从应用程序上下文</string>返回ObservableList <string>

Question

我目前正在使用嵌入在应用程序类中的静态数据库类，它工作得很好。但是，当我从函数返回ObservableList<String>并尝试将其设置为ListView时，它会抛出Caused by: java.lang.reflect.InvocationTargetException。我知道这是一个线程问题，在这种情况下我无法弄清楚如何将值从应用程序线程传递回UI线程。我是JavaFX的新手。

控制器类：

public class SampleController implements Initializable {

    @FXML
    public ListView<String> lvGroup;

    @FXML
    private void OpenDbClick(ActionEvent event){
        System.out.println("open db");
        ObservableList<String> ol;
        ol = WeddingGuestList.DatabaseConn.getGroups();
        lvGroup.setItems(ol);   <-error occurs here
    }
}

数据库方法：

public static ObservableList<String> getGroups(){
    ObservableList<String> groups = FXCollections.observableArrayList();

    try{
       Statement stmt = con.createStatement();
       stmt.setQueryTimeout(30);
       ResultSet rs = stmt.executeQuery("Select * from GuestGroup");
       while (rs.next()){
           groups.add(rs.getString("Name"));
       }

    }catch (SQLException e){
        e.printStackTrace();
    }catch (Exception e){
        e.printStackTrace();
    }
    return groups;
}

我不明白我应该如何将数据恢复到ListView。

修改

堆栈跟踪：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1440)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Node.fireEvent(Node.java:6863)
    at javafx.scene.control.Button.fire(Button.java:179)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3328)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3168)
    at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3123)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1563)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2265)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:250)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:173)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:292)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:528)
    at com.sun.glass.ui.View.notifyMouse(View.java:922)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication$3$1.run(GtkApplication.java:82)
    at java.lang.Thread.run(Thread.java:724)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:75)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:279)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1435)
    ... 51 more
Caused by: java.lang.NullPointerException
    at testguesslist.SampleController.OpenDbClick(SampleController.java:56)
    ... 61 more

Answer 1

我不认为这是造成上述异常的原因，但是：

理想情况下，您应该在单独的线程中进行数据库调用，因为它可能需要一些时间，并且您不希望阻止JavaFX线程。
这样做的方法是将代码放在javafx.concurrent.Task中的OpenDbClick方法中（检查http://docs.oracle.com/javafx/2/threads/jfxpub-threads.htm）。

`
公共类SampleController {

    public ListView<String> lvGroup;
    private ExecutorService threadPool;



    private void OpenDbClick(ActionEvent event) {
        Task<Void> task = new Task<Void>() {

            @Override
            protected Void call() throws Exception {
                System.out.println("open db");
                final ObservableList<String> ol = WeddingGuestList.DatabaseConn.getGroups();
                Platform.runLater(new Runnable() {

                    @Override
                    public void run() {
                        lvGroup.setItems(ol);
                    }
                }); 
                return null;
            }
        };
        getPool().execute(task); 
    }

    private ExecutorService getPool() {
        if (threadPool == null) {
            threadPool = Executors.newCachedThreadPool();
        }
        return threadPool;
    }
}

`

Plaftorm.runLater将强制在JavaFX线程上执行其代码，而不是在任务线程上执行。 这很重要，因为设置列表视图的项列表将导致场景图的更新，这应该在UI线程上完成。如果您不使用Platform.runLater代码，上述操作将导致异常。

Answer 2

堆栈跟踪在此处显示问题..在testguesslist.SampleController.OpenDbClick(SampleController.java:56)

看起来这里的一个对象为null。请检查一下。或者，请发送此方法的第55,56和57行代码进行审核。