java.lang.IllegalStateException：使用石英时不在FX应用程序上

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 (eg 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.