.toString();

    synchronized public Level nextLevel() {
        double v = random.nextDouble();

        if (v < 0.8) {
            return Level.DEBUG;

        if (v < 0.95) {
            return Level.INFO;

        if (v < 0.985) {
            return Level.WARN;

        return Level.ERROR;


public class LogViewer extends Application {
    private final Random random = new Random(42);

    public void start(Stage stage) throws Exception {
        Lorem  lorem  = new Lorem();
        Log    log    = new Log();
        Logger logger = new Logger(log, "main");"Hello");
        logger.warn("Don't pick up alien hitchhickers");

        for (int x = 0; x < 20; x++) {
            Thread generatorThread = new Thread(
                    () -> {
                        for (;;) {
                                    new LogRecord(

                            try {
                            } catch (InterruptedException e) {
                    "log-gen-" + x

        LogView logView = new LogView(logger);

        ChoiceBox<Level> filterLevel = new ChoiceBox<>(

        ToggleButton showTimestamp = new ToggleButton("Show Timestamp");

        ToggleButton tail = new ToggleButton("Tail");

        ToggleButton pause = new ToggleButton("Pause");

        Slider rate = new Slider(0.1, 60, 60);
        Label rateLabel = new Label();
        rateLabel.textProperty().bind(Bindings.format("Update: %.2f fps", rate.valueProperty()));
        rateLabel.setStyle("-fx-font-family: monospace;");
        VBox rateLayout = new VBox(rate, rateLabel);

        HBox controls = new HBox(

        VBox layout = new VBox(
        VBox.setVgrow(logView, Priority.ALWAYS);

        Scene scene = new Scene(layout);

    public static void main(String[] args) {

The section below on selectable text is supplemental to the solution posted above. If you don't need selectable text, you can ignore the selection below.

Is it possible to make the text selectable?

There a few different options:

  1. It is a ListView, so you could use a multipe selection model, ensuring the CSS is configured to appropriately style the selected rows as you wish. That will do a row by row selection, not a straight text selection. You can add a listener to the selected items in the selection model and do appropriate processing when that changes.
  2. You could use a factory for the ListView which sets each cell to an appropriately styles read-only text field. That would allow somebody to select just a portion of text within a row rather than a whole row. But they wouldn't be able to select text across multiple rows in one go.
  3. Rather than a ListView, you could base the implementation on a third-party read-only RichTextFX control, which would allow selection of text across multiple rows.

Try implementing the text selection approach which is appropriate for you and, if you can't get it to work, create a new question specific to selectable text logs, with a mcve.

6/8/2018 6:13:12 PM

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