JavaFX 和 maven:NullPointerException:需要位置 [英] JavaFX and maven: NullPointerException: Location is required

问题描述

我一直在尝试使用 JavaFX 设置 Maven.尽管我对 Maven 和 JavaFX 没有经验，但我没想到它会是一个如此大的挑战.我的 Java 知识非常扎实(包括 Swing)，没想到设置起来会这么困难.

I have been trying to get Maven set up with JavaFX. Even though I was unexperienced with Maven and JavaFX, I didn't expect it to be so much of a challenge. My Java knowledge is pretty solid (including Swing), and didn't expect to have this much difficulty getting it set up.

我从 IntelliJ 13.0 Community Edition 提供的 JavaFX 项目开始.我的Main类中的代码比较少:

I started with a JavaFX project supplied by IntelliJ 13.0 Community Edition. The code in my Main class is relatively small:

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application
{
    @Override
    public void start(Stage primaryStage) throws Exception
    {
        //getClass().getResource("../../resources/sample.fxml");
        Parent root = FXMLLoader.load(getClass().getResource("../sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root, 300, 275));
        primaryStage.show();
    }


    public static void main(String[] args)
    {
        launch(args);
    }
}

而且我的 pom.xml 也不是太大:

and my pom.xml isn't too big either:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>sample</groupId>
    <artifactId>JavaFXDemo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <organization>
        <name>RubberDucky</name>
    </organization>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>com.zenjava</groupId>
                    <artifactId>javafx-maven-plugin</artifactId>
                    <version>2.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
        <plugins>
            <plugin>
                <groupId>com.zenjava</groupId>
                <artifactId>javafx-maven-plugin</artifactId>
                <version>2.0</version>
                <configuration>
                    <mainClass>sample.Main</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>javafx</artifactId>
            <version>2.2</version>
            <systemPath>${java.home}/lib/jfxrt.jar</systemPath>
            <scope>system</scope>
        </dependency>
    </dependencies>
</project>

我正在使用 JavaFX Maven 插件 来构建应用程序.运行 mvn clean jfx:jar 后一切正常，所有构建成功.但是当我尝试运行该应用程序时，出现以下错误:

I'm using the JavaFX Maven Plugin to build the application. After running mvn clean jfx:jar everything seems fine, all builds succeed. But when I try to run the application I get the following error:

Exception in Application start method
java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at com.javafx.main.Main.launchApp(Main.java:698)
        at com.javafx.main.Main.main(Main.java:871)
Caused by: java.lang.RuntimeException: Exception in Application start method
        at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown So
urce)
        at com.sun.javafx.application.LauncherImpl.access$000(Unknown Source)
        at com.sun.javafx.application.LauncherImpl$1.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException: Location is required.
        at javafx.fxml.FXMLLoader.load(Unknown Source)
        at javafx.fxml.FXMLLoader.load(Unknown Source)
        at javafx.fxml.FXMLLoader.load(Unknown Source)
        at javafx.fxml.FXMLLoader.load(Unknown Source)
        at javafx.fxml.FXMLLoader.load(Unknown Source)
        at sample.Main.start(Main.java:15)
        at com.sun.javafx.application.LauncherImpl$5.run(Unknown Source)
        at com.sun.javafx.application.PlatformImpl$5.run(Unknown Source)
        at com.sun.javafx.application.PlatformImpl$4$1.run(Unknown Source)
        at com.sun.javafx.application.PlatformImpl$4$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.application.PlatformImpl$4.run(Unknown Source)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.access$100(Unknown Source)
        at com.sun.glass.ui.win.WinApplication$3$1.run(Unknown Source)
        ... 1 more

经过一些粗略的调试后，问题似乎出在我加载文件的路径上.将 sample.fxml 硬编码到我硬盘上的某个位置后，应用程序运行没有任何问题.从 IntelliJ 运行应用程序时，当前设置(如上所示)也是如此.

After some rough debugging the trouble seems to be in the path I am loading my files from. After hardcoding the sample.fxml to a place on my hard drive, the application runs without any problems. Same goes for the current setup (seen above) when running the application from IntelliJ.

我觉得我已经用尽了所有资源(包括 StackOverflow，一些非常相似的错误)，但我就是无法弄清楚到底是哪里出了问题.

I feel like I have exhausted every resource (including StackOverflow, some very similar errors) but I just can't figure out what exactly is wrong.

推荐答案

确保您的 sample.fxml 位于 src/main/resources/ 目录(或子目录).然后你可以像这样访问文件:

Make sure that your sample.fxml is in the src/main/resources/ directory (or a subdirectory). Then you can access the file like this:

Parent root = FXMLLoader.load(getClass().getClassLoader().getResource("sample.fxml"));

说明:在编译阶段，所有资源和类都被复制到 target/classes/.因此，您的 fxml 文件位于此目录中，而您的类位于关于其包名称的子目录中.如果您调用 getClass().getResource("sample.fxml"); 该文件将相对于该目录的类文件进行搜索:target/classes/sample/代码>.

Explanation: During the compile phase all resources and classes get copied to target/classes/. So your fxml file resides in this directory and your class in a subdirectory regarding its package name. If you call getClass().getResource("sample.fxml"); the file will be searched relative to the class file which will be this directory: target/classes/sample/.

在类加载器上调用 .getResource() 将相对搜索路径设置为 target/classes/，从而找到您的文件.

Calling .getResource() on the classloader sets the relative search path to target/classes/ and therefore your file gets found.

附言你也可以写:

Parent root = FXMLLoader.load(getClass().getResource("/sample.fxml"));

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