java - 文件迭代不适用于资源文件夹？

Question

为什么我无法迭代此示例中的文件:

private List<String> bilder;
    private int bildNummer;


    public void initialize(URL location, ResourceBundle bundle) {
        // before maven: ladeBilder(new File("/img/settings"));
        ladeBilder(new File(String.valueOf((SettingsController.class.getResource("/img/settings")))));
        //imgView.setImage(uebergebeBilder());
    }

    private Image uebergebeBilder() {
        if(bildNummer <= 13){
            String bild = bilder.get(bildNummer);
            bildNummer++;
            return new Image("sample/img/settings/"+bild);
        } else{
            bildNummer = 0;
            String bild = bilder.get(bildNummer);
            bildNummer++;
            return new Image("sample/img/settings/"+bild);
        }
    }

    private void ladeBilder(final File pfad) {
        if(bilder == null) {
            bilder = new ArrayList<String>();
        } else {
            bilder.clear();
        }

        File[] files = pfad.listFiles((dir, name) -> {
            if(name.equals(".DS_Store")){
                return false;}
            else if(name.equals("thumbs.db")){
                return false;
            }else{
                return true;
            }
        });
        for(File f : files) {
            if(f.isDirectory()) {
                ladeBilder(f);
            } else {
                bilder.add(f.getName());
            }
        }
    }

在我添加 Maven 框架之前它就起作用了。 System.out.println(String.valueOf((SettingsController.class.getResource("/img/settings")))); 给了我以下路径: 文件:/Users/****/****/Proggen/Passwort-Manager19/target/classes/img/settings 图像已加载到该路径中。我插入了几个 System.out.println(int) 来确定在哪个位置一切正常，并且 for(File f : files) { 之后的 System.out.println 未执行。 (抱歉，如果是 JavaFX 项目，我仍在努力阅读这些错误代码)

顺便说一句...如果我想制作一个 jar，我仍然可以使用 SettingsController.class.getResource("/img/settings") 吗？

是的，我知道 return new Image("sample/img/settings/"+bild); 不是正确的路径，但这不是问题所在。

这是日志:

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.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    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.control.MenuItem.fire(MenuItem.java:462)
    at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
    at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$6(ContextMenuContent.java:1358)
    at com.sun.javafx.event.CompositeEventHandler$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.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$MouseEventNotification.run(GlassViewEventHandler.java:394)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:410)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 40 more
Caused by: javafx.fxml.LoadException: 
/Users/****/****/Proggen/Passwort-Manager19/target/classes/sample/SettingsView.fxml

    at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
    at sample.MainController.settings(MainController.java:222)
    ... 50 more
Caused by: java.lang.NullPointerException
    at sample.SettingsController.ladeBilder(SettingsController.java:65)
    at sample.SettingsController.initialize(SettingsController.java:30)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    ... 53 more

Answer 1

显然，你改变了:

ladeBilder(new File("/img/settings"));

到

ladeBilder(new File(String.valueOf(
                    (SettingsController.class.getResource("/img/settings")))));

它停止工作了。问题是 getResource 不返回文件名。它返回一个 URL 然后使用 String.valueOf(Object) 将 URL 转换为字符串，然后将该字符串视为文件名.

但它不是文件名。它是一个 url 字符串。它看起来像这样:

    jar:file:/path/to/jar!/img/settings

因此，当您在该 url 字符串上 new File(urlString) 时，您将获得一个引用不存在文件的 File 对象。最终你会得到一个 NPE(显然)。

如何解决这个问题？

您想要做的是迭代资源路径中给定树中的资源。简而言之，您无法使用文件 I/O 库(File、Path、Files 等)来执行此操作，因为资源命名空间不是文件系统命名空间。

您需要使用替代方法。有多种方法可以做到这一点；请参阅以下内容:

• How to walk through Java class resources?
• How to walk a directory tree on the classpath looking resource files?

<小时/>

It worked before I add the Maven framework.

这不是 Maven 的错。

更好的描述是，当您从开发环境中的文件系统访问资源时，它起作用了。它崩溃了，因为您将资源包含在 JAR 文件中并更改了代码以从那里访问它们。

无论您使用什么方法创建 JAR 文件，都会发生这种情况。