Develop Reference

Not finding automatic modules when compiling Java Application

I have a large multi module (100s) Java project and have been experimenting with adopting java module support. This is using Java 17 (temurin), gradle 7.6, and IntelliJ 2022.3.
I have hit a couple of stubborn errors with java modules where the module cannot be found.
I have one project which has some java code that uses plexus ie:
import org.codehaus.plexus.util.Base64;
...
byte[] encodedAuthorizationString = Base64.encodeBase64(authorizationString.getBytes(StandardCharsets.US_ASCII));
It has a gradle dependency
implementation 'org.codehaus.plexus:plexus-utils'
This has a version constraint in our main build.gradle (just salient lines included):
plexusVersion = '3.5.0'
implementation("org.codehaus.plexus:plexus-utils:${plexusVersion}")
Prior to adding module support this is working fine.
Now, with a module-info.java:
module egeria.open.metadata.implementation.adapters.open.connectors.rest.client.connectors.spring.rest.client.connector.main {
requires egeria.open.metadata.implementation.adapters.authentication.plugins.http.helper.main;
requires egeria.open.metadata.implementation.adapters.open.connectors.rest.client.connectors.rest.client.connectors.api.main;
//requires egeria.open.metadata.implementation.adapters.open.connectors.rest.client.connectors.rest.client.factory.main;
requires egeria.open.metadata.implementation.frameworks.open.connector.framework.main;
requires plexus.utils;
requires org.slf4j;
requires spring.core;
requires spring.web;
exports org.odpi.openmetadata.adapters.connectors.restclients.spring;
}
I am getting a compile error
Task ':open-metadata-implementation:adapters:open-connectors:rest-client-connectors:spring-rest-client-connector:compileJava' is not up-to-date because:
Task has failed previously.
The input changes require a full rebuild for incremental task ':open-metadata-implementation:adapters:open-connectors:rest-client-connectors:spring-rest-client-connector:compileJava'.
Full recompilation is required because no incremental change information is available. This is usually caused by clean builds or changing compiler arguments.
Compiling with toolchain '/Library/Java/JavaVirtualMachines/temurin-19.jdk/Contents/Home'.
Compiling with JDK Java compiler API.
/Users/jonesn/IdeaProjects/egeria/v4/open-metadata-implementation/adapters/open-connectors/rest-client-connectors/spring-rest-client-connector/src/main/java/module-info.java:6: error: module not found: plexus.utils
requires plexus.utils;
^
1 error
This is despite the fact, that having downloaded the jar file, the automatic module name looks to be what I am using ie:
jar --file=/Users/jonesn/Downloads/plexus-utils-3.5.0.jar --describe-module
No module descriptor found. Derived automatic module.
plexus.utils#3.5.0 automatic
requires java.base mandated
contains org.codehaus.plexus.util
contains org.codehaus.plexus.util.cli
contains org.codehaus.plexus.util.cli.shell
contains org.codehaus.plexus.util.dag
contains org.codehaus.plexus.util.introspection
contains org.codehaus.plexus.util.io
contains org.codehaus.plexus.util.reflection
contains org.codehaus.plexus.util.xml
contains org.codehaus.plexus.util.xml.pull
I am seeing the same error with kafka-clients
For most other code, including those libraries without full module support, all is good....
tried various compilers, such as openjdk 17 & temurin 19
built at cli & within IntelliJ
I was expecting this module to resolve ok
I have also reviewed Java 9 automatic modules not found but note that other automatic modules (including org.slf4j) are working just fine
I should add that I could refactor this code to use java.util.Base64 (probably makes sense)... but I'm still confused as to why the module error, which I also see in another project with 'kafka.clients'

Getting NoClassDefFoundError -> com/sun/jna/platform/win32/Psapi with Eclipse

My program relies on the following code to get available system memory:
import oshi.SystemInfo;
import oshi.hardware.HardwareAbstractionLayer;
SystemInfo si = new SystemInfo();
HardwareAbstractionLayer hal = si.getHardware();
// Next line throws exception: NoClassDefFoundError -> com/sun/jna/platform/win32/Psapi
long availableBytes = hal.getMemory().getAvailable();
double availableMegabytes = ((double) availableBytes) / 1048576;
double availableGigabytes = ((double) availableMegabytes)/1024;
Update: After deleting every occurrence of oshi-core from every project in Workspace (to remove possibility of transient conflict dependency - only 4.2.1 is left). Now the error I get is -> java.lang.NoClassDefFoundError: com/sun/jna/platform/win32/VersionHelpers
In pom.xml I've added oshi-core dependency - I've tried almost every version starting from version 3.4.0 to latest version 4.2.1 and they all result in the same error.
I realize oshi-core relies on jna and jna-platform. In Dependency Hierarchy I see both have resolved (compiled) to version 5.5.0.
What is causing this error and how can it be solved?
Thanks!
P.S
I've seen some other threads with similar error but could not find any thread with this exact problem (missing com/sun/jna/platform/win32/Psapi)

While you've pointed out in your comments that you think the latest version of JNA is being resolved, the errors indicate that your project does not have the most recent version of jna-platform (or possibly it has multiple versions linked on the classpath). This is nearly always the case for NoClassDefFoundError and while you're troubleshooting in the right direction, evidence indicates there's an old jna-platform version in your project somewhere.
The com.sun.jna.platform.win32.VersionHelpers class is in jna-platform version 5.3.0 and newer. The GetPerformanceInfo() method required for the method call giving you the error is in the com.sun.jna.platform.win32.Psapi class is in jna-platform version 4.3.0 and newer. If your classloader can't find these classes, then you don't have the correct jars linked to your project -- or you have incorrect jars linked alongside the correct ones.
Maven resolves dependencies by level... first it does all the dependencies you list in your POM (in order), then the transitive dependencies of those projects (in order) and so on. Ensuring the most recent version of JNA is used can be enforced by either (or both) of:
Specify oshi-core dependency earlier in your list of dependencies
in your POM, specifically, before any project that depends on an
earlier version of JNA.
Explicitly specify the jna and
jna-platform versions (5.5.0) in your top-level POM.
Also, in Eclipse, be sure to go through the menus to Update Maven Project to ensure your dependencies are in sync after changes in the POM.
It's possible that your local repository is not downloading the updated jar, in which case you can purge it (or just delete any JNA artifacts, or everything, from C:\Users\<username>\.m2\repository and let it rebuild.)
Also check the classpath in Eclipse. If you have manually added dependencies (e.g., to JNA) before setting up your POM to get them from Maven, you could be using those.
If the above hints do not resolve your problem, please post the contents of the dependencies section your pom.xml file so we can provide additional advice.

Seems oshi-core relies on internal undocumented features of the Sun / Oracle JVM, and you're running on a different and/or newer JVM that doesn't have that undocumented feature anymore. That's the risk of using undocumented features.
Get a newer/other version of oshi-core that supports the version of the JVM you're using, or switch to use a JVM that oshi-core supports.

Unable to derive module descriptor: Provider {class X} not in module

I am getting this error message when I try to compile my new modularized Java 11 application:
Error occurred during initialization of boot layer
java.lang.module.FindException: Unable to derive module descriptor for C:\Users\inter\.m2\repository\xalan\xalan\2.7.2\xalan-2.7.2.jar
Caused by: java.lang.module.InvalidModuleDescriptorException: Provider class org.apache.bsf.BSFManager not in module
This appears to be an issue from a dependency of a dependency. I can't even find which module is pulling it in so I can update it.
I am using openjdk 11.0.2, IntelliJ 2018.3.4, Maven
Any advice how I can troubleshoot or fix this? I have found very little documentation on this issue.

Xalan
I had a look at their bug tracker following their index page and wasn't able to find this reported and not sure how actively is the library being maintained either.
General Explanation
Just to explain what has caused the issue in your code, I would share a screenshot and then try to add details around it.
So within the JAR that for version 2.7.2, there are service declarations (META-INF/services) which include org.apache.xalan.extensions.bsf.BSFManager as one of them. The service file here has to indicate the Provider thereby for itself and the class is supposed to be present on the modulepath to be resolved for reliable configuration of modules.
In this case for the module xalan(automatic module), the service listed doesn't have the provider class packaged within the dependency itself. (See the package org.apache, it doesn't further have package bsf and the class BSFManager thereby. Hence the exception as you get.
Short term hack
One of the tweaks to get that resolved would be to get update the library jar (patch it) and get rid of the service file if you're not using it. Or to add the provider copied from the corresponding artifact.
If you don't directly depend on this artifact or its parent dependencies, you can let those remain on the --classpath and get resolved as an unnamed module for your application.
Long term solve
An ideal way would be to report this to the maintainers and getting it resolved. It depends though on how actively are they maintaining it e.g. the last release for xalan was almost 5 years back, might just want to look for an actively participated alternative in my opinion.

I tried to install update for TestNG in eclipse:
"Help -> Check for updates -> deselect all and select TestNG check box. Then
install latest version i installed the version which starts with 7.2.0.
It fixed the issue for me.

How to define qualified exports to unknown modules?

I have a Maven project with two Maven modules A and B. A contains the following Java module definition:
module A {
exports internal.util to B;
exports external.A;
}
B contains the following Java module definition:
module B {
requires A;
exports external.B;
}
When I build the project, I get an error:
[WARNING] module-info.java:[16,106] module not found: B
Module B exists but because Module A is compiled before B and does not depend on it, the compiler has no way of knowing that. Because I configured the compiler to treat warnings as errors (-Werror), the build fails.
Seeing as I want to keep treating warnings as errors, what is the best way to resolve this problem?
Is there a way to hint to the compiler that this module will be declared in the future?
Is there a way to suppress all warnings of this type?

I figured out a workaround by scanning through the JDK 11 source-code: -Xlint:-module. I am still open to a better solution if someone finds one.
UPDATE: An alternative is to use --module-source-path as demonstrated by https://stackoverflow.com/a/53717183/14731
Thank you Alan Bateman for pointing me in this direction!

As I could infer from the question, your scenario is such that both the module A and B co-exists and the module A does not depend on the module B.
From a module system prospect, since A makes a qualified export to the module B, a warning is thrown if the module B is not resolved on the modulepath while you build A.
On IntelliJ-IDEA I could fix such an issue by adding a dependency of module B to the module A without any declaration changes. Though using the Maven framework, I couldn't imagine something without a cyclic dependency here, maybe the suggestion by khmarbaise could help.
Note: An alternate way to fix this though could also be to disable such warnings using the command-line arg :
-Xlint:-exports
Or as Alan points out for correction
-Xlint:-module
Thinking out loud, that would be since, the warning is a result of a qualified export, but about a module not found.
Useful: You could find the details over these command line args with javac command.

warning: unknown enum constant Status.STABLE

In the quest to solve this and somehow that, I was trying out to create packages to subdivide main and test classes and then to make use of compiler with added modules to execute the unit-tests. Not a very good way agreed, but just a hypothetical structure for now.
Few open questions as I proceeded further were:-
Add a JDK9 based module to the project.
Add JUnit5 to the classpath using IntelliJ's shortcut. (lib folder) [junit-jupiter-api-5.0.0.jar]
Q. Note that it brings along the opentest4j-1.0.0.jar to the lib/ folder. Why is that so, what is the other jar used for?
Add the classes and generate some tests method correspondingly.
Compile the sample project (shared just to draw a picture of the directory structure in use) using the command
javac --module-path lib -d "target" $(find src -name "*.java")
Results into warnings as -
warning: unknown enum constant Status.STABLE
reason: class file for org.apiguardian.api.API$Status not found
warning: unknown enum constant Status.STABLE
2 warnings
Note:-
I find the usage of junit-jupiter suspicious since if I comment out the code using JUnit and execute the same command, things seem to be working fine.
Libraries/Tools used if that might matter:-
junit-jupiter-api-5.0.0 with
Java version "9" (build 9+181)
IntelliJ 2017.2.5
Q. What could be a probable cause to such a warning? Moreover, I am unable to find the API.Status in my project and outside the project classes as well.

The compilation warning can simply be ignored. Moreover, it won't be appearing anymore starting with the version 5.1.0 (currently in development). It is all explained in Release Notes:
In 5.0.1, all artifacts were changed to have an optional instead of a mandatory dependency on the #API Guardian JAR in their published Maven POMs. However, although the Java compiler should ignore missing annotation types, a lot of users have reported that compiling tests without having the #API Guardian JAR on the classpath results in warnings emitted by javac that look like this:
warning: unknown enum constant Status.STABLE
reason: class file for org.apiguardian.api.API$Status not found
To avoid confusion, the JUnit team has decided to make the dependency to the #API Guardian JAR mandatory again.
For reference also see:
Remove compile dependency on apiguardian-api in Maven POMs
Reintroduce compile dependency on apiguardian-api in Maven POMs

1) opentest4j
opentest4j is a transitive dependency of junit-jupiter-api. See the dependency graph:
+--- org.junit.jupiter:junit-jupiter-api:5.0.1
+--- org.opentest4j:opentest4j:1.0.0
\--- org.junit.platform:junit-platform-commons:1.0.1
2) unknown enum constant Status.STABLE
You need to add following dependency: apiguardian-api.
For example in Gradle, you can do it via:
dependencies {
testCompile 'org.junit.jupiter:junit-jupiter-api:5.0.1'
testRuntime 'org.junit.jupiter:junit-jupiter-engine:5.0.1'
testCompileOnly 'org.apiguardian:apiguardian-api:1.0.0'
}
But overall, dependency is build-tool-independent, so you can do it in plain IDE without Gradle, or Maven.