Understanding errors with JPMS modules

Question

I am having a rough time deciphering what these errors mean, let alone even begin to resolve them. I am trying to use java platform modules (using jdk 14) with a simple "gradle-based, multi-module" project (everything works perfectly fine with jdk 8). The project makes use of spring-boot and spring-data-jdbc. Actually my core dependencies are

implementation 'org.springframework.boot:spring-boot-starter-data-jdbc'
implementation 'org.springframework.boot:spring-boot-starter-freemarker'
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.projectlombok:lombok'

While I was adding module-info.java to each project source root, my IDE (intellJ) was very kind to give me hints of what modules to export/require, and all looked good until I tred to compile.

I am including a git repo link here to the project that's th topic of this question - https://github.com/m41na/todo-modules-demo

If you have come across these (or similar) issues, could you please shed some light on how you were able to resolve them?

error: the unnamed module reads package org.springframework.data.jdbc.core.convert from both spring.data.jdbc and spring.data.relational
error: module spring.context reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot.starter.data.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot.starter.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.data.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot.starter reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.tx reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot.autoconfigure reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.aop reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.expression reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
the unnamed module reads package org.springframework.data.jdbc.core.convert from both spring.data.jdbc and spring.data.relational

error: module spring.core reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.boot.starter.logging reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module logback.classic reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module org.apache.logging.slf4j reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.context reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module jul.to.slf4j reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module org.slf4j reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.boot.starter.data.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module java.annotation reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.boot.starter.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module org.yaml.snakeyaml reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.jcl reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.data.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module logback.core reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
error: module spring.beans reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.boot.starter reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module spring.data.relational reads package org.springframework.data.jdbc.core.convert from both spring.data.jdbc and spring.data.relational
module spring.jdbc reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

error: module spring.data.commons reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc
module spring.tx reads package org.springframework.data.jdbc.core.convert from both spring.data.relational and spring.data.jdbc

Answer 1

TL;DR — I've solved your split packages errors in this clone of your project using the mrJar Gradle plugin ¹ .

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The long-winded answer

„ …I am having a rough time deciphering what these errors mean… “

Welcome to the world of split packages …

„ …'Split packages' is an old Java term where two packages having the same name exist in different libraries/applications. Java 9 does not allow split packages in different modules for the reason of the reliable configuration… “

That quote's from this blog .

„ …If you have come across these (or similar) issues… “

As several other Stack Overflow questions attest, split packages are an inevitability for anybody structuring their projects as JPMS modules.

„ …could you please shed some light on how you were able to resolve them?… “

Referring back to the TL;DR , I've resolved your project's split packages issue by applying the plugin I proposed. Download and build the demo to examine the results.

As I mention in that demo's documentation, Java 14 ⁺ support will be added to that plugin within the next day or two. As soon as it is, I will update the demo and edit this answer. But I figured rather than wait until then, you ( and other interested lurkers ) could benefit today from version 0.0.16's JDK 13 support.

Another solution I recently proposed is an implementation of Mark Reinhold's suggested „ Bridges to the class path “ approach. Numbers 2 and 3 that I mentioned in the comments take that approach. But personally I prefer the plugin approach. It's a lot easier and is way less effort.

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^{1 I have it on good authority that the mrJar plugin is in the process of being upgraded with JDK14+ support. Release of v0.0.17 is expected to be announced within the next 1-2 days.}