java.lang.IllegalStateException:Not on FX application when using quartz

Question

I'm trying to use a javafx alert in a task schedule in quartz:

public class ChecarJob implements Job{
    private Connection con;
    public ChecarJob() {
        this.con = new ConnectionFactory().getConnection();
    }
    public void execute(JobExecutionContext context) throws JobExecutionException {
        System.out.println("Executou!");
                try {
                    String verStatus = "SELECT COUNT(*) FROM equipamento_requisicao";
                    PreparedStatement stmt = con.prepareStatement(verStatus);
                        ResultSet rsStatus = stmt.executeQuery();
                        if(rsStatus.next()){
                        Alerts a = new Alerts();
                        int Resultado = rsStatus.getInt(1);
                        if(Resultado>Sessao.getInstancia().getQtdRegistroBD()){
                        Sessao.getInstancia().setQtdRegistroBD(Resultado);
                                                Alert alert = new Alert(Alert.AlertType.INFORMATION);
                        alert.setTitle("SUCESS");
                        alert.setHeaderText("SUCESS");
                        alert.setContentText("SUCESS");
                        alert.showAndWait();
                        }
                        else if(Resultado<Sessao.getInstancia().getQtdRegistroBD()){
                        Alert alert = new Alert(Alert.AlertType.INFORMATION);
                        alert.setTitle("FAIL");
                        alert.setHeaderText("FAIL");
                        alert.setContentText("FAIL");
                        alert.showAndWait();
                        Sessao.getInstancia().setQtdRegistroBD(Resultado);
                        } 
                        else{
                        //aq não irei fazer nada.
                        }
                        }
                    }catch (Exception e) {
            e.printStackTrace();
                    }
    }   

}

calling in my main class:

public void start(Stage stage) throws Exception {
    JobDetail j = JobBuilder.newJob(ChecarJob.class).build();
    Trigger t = TriggerBuilder.newTrigger().withIdentity("CroneTrigger")
            .withSchedule(SimpleScheduleBuilder.simpleSchedule().withIntervalInSeconds(60).repeatForever()).build();
    Scheduler s = StdSchedulerFactory.getDefaultScheduler();
    s.start();
    s.scheduleJob(j,t);

msg do error:

java.lang.IllegalStateException: Not on FX application thread; currentThread = DefaultQuartzScheduler_Worker-2Executou!

Answer 1

JavaFX, like most UI toolkits, is single-threaded and not thread-safe. Once a scene graph is being displayed in a window, it must only be interacted with on the JavaFX Application Thread. And some objects must be instantiated on the FX thread. To do otherwise can lead to errors, as you've encountered, or just full on undefined behavior. If you're on a background thread and you need to schedule an action with the FX thread, you can use Platform.runLater(Runnable) (link is to the Javadoc).

Your code is not a minimal and complete example, so I can't be sure of what everything does. In general, however, I would start by moving all the code relating to Alert instances into a runLater call.

public void execute(JobExecutionContext context) throws JobExecutionException {
    System.out.println("Executou!");
    try {
        String verStatus = "SELECT COUNT(*) FROM equipamento_requisicao";
        PreparedStatement stmt = con.prepareStatement(verStatus);
        ResultSet rsStatus = stmt.executeQuery();
        if (rsStatus.next()) {
            Alerts a = new Alerts(); // what does this do?
            int Resultado = rsStatus.getInt(1);
            if (Resultado > Sessao.getInstancia().getQtdRegistroBD()) {
                Sessao.getInstancia().setQtdRegistroBD(Resultado); // unknown side-effects
                Platform.runLater(() -> {
                    Alert alert = new Alert(Alert.AlertType.INFORMATION);
                    alert.setTitle("SUCESS");
                    alert.setHeaderText("SUCESS");
                    alert.setContentText("SUCESS");
                    alert.showAndWait();
                });
            } else if (Resultado < Sessao.getInstancia().getQtdRegistroBD()) {
                Platform.runLater(() -> {
                    Alert alert = new Alert(Alert.AlertType.INFORMATION);
                    alert.setTitle("FAIL");
                    alert.setHeaderText("FAIL");
                    alert.setContentText("FAIL");
                    alert.showAndWait();
                });
                Sessao.getInstancia().setQtdRegistroBD(Resultado); // unknown side-effects
            } else {
                //aq não irei fazer nada.
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Some notes:

• The above uses lambda expressions.
• Don't forget to close resources (e.g. PreparedStatement, ResultSet) when done with them. Use try-with-resources.
• The calls to runLater do not wait for the Runnable to return.
• The "unknown side-effects" comments are there because I have no idea if those method invocations modify the UI. I've left them out of the runLater call on the assumption that they don't.
• I couldn't find where Alerts a = new Alerts() is actually used.
• The name Resultado does not follow standard Java naming conventions for local variables.
• Notice that properly indenting your code makes it much easier to read and follow what is happening.

---

I am new to java and do not understand much about threads

Not having at least a basic understanding of concurrency in Java will hinder your efforts to create all but the most trivial of GUI applications. I highly recommend you study this topic before moving forward. As a start, read these:

• Lesson: Concurrency
• Concurrency in JavaFX

Also, a good book on the topic is Java Concurrency in Practice by Brian Goetz et al.