How to add a non-modular Maven dependency to the module path as an automatic module?

Question

Lets say we would like to build a simple Java 11 modular Maven project with a single non-modular dependency org.json:json (picked at random for the sake of a practical example).

Project structure:

project
|-- pom.xml
`-- src
    `-- main
        `-- java
            |-- foo.bar.project
            |   `-- foo
            |       `-- bar
            |           `-- project
            |               `-- Foo.java
            `-- module-info.java

Foo.java:

package foo.bar.project;

import org.json.JSONObject;

public class Foo {
    static JSONObject o = new JSONObject();
}

module-info.java:

module foo.bar.project {
}

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/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>foo.bar</groupId>
  <artifactId>project</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.release>11</maven.compiler.release>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.json</groupId>
      <artifactId>json</artifactId>
      <version>20200518</version>
    </dependency>
  </dependencies>

  <build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.1</version>
          <executions>
            <execution>
                <goals>
                    <goal>compile</goal>
                </goals>
                <id>compile</id>
            </execution>
          </executions>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

---

My question is how to tell Maven to put org.json on the module path as an automatic module. By default, Maven places non-modular jars on the classpath as unnamed modules.

As it stands, running mvn clean compile fails with:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project project: Compilation failure
[ERROR] <PathToProject>/src/main/java/foo.bar.project/foo/bar/project/Foo.java:[3,11] package org.json is not visible
[ERROR]   (package org.json is declared in the unnamed module, but module org.json does not read it)
[ERROR]
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

---

System info:

Apache Maven 3.6.0 (97c98ec64a1fdfee7767ce5ffb20918da4f719f3; 2018-10-24T20:41:47+02:00)
Maven home: C:\Tools\apache-maven-3.6.0
Java version: 11.0.1, vendor: Oracle Corporation, runtime: C:\Program Files\Java\jdk-11.0.1
Default locale: sl_SI, platform encoding: UTF8
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"

Answer 1

Ii find the message

[ERROR] (package org.json is declared in the unnamed module, but module org.json does not read it)

strange, it should have read "..but module foo.bar.project does not read it".

Then you would have found that you need to place a directive in module-info.java such as:

requires org.json;