I am trying to make my JavaFx-Application executable using Maven and Visual Studio Code.
After some time spent on this topic, I found some posts mentioning jlink.
I am a newcomer when it comes to packaging Java/JavaFX applications, so I gave it a try.
Currently, I can at least execute the launcher for the package.
But immediately after starting the application, a NullPointerException is thrown: Cannot invoke "Object.toString()" because the return value of "java.lang.Class.getResource(String)" is null.
For styling the components of my view I created some .css-files and put them inside a /style directory. This directory I placed this, according to the sample JavaFx application, inside a /resources directory created by Maven. In a similar manner, I proceeded with my sound and image files.
Here you can see an excerpt of my directory structure.
|
|--src/main
| |
| |-- java
| | | ...
| |
| |-- resources
| |
| |-- img
| | | ...
| |
| |-- style
| | | ...
| |
| |-- sound
| | ...
|
|-- target
|
|-- classes
| | ...
| |
| |-- img
| | | ...
| |
| |-- style
| | | ...
| |
| |-- sound
| | | ...
|
|-- ...
|
|-- app
|
|-- bin
|-- ...
Now I am trying to access my resources from within my application.
This was my first approach. It works just fine when running from VSCode.
public static final String PATH_TO_STYLESHEET = App.class.getResource("/style").toString();
public static final String PATH_TO_IMG = App.class.getResource("/img").toString();
public static final String PATH_TO_SOUNDS = App.class.getResource("/sounds").toString();
But after running jlink, my application crashes, showing the NullPointerException mentioned earlier.
Here is my pom.xml:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.openjfx</groupId>
<artifactId>App</artifactId>
<version>0.0.1-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.release>19</maven.compiler.release>
<javafx.version>19</javafx.version>
<javafx.maven.plugin.version>0.0.8</javafx.maven.plugin.version>
</properties>
<dependencies>
<dependency>
<groupId>org.openjfx</groupId>
<artifactId>javafx-controls</artifactId>
<version>${javafx.version}</version>
</dependency>
<dependency>
<groupId>org.openjfx</groupId>
<artifactId>javafx-media</artifactId>
<version>${javafx.version}</version>
</dependency>
<dependency>
<groupId>org.openjfx</groupId>
<artifactId>javafx-fxml</artifactId>
<version>${javafx.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<release>${maven.compiler.release}</release>
</configuration>
</plugin>
<plugin>
<groupId>org.openjfx</groupId>
<artifactId>javafx-maven-plugin</artifactId>
<version>${javafx.maven.plugin.version}</version>
<configuration>
<release>${maven.compiler.release}</release>
<jlinkImageName>App</jlinkImageName>
<launcher>launcher</launcher>
<mainClass>com.test.App</mainClass>
</configuration>
</plugin>
</plugins>
<resources>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
</build>
</project>
And this is the command I have been using for creating the package.
mvn javafx:jlink -f pom.xml
Does anyone have an idea how I can get the path to my stylesheets, images, and sounds, after running jlink? The path is absolutely sufficient. I do not need a file itself.
Is there an option to copy the resources to a specific location?
CodePudding user response:
Problem
You have code such as the following:
public static final String PATH_TO_IMG = App.class.getResource("/img").toString();
This is trying to get the resource "/img"
. But according to your question, that is not a resource per se, but instead a directory (i.e., a package). And the problem appears to be the inconsistent behavior of Class#getResource(String)
when the String
argument denotes a directory. When your code is not in a JRT image then the call to #getResource(String)
will return a URL
; when your code is packaged in a JRT image then the same call will return null
, despite the fact the directory exists.
I don't know if this behavior is a bug or simply undefined. One interesting thing is ModuleReader#find(String)
clearly is capable of finding directories:
Finds a resource, returning a URI to the resource in the module.
If the module reader can determine that the name locates a directory then the resulting URI will end with a slash (
'/'
).
That indicates, to me at least, that what you're trying to do should be possible. But even that method fails when the module is packaged in a JRT image (by returning an empty Optional
). Note that if you query the ModuleReader#list()
method it will include directories when the module is not in a JRT image, but those same directories are not included when the module is in a JRT image.
Example
I've put a minimal example demonstrating this problem at the end of this answer.
A Solution
I assume you're using these constants (e.g., PATH_TO_IMG
) to do stuff like the following:
Image image = new Image(PATH_TO_IMG "foo.png");
Which avoids having calls to SomeClass.class.getResource("...").toString()
everywhere. If this is your goal, then I can think of at least one solution. Change your constants to simply reference the resource root. For example:
public static final String IMG_ROOT = "/img";
Then create a utility method to resolve the resource:
public static String getImagePath(String name) {
var resource = IMG_ROOT "/" name;
var url = App.class.getResource(resource);
if (url == null) {
throw new RuntimeException("could not find resource: " resource);
}
return url.toString();
}
And then you can use that utility method like so:
Image image = new Image(getImagePath("foo.png"));
Possible Alternative
Another option might be to make use of the JRT FileSystem
implementation. Something like the following:
FileSystem jrtFs = FileSystems.getFileSystem(URI.create("jrt:/"));
Path path = jrtFs.getPath("modules", "<module-name>", "img");
// Note: Doesn't seem to include the trailing '/'
String pathToImg = path.toUri().toString();
Though you'll have to detect if your code is in a JRT image or not.
Minimal Example
Given this doesn't have to do with JavaFX specifically, I've created a minimal example to demonstrate this problem.
- Maven 3.8.6
- OpenJDK 19.0.1 2022-10-18
- Tested on Windows 11
Source Code
Project structure:
| pom.xml
|
\---src
\---main
---java
| | module-info.java
| |
| \---sample
| Main.java
|
\---resources
\---data
file.txt
pom.xml:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>sample</groupId>
<artifactId>app</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.release>19</maven.compiler.release>
</properties>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.10.1</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-resources-plugin</artifactId>
<version>3.3.0</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.3.0</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jlink-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<launcher>app=app/sample.Main</launcher>
</configuration>
</plugin>
</plugins>
</build>
</project>
module-info.java:
module app {}
Main.java:
package sample;
public class Main {
public static void main(String[] args) {
var modRef = Main.class.getModule()
.getLayer()
.configuration()
.findModule(Main.class.getModule().getName())
.orElseThrow()
.reference();
System.out.printf("Module Location = %s%n%n", modRef.location().orElseThrow());
var dataUrl = Main.class.getResource("/data");
var fileUrl = Main.class.getResource("/data/file.txt");
System.out.printf("Data URL = %s%nFile URL = %s%n%n", dataUrl, fileUrl);
}
}
Building
I ran these two commands to build the project:
mvn compile jar:jar
mvn jlink:jlink
For whatever reason, doing mvn compile jar:jar jlink:jlink
caused the jlink
task to fail.
Output
And here is the different output for the different packaging:
Exploded module:
...> java -p target\classes -m app/sample.Main
Module Location = file:///C:/Users/***/Desktop/jlink-tests/target/classes/
Data URL = file:/C:/Users/***/Desktop/jlink-tests/target/classes/data/
File URL = file:/C:/Users/***/Desktop/jlink-tests/target/classes/data/file.txt
Modular JAR:
...> java -p target\app-1.0-SNAPSHOT.jar -m app/sample.Main
Module Location = file:///C:/Users/***/Desktop/jlink-tests/target/app-1.0-SNAPSHOT.jar
Data URL = jar:file:///C:/Users/***/Desktop/jlink-tests/target/app-1.0-SNAPSHOT.jar!/data/
File URL = jar:file:///C:/Users/***/Desktop/jlink-tests/target/app-1.0-SNAPSHOT.jar!/data/file.txt
JRT Image:
...> .\target\maven-jlink\default\bin\app
Module Location = jrt:/app
Data URL = null
File URL = jrt:/app/data/file.txt
Results
As you can see, the call to getResource("/data/file.txt")
worked every time, but the call to getResource("/data")
did not work for the JRT-packaged version.