JavaFx-sqlite登录屏幕如何解决登录代码中的异常

这部分的代码有问题。我得到了一个成功的构建，但当我按下我的登录按钮时，我没有看到主屏幕。堆栈跟踪中出现的错误如下：

ant -f /home/tacomeat/NetBeansProjects/BlackJackFx jfxsa-run
init:
Deleting: /home/tacomeat/NetBeansProjects/BlackJackFx/build/built-jar.properties
deps-jar:
Updating property file:/home/tacomeat/NetBeansProjects/BlackJackFx/build/built-jar.properties
Copying 1 file to /home/tacomeat/NetBeansProjects/BlackJackFx/build/classes
 compile:
 Deleting directory/home/tacomeat/NetBeansProjects/BlackJackFx/dist/lib
 Copying 1 file to /home/tacomeat/NetBeansProjects/BlackJackFx/dist/lib
 Detected JavaFX Ant API version 1.3
 Launching <fx:jar> task from /usr/lib/jvm/java-8-oracle/jre/../lib/ant-javafx.jar
 Warning: From JDK7u25 the Codebase manifest attribute should be used   to restrict JAR repurposing.
     Please set manifest.custom.codebase property to override the  current default non-secure value '*'.
    Launching <fx:deploy> task from /usr/lib/jvm/java-8-  oracle/jre/../lib/ant-javafx.jar
   No base JDK. Package will use system JRE.
  No base JDK. Package will use system JRE.
  jfx-deployment-script:
  jfx-deployment:
  jar:
Copying 13 files to   /home/tacomeat/NetBeansProjects/BlackJackFx/dist/run831901790
jfx-project-run:
Executing /home/tacomeat/NetBeansProjects/BlackJackFx/dist/run831901790/BlackJackFx. jar using platform /usr/lib/jvm/java-8-oracle/jre/bin/java
Login Now
Exception in thread "JavaFX Application Thread"java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.lambda$null$49(GtkApplication.java:139)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at  sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 48 more
Caused by: java.lang.NullPointerException
at com.blackjack.view.LoginController.isValidCredentials(LoginController.java:76)
at com.blackjack.view.LoginController.handleButtonAction(LoginController.java:58)
... 58 more
Deleting directory  /home/tacomeat/NetBeansProjects/BlackJackFx/dist/run831901790
 jfxsa-run:
 BUILD SUCCESSFUL (total time: 10 seconds)

---

我的错误在哪里？因为我看不到它？

@James\u D第76行是私有布尔IsValidCreditionals方法-我尝试改变一些情况，但仍然得到异常错误…该方法中的哪一行？私有布尔IsValidCreditional我得到了这两个原因：由java.lang.reflect.InvocationTargetException引起，以及这两个原因行：由以下原因引起：com.blackjack.view.LoginController.isValidCredentialsLoginController.java:79位于com.blackjack.view.LoginController.handleButtonActionLoginController.java:61这是第78和79行：布尔let_in=false；System.out.println从USERNAME=+'+USERNAME_-box.getText+'+和PASSWORD=+'+PASSWORD_-box.getText+'的用户中选择*；这就是第61行发生的情况：如果isValidCredentials{app_stage.hide；app_stage.setScenehome_page_scene；app_stage.show；}@James_D第76行是私有布尔IsValidCreditionals方法-我尝试改变情况，但仍然得到异常错误…该方法中的哪一行？私有布尔IsValidCreditional我得到以下两个原因：由java.lang.reflect.InvocationTargetException引起，这两行：由java.lang.NullPointerException引起在com.blackjack.view.LoginController.isValidCredentialsLoginController.java:79在com.blackjack.view.LoginController.handleButtonActionLoginController.java:61这是第78&79行：布尔let_in=false；System.out.println从USERNAME=+'+USERNAME_-box.getText+'+和PASSWORD=+'+PASSWORD_-box.getText+'的用户中选择*；这就是第61行发生的情况：如果isValidCredentials{app_stage.hide；app_stage.setScenehome_page_scene；app_stage.show；}

public class LoginController implements Initializable {


@FXML
private Label welcome;

@FXML
private Label warningLbl;

@FXML
private TextField username_box;

@FXML
private TextField password_box;


@FXML
private void handleButtonAction(ActionEvent event) throws IOException {


    System.out.println("Login Now");
    Parent home_page_parent = FXMLLoader.load(getClass().getResource("table.fxml"));
    Scene home_page_scene = new Scene(home_page_parent);
    Stage app_stage = (Stage) ((Node) event.getSource()).getScene().getWindow();

    if (isValidCredentials())
        {
           app_stage.hide();
           app_stage.setScene(home_page_scene);
           app_stage.show();
        }
    else
        {
          username_box.clear();
          password_box.clear();
          warningLbl.setText("Invalid Username or Password! ");
        }

}

private boolean isValidCredentials()
{
    boolean let_in = false;System.out.println("SELECT * FROM Users WHERE USERNAME= " + "'" + username_box.getText() + "'"
        + "AND PASSWORD=" + "'" + password_box.getText() + "'");

    Connection c = null;
    java.sql.Statement stmt = null;
    try{
        c = DriverManager.getConnection("jdbc:sqlite:BjFx.db");
        c.setAutoCommit(false);

        System.out.println("Opened database successfully");
        stmt = c.createStatement();

         ResultSet rs = stmt.executeQuery( "SELECT * FROM Users WHERE USERNAME= " + "'" + username_box.getText() + "'" 
        + " AND PASSWORD= " + "'" + password_box.getText() + "'");

        while ( rs.next() ) {
             if (rs.getString("USERNAME") != null && rs.getString("PASSWORD") != null) { 
                 String  username = rs.getString("USERNAME");
                 System.out.println( "USERNAME = " + username );
                 String password = rs.getString("PASSWORD");
                 System.out.println("PASSWORD = " + password);
                 let_in = true;
            }
        }
        rs.close();
        stmt.close();
        c.close();
        } catch ( Exception e ) {
            System.err.println( e.getClass().getName() + ": " + e.getMessage() );
            System.exit(0);
        }
        System.out.println("Operation done successfully");
        return let_in;

}      

@Override
public void initialize(URL url, ResourceBundle rb) {
    // TODO
}

}