JavaFX和maven:NullPointerException:位置是必需的

Question

我一直试图让Maven与JavaFX建立起来.尽管我对Maven和JavaFX缺乏经验,但我并不认为这是一个很大的挑战.我的Java知识非常可靠(包括Swing),并且没想到设置它会有这么大的困难.

我开始使用IntelliJ 13.0 Community Edition提供的JavaFX项目.我的Main类中的代码相对较小:

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);
    }
}

我pom.xml也不是太大了:

<?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.运行后mvn clean jfx:jar一切似乎都很好,所有构建成功.但是当我尝试运行应用程序时,我收到以下错误:

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,问题似乎出现在我从中加载文件的路径中.sample.fxml将硬盘编码到硬盘驱动器上的某个位置后,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.

我觉得我已经耗尽了所有资源(包括StackOverflow,一些非常类似的错误),但我无法弄清楚到底出了什么问题.

Answer 1

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

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文件驻留在此目录中,而您的类位于与其包名称相关的子目录中.如果你调用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/.

调用.getResource()类加载器会设置相对搜索路径target/classes/,从而找到您的文件.

PS你也可以这样写:

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

Answer 2

正如@ Absurd-Mind已经解释过的那样,maven不会复制位于src目录下的任何资源文件(如fxml).

如果要保留fxml除java源文件之外的文件,可以使用maven资源插件来复制它们:

<build>
    ...
    <resources>
        <resource>
            <filtering>false</filtering>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.fxml</include>
            </includes>             
        </resource>
    </resources>
    ...
</build>

Answer 3

我和Intelij和Gradle有同样的问题.

修复步骤:

1.移动文件

sample.fxml

路径

\ SRC \主\资源\ FXML

2. 在此文件上设置路径:

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