我有一个应用程序在登录时通过接口类访问数据库。登录过程导致应用程序在访问数据库时没有响应一段时间，因此我一直在查看线程和等待光标以使其顺利运行。我试图通过Web上的许多示例和堆栈溢出来使用线程，但我的方法似乎没有工作，我收到java.lang.IllegalStateException：不在FX应用程序线程上; currentThread = Thread-4异常，我不知道如何从这里开始。我试图做的是将光标更改为WAIT模式，而后台线程正在运行loginLoadEverything（）方法（虽然我没有在其中包含代码，因为它太长）。这是我的控制器类：
package main.java.gui;
import javafx.application.Platform;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Cursor;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.stage.Stage;
import main.java.databaseInterface.BackendInterface;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.concurrent.CountDownLatch;
public class LoginController implements Initializable {
private BackendInterface backendInterface;
private DashboardController dashboardController;
private StudentsController studentsController;
private ConsultationController consultationController;
private CreateStudentController createStudentController;
private CreateConsultationController createConsultationController;
@FXML
TextField username;
@FXML
PasswordField password;
@FXML
Button loginButton;
@FXML
Label loginLabel;
@FXML
public void loginButtonPress(ActionEvent event) {
Service<Void> service = new Service<Void>() {
@Override
protected Task<Void> createTask() {
return new Task<Void>() {
@Override
protected Void call() throws Exception {
loginLoadEverything();
final CountDownLatch latch = new CountDownLatch(1);
Platform.runLater(new Runnable() {
@Override
public void run() {
try {
Scene s1 = loginLabel.getScene();
s1.setCursor(Cursor.WAIT);
} finally {
latch.countDown();
}
}
});
latch.await();
return null;
}
};
}
};
service.start();
}
public void loginLoadEverything() {
//chance to true when complete
if (username.getText().isEmpty() == false || password.getText().isEmpty() == false) {
loginLabel.setText("Please enter data in the fields below");
} else {
username.setText("-----");
password.setText("-----");
//initialises backend interface with username and password
backendInterface = new BackendInterface(username.getText(), password.getText().toCharArray());
// Open a connection to the database
if (backendInterface.openConnection()) {
//return and print response
System.out.println(backendInterface.getConnectionResponse());
//directs the user to the dashboard after successful login
try {
if (backendInterface.getAllStudents() &&
backendInterface.getAllConsultations() &&
backendInterface.getCourses() &&
backendInterface.getConsultationCategories() &&
backendInterface.getConsultationPriorities()) {
FXMLLoader loader1 = new FXMLLoader();
loader1.setLocation(getClass().getResource("/main/res/dashboard.fxml"));
loader1.load();
Parent p = loader1.getRoot();
Stage stage = new Stage();
stage.setScene(new Scene(p));
stage.show();
//set instances to the dashboard controller
dashboardController = loader1.getController();
dashboardController.setBackendInterface(backendInterface); //pass backendInterface object to controller
dashboardController.setDashboardController(loader1.getController()); //pass dashboard as reference
//load images
Image logoutImage = new Image(getClass().getResourceAsStream("images/logout.png"));
Image userImage = new Image(getClass().getResourceAsStream("images/users.png"));
Image calendarImage = new Image(getClass().getResourceAsStream("images/calendar.png"));
Image leftArrowImage = new Image(getClass().getResourceAsStream("images/leftArrow.png"));
Image notepadImage = new Image(getClass().getResourceAsStream("images/notepad.png"));
//set images
dashboardController.studentLabel.setGraphic(new ImageView(userImage));
dashboardController.logoutLabel.setGraphic(new ImageView(logoutImage));
dashboardController.consultationLabel.setGraphic(new ImageView(notepadImage));
} else {
system.out.println(backendInterface.getExceptionMessage);
}
@Override
public void initialize(URL location, ResourceBundle resources) {
}
答案 0 :(得分：3)
您可能在这里不需要Service：您只需要一个Task。
call()方法是在后台线程上执行的方法。它应该执行需要很长时间才能执行的工作（即连接到数据库并从中获取数据）并且不得执行任何UI工作，因为对UI 的更改必须在FX应用程序主题上进行。您获得异常的原因是您正在从后台线程创建并显示Stage。
所以基本的想法是让任务从数据库中获取数据并返回它;然后使用onSucceeded处理程序为任务显示UI，使用任务的结果。 （onSucceeded处理程序在FX应用程序线程上执行，允许您在此处安全地修改UI。）
我不确切地知道你的课程是如何实现的，但是以下几行可能会有效。重要的是，你不能在与UI交互的后台线程中做任何事情。
@FXML
public void loginButtonPress(ActionEvent event) {
if (( ! username.getText().isEmpty()) || (! password.getText().isEmpty()) ) {
loginLabel.setText("Please enter data in the fields below");
} else {
// I assume you want these values before you set them to "-----", no???
final String uName = username.getText();
final char[] pw = password.getText().toCharArray();
username.setText("-----");
password.setText("-----");
// create task for retrieving data:
Task<BackendInterface> loadDataTask = new Task<BackendInterface>() {
@Override
public BackendInterface call() throws Exception {
BackendInterface backendInterface = new BackendInterface(uName, pw);
if (backendInterface.openConnection()) {
if (backendInterface.getAllStudents() &&
backendInterface.getAllConsultations() &&
backendInterface.getCourses() &&
backendInterface.getConsultationCategories() &&
backendInterface.getConsultationPriorities()) {
return backendInterface ;
}
}
// maybe throw an exception here, depending on your requirements...
return null ;
}
};
// show UI on task completion:
loadDataTask.setOnSucceeded(e -> {
BackendInterface backendInterface = loadDataTask.getValue();
if (backendInterface == null) {
// something went wrong... bail, or probably show error message...
return ;
}
FXMLLoader loader1 = new FXMLLoader();
loader1.setLocation(getClass().getResource("/main/res/dashboard.fxml"));
Parent p = loader1.load();
DashboardController controller = loader.getController();
controller.setBackendInterface(backendInterface);
Stage stage = new Stage();
stage.setScene(new Scene(p));
stage.show();
// etc etc with your Images, etc (not sure why this isn't done in DashboardController though...)
// set cursor back to default:
loginLabel.getScene().setCursor(Cursor.DEFAULT);
});
loadDataTask.setOnFailed(e -> {
// show error message or otherwise handle database exception here
});
// set cursor to WAIT:
loginLabel.getScene().setCursor(Cursor.WAIT);
// and run task in a background thread:
Thread t = new Thread(loadDataTask);
t.start();
}