Develop Reference

Unable to launch a JavaFX application which uses Apache POI

I have a JavaFX application that works as expected. I need to use Apache POI to read and write excel files. The following are the steps I have taken:
Added the required dependency
implementation 'org.apache.poi:poi-ooxml:5.2.3'
Added the module to module-info.java
requires org.apache.poi.ooxml;
Tried to use the library within a function:
#FXML
private void downloadTemplate() {
XSSFWorkbook workbook = new XSSFWorkbook();
}
All this is fine with no issues. However when I try to run the application, I get the following two errors (interchanging)
> Task :Start.main() FAILED
Error occurred during initialization of boot layer
java.lang.module.FindException: Module SparseBitSet not found, required by org.apache.poi.ooxml
and
> Task :Start.main() FAILED
Error occurred during initialization of boot layer
java.lang.module.FindException: Module commons.math3 not found, required by org.apache.poi.ooxml
I can however, clearly see both libraries under 'external libraries'
I am using IntelliJ Community Edition 2022.1.2 and running the project using Java 17.0.1. Any help would be highly appreciated.

SparseBitSet is an automatic module, it has no module-info of its own (probably commons-math3 is as well), and is without an Automatic-Module-Name entry in its manifest.
Gradle puts libraries without a module-info.class or an Automatic-Module-Name in their manifest on the class path, not the module path, so they won't be treated as modules, and the module finder won't find them.
You can:
hack the gradle build to allow the modules to be found. (I don't use Gradle so I have no specific advice on how to do that other than referring to the documentation).
Hack the library jar which you want to be treated as a module to include a module-info.class or an Automatic-Module-Name in its manifest.
Or, switch to maven, which automatically places automatic modules on the module path.
The easiest way to do this, IMO, is to create a new JavaFX project in Idea, then add the required dependencies as maven dependencies and add your code.
Or, as swpalmer suggests in the comments, request that library maintainers update their codebase to make their libraries modular.
And, when you run your app, make sure all jars are on the module path, not the class path.
Or, make your app non-modular by removing the module-info.java from it, then manually place the JavaFX modules on the module-path and add them with the --add-modules switch.
FAQ
Are you SURE that automatic modules are put on the class path by Gradle?
From the Gradle documentation section Building Modules for the Java Module System:
To tell the Java compiler that a Jar is a module, as opposed to a
traditional Java library, Gradle needs to place it on the so called
module path. It is an alternative to the classpath, which is the
traditional way to tell the compiler about compiled dependencies.
Gradle will automatically put a Jar of your dependencies on the module
path, instead of the classpath, if these three things are true:
java.modularity.inferModulePath is not turned off
We are actually building a module (as opposed to a traditional
library) which we expressed by adding the module-info.java file.
(Another option is to add the Automatic-Module-Name Jar manifest
attribute as described further down.)
The Jar our module depends on is itself a module, which Gradles
decides based on the presence of a module-info.class — the compiled
version of the module descriptor — in the Jar. (Or, alternatively, the
presence of an Automatic-Module-Name attribute the Jar manifest)
It is the third point that is key. Java can treat a library with no module-info.class and no Automatic-Module-Name in the Jar manifest as an automatic module if it is on the module path. However, Gradle will by default, only place libraries which fulfill one of those two conditions on the module path.

Using jewelsea's answer above, I have been able to solve the problem. I am posting the answer here to help anyone else who encounters the problem in future.
So, the overall problem is, as said in the answer above, both SparseBitSet and commons-math3 are automatic modules with no module-info of their own. The solution that worked for me was to convert them into the modules expected by the project. Here are the steps I took:
Use a gradle plugin 'extra-java-module-info'. The github page didn't show how to import it to a normal gradle file so here it is:
plugins {
id 'org.gradlex.extra-java-module-info' version '1.0'
}
Note the names that your application expects for the modules. In my case, from the error messages thrown, they were 'SparseBitSet' and 'commons-math3'
Locate the said libraries on the sidebar under 'external libraries' and note the 'jar' file names. In my case, they were 'commons-math3-3.6.1.jar' and 'SparseBitSet-1.2.jar'.
Add a section 'extraJavaModuleInfo' to your gradle files and use the parameters as follows: module('jar file name', 'name expected by your project', 'jar version'), as shown in the blue rectangle in the image above.
extraJavaModuleInfo {
module('commons-math3-3.6.1.jar', 'commons.math3', '3.6.1')
module('SparseBitSet-1.2.jar', 'SparseBitSet', '1.2')
}
That's it. Try to sync and run your project. Thanks jewelsea.

Java FX Modular Application, Module not found (Java 17, Intellij)

Hello I have a problem with my modular Java FX Application.
First of all I created a JavaFX Project with the Intellij Wizard.
I added the Java FX lib:enter image description here
I also added the VM options:enter image description here
But I always get this errormessage:enter image description here
"Error occurred during initialization of boot layer
java.lang.module.FindException: Module com.example.hudrava_test not found
"
Thank you.

Steps to address your issue
Ensure that you are using the most recent stable version of Idea (currently 2021.3.2), Java and JavaFX (currently 17.0.2).
Discard your current project.
Create a new project.
Follow the instructions at Create a new JavaFX project provided by Idea on how to use their wizard.
If you follow the instructions exactly it should work.
You don't need to add "the Java FX lib" to the project manually.
The wizard will create a dependency in Maven or Gradle which includes the most common JavaFX modules.
You don't need to download or use the JavaFX SDK mentioned at openjfx.io.
You don't need to explicitly set any VM arguments such as --add-modules the wizard will create the a module-info.java file which references the modules.
Before proceeding any further, make sure that the basic generated project build and runs in your environment (according to the build and execution instructions documented by IntelliJ for the new JavaFX project wizard).
Using additional JavaFX modules
If you want to use additional JavaFX modules (e.g. javafx.media or javafx.web):
Add the additional modules manually to the maven or gradle build file.
Reimport the build file into the Idea project.
Add requires clauses form the modules to the module-info.java.
Making your application non-modular
Even if your application is made non-modular, you still need to have JavaFX modules on the module path as that is the only way the execution of JavaFX is supported.
If you don't want a modular application, you can delete the module-info.java file and manually add VM arguments for the module path to the JavaFX and an --add-modules switch.
I do not advise doing this step unless:
You have a good reason not to have a non-modular application (e.g. rely on 3rd party dependencies which do not integrate easily with the Java module system), AND
You have knowledge about how to make non-modular JavaFX applications.
Cause of the module find exception
The reason for your specific error:
java.lang.module.FindException: Module com.example.hudrava_test not found
is because you don't have module-info.java for a module with that name on the module path. Note that is not a JavaFX module name, but something you have specified. You have tried to run the application by specifying a class name within the non-existent module, e.g.
java --module-path <somepath> -m com.example.hudrava_test/com.example.hudrava_test.HelloApplication
You can find out further info about that in:
java.lang.module.FindException: Module not found.
However, you should not need to manually take the steps outlined in that answer, because, when you create a new project using the new JavaFX wizard, it will automatically create a module-info.java file and place your application's build output on the modulepath.
So the error was caused by something you did after creating the project with the wizard (I don't know what). When you create a new project, you should not have the error.
On module naming and underscores
The Jenkov module tutorial states:
A Java module name follows the same naming rules as Java packages. However, you should not use underscores (_) in module names (or package names, class names, method names, variable names etc.) from Java 9 and forward, because Java wants to use underscore as a reserved identifier in the future.
It is recommended to name a Java module the same as the name of the root Java package contained in the module - if that is possible (some modules might contain multiple root packages).
So, it is inadvisable to have underscores in either your module or your package name.
More info on module naming suggestions is provided in:
How should I name my Java 9 module?

Using jlink with automatic modules

I have an explicit modular project which is dependent on an automatic module; e.g. on java.activation. Is it still possible to use jlink?
See this module-info.java:
module hello {
requires java.activation;
}
Then jlink can't add the module:
$ jlink --module-path target/modules --add-modules hello --output target/jlink
Error: automatic module cannot be used with jlink: java.activation from file:///C:/Development/jlinkExample/target/modules/javax.activation-api-1.2.0.jar
From my understanding, an automatic module would contain the whole classpath anyway. So I guess there would be no benefit to creating a runtime image with jlink?
See also: What is an automatic module?
Are there any possibilities to circumvent this issue? Maybe generating a module-info.java for those dependencies?

From my understanding an automatic module would contain the whole
classpath anyway, so I guess there would be no benefit in creating a
runtime-image with jlink?
No, automatic modules would not contain the whole classpath. In fact, the artifacts which are not explicitly defined as modules(contain module-info.java) but are found on the modulepath are treated as automatic modules to bridge the gap between explicit modules and the classpath code.
Are there any possibilities to circumvent this issue, maybe generating
a module-info for those dependencies?
Yes, you can either create a module-info.java with jdeps or use plugins like moditect to generate module-info for the module and inject it in your existing JAR.
Once the artifact(JAR) has an explicit module declaration, jlink should accept it without failure.

Java 9, Jigsaw and automatic modules

Java 9 / 10. I have been struggling with a simple project for more than a week.
As you can see in the picture, I want to use commons-collections as an automatic module (I have tried to add it with maven but that did not work out well).
So, I have red that I need to put the jar onto the module-path. Where does IntelliJ take this modulepath from? How can I tell the IDE to add commons-collections into the project so that
1. the compiler can find it at compile time and
2. Maven can find it at build time?
Anyone can help?
EDIT:
I have tried to add it in the project-structure dialog as a module dependency in all kinds of different combinations. I have literally tried hundreds of things, moved the jar around in the structure and I cannot find a simple enough doc to tell me how to do this.
I have used compiler options to add "--module-path automatic" (module specific and general compile options) in order to make IDEA find the thing and let Java make an automatic module out of it.

You need to add a library entry first, to make it available under Modules:
Step 1: Add a library (Add -> Java -> jar file)
Step 2: Select the module (remember to click "Apply")
After that, the module-info.java file will be successfully validated:

Intellij uses a module path if you run a program from an (intellij) module containing module-info.java, otherwise it will use a classpath.
I tried importing common4 as a module, it does seem to work for me, but I had to use a different 'requires' argument as compared to yours. Your 'requires' is 'commons.collections4', mine is 'org.apache.commons.collections4' (check the commons4 manifest entry for the highlighted Automatic-Module-Name and use that instead).
If the Automatic-Module-Name is missing from the commons4 manifest (it is absent from version 4.1 and earlier), Java may not detect the jar as a module if the name contains digits or illegal characters. Some maven repository jars therefore will not work and intelli will not see those jars as modules.
You can also check for a bad filename by using the following command:
jar --file=/path/to/jar --describe-module
If the command fails, it's likely that the jar does not have an Automatic-Module-Name entry and that the filename is poorly named.
ok
jar --file=C:\temp\jigsaw1-1.0.jar --describe-module
bad
jar --file=C:\temp\jigsaw1.0.jar --describe-module`
'jigsaw1.0: Invalid module name: '0' is not a Java identifier'
Some maven jars may therefore fail to be detected as modules as they tend to look similar.

How to run Java 9 application with classpath rather than module path in IDEA?

When I run a main class in IDEA, it puts the module and its dependencies on a module path. Is it possible to change it to a classpath?

If you don't define a module-info, IDEA would set the application and your dependencies on the classpath. Since you have a module-info it's an explicit module so it has to be on the module path. Normally you would handle your dependecies now as automatic-modules.
Howsoever, your dependencies at least have a good reason to be on the classpath. We discussed that here Why Java 9 does not simply turn all JARs on the class path into automatic modules?
For example, mymodule depends on an automatic-module which however needs a jar that can't become an automatic-module yet. On commandline it would like this:
java -cp legacy.jar -p "mymodule.jar;automodule.jar;" -m mymodule/com.example.mymodule.Application
IMO intellij doesn't currently support that. As a workaround to run the entire application on the classpath at least, you could rename the model-info for disabling/not to be a jigsaw-module for a moment.

To answer the question, the heuristic IDEA uses to run an application with a module path is currently slightly off (IDEA 2018.01). It apparently takes more into consideration than it should.
See IDEA-187390 and IDEA-193714 for details.
So if your current project does not have a module-info file and you still end up with a module path the current case that I know is that you are running the main class from a dependency. Just build a small wrapper inside your project and run the main class from there, that brings you back to the classpath.