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Modules, Modules, Everywhere!

February 24, 2021

Project 🧩 sormuras/modules

Since August 2018, I have been compiling an overview of Java modules uploaded to Maven Central at

This overview is generated by the Scanner program and it is based on the results of the modulescanner that is run on Sonatypes hardware on every uploaded JAR file and stored in an AWS S3 bucket, setup together with the AdoptOpenJDK team at their #java9plusadoption Slack channel. Some of those uploaded JAR files are Java modules. They are the interesting subjects of this overview as they contain a module-info.class, a compiled module descriptor with a stable name and an explicit API their author(s) comitted to.

Let us start with looking at the raw numbers. As of today (February 18, 2021) the scan report reads:

Scanning 72598 files in bucket...
  5,204,605 lines
  2,020,116 distinct scan lines
    204,617 artifacts
    189,650 JAR files are plain
     10,276 JAR files with Automatic-Module-Name
      4,691 JAR files with module-info.class
      3,779 distinct modules
      2,900 unique modules
  • Over 2 (out of 5) million distinct lines were read from 72,598 CSV files downloaded from the S3 bucket. Somebody should reduce the 3 million lines overhead sometime.
  • 204,617 JAR file artifacts were analyzed, with
    • the vast majority of 189,650 JAR files were plain old JAR files,
    • 10,276 of them contained an Automatic-Module-Name manifest entry, and
    • 4,691 of them contained (at least one) module-info.class file.
  • Out of the 4,691 Java modules only 3,779 distinct modules could be filtered out. Due to wrong repackaging/shadowing of 3rd-party libraries like ASM or Log4J, there are already many unintended modules, I like to call them impostor modules, published at Maven Central. If Java modules names were treated as first-class library properties one could search Maven Central Repository for org.objectweb.asm, org.apache.logging.log4j, or other module names of well-known and often shadowed libraries to see many hits for various GroupIDs.
  • Out of the 3,779 distinct modules, I selected 2,900 unique modules by applying a filter comparing module names to the their Maven Group identifiers.

Unique Java Modules

I consider a Java module to be unique on Maven Central

  • if it is an explicit module with a compiled module descriptor,
  • and if its module name starts with its Maven Group identifier or a well-known alias.

Here are some examples of unique modules, showing their module names and Maven Group:Artifact identifiers:

Module Group ID : Artifact ID
ch.qos.logback.core ch.qos.logback:logback-core
ch.qos.logback.classic ch.qos.logback:logback-classic
java.xml.bind javax.xml.bind:jaxb-api
net.bytebuddy net.bytebuddy:byte-buddy
net.bytebuddy.agent net.bytebuddy:byte-buddy-agent
org.apache.logging.log4j org.apache.logging.log4j:log4j-api
org.junit.jupiter org.junit.jupiter:junit-jupiter
org.junit.jupiter.api org.junit.jupiter:junit-jupiter-api
org.junit.jupiter.engine org.junit.jupiter:junit-jupiter-engine
org.slf4j org.slf4j:slf4j-api

Well-known aliases for Maven Group identifiers are defined as:

String computeMavenGroupAlias(String group) {
  return switch (group) {
    case "com.fasterxml.jackson.core" -> "com.fasterxml.jackson";
    case "com.github.almasb" -> "com.almasb";
    case "javax.json" -> "java.json";
    case "net.colesico.framework" -> "colesico.framework";
    case "org.jetbrains.kotlin" -> "kotlin";
    case "org.jfxtras" -> "jfxtras";
    case "org.openjfx" -> "javafx";
    case "org.ow2.asm" -> "org.objectweb.asm";
    case "org.projectlombok" -> "lombok";
    case "org.swimos" -> "swim";
    default -> group.replace("-", "");

...which also permits Maven Group identifiers to contain - characters, hence matching to module names starting with org.foobar.

These aliases yield more hits increasing the number of unique modules. For example:

Module Group ID : Artifact ID
com.fasterxml.jackson.core com.fasterxml.jackson.core:jackson-core
com.fasterxml.jackson.annotation com.fasterxml.jackson.core:jackson-annotations
com.fasterxml.jackson.databind com.fasterxml.jackson.core:jackson-databind
com.fasterxml.jackson.kotlin com.fasterxml.jackson.module:jackson-module-kotlin
kotlin.stdlib org.jetbrains.kotlin:kotlin-stdlib
kotlin.reflect org.jetbrains.kotlin:kotlin-reflect
kotlin.stdlib.jdk7 org.jetbrains.kotlin:kotlin-stdlib-jdk7
kotlin.stdlib.jdk8 org.jetbrains.kotlin:kotlin-stdlib-jdk8
lombok org.projectlombok:lombok
org.objectweb.asm org.ow2.asm:asm
org.objectweb.asm.tree org.ow2.asm:asm-tree
org.objectweb.asm.tree.analysis org.ow2.asm:asm-analysis
org.objectweb.asm.util org.ow2.asm:asm-util

Find a daily updated listing of unique modules at:

Find module com.github.sormuras.modules also attached as an executable JAR and ToolProvider in the assets of releases/tag/0-ea. Stable versions of it are published to releases; with releases/latest pointing to the latest stable release.

Bear in mind that the raw and filtered numbers may alter with changes made to the Scanner and the modulescanner programs. This also goes for changes made to the Maven Group Alias function.

More Modules

The doc directory of the sormuras/modules project hosts lists of Maven Group:Artifact coordinates in 📜 text files. They are taken as an input of the scan process. The Scanner generates overview tables showing the state of modularization for each Group:Artifact coordinate.

You will find the following summary at the start of each overview.

  • 🧩 denotes a Java module that contains a compiled module descriptor.
    It therefore provides a stable module name and an explicit modular API using exports, provides, opens and other directives.
  • ⬜ denotes an automatic Java module, with its stable module name derived from Automatic-Module-Name manifest entry.
    Its API is derived from JAR content and therefore may not be stable.
  • ⚪ denotes an automatic Java module, with its not stable module name derived from the JAR filename.
    Its API is derived from JAR content and therefore may not be stable.
  • ➖ denotes an unrelated artifact, like BOM, POM, and other non-JAR packaging types.
    It also denotes old JAR files, as the scan process can only evaluate artifacts that were deployed after mid August 2018.


📜 WatchList overview.

Compiled from WatchList.txt, which contains a community-curated list of Maven Group:Artifact lines.

Top 1000-2020


Top1000-2010.txt contains 1,000 Maven Group:Artifact lines sorted by download popularity as of December 2020. This list may include some non-JAR entries (pom, bom, ...). It also contains entries that were not updated since August 2018.

Top 1000-2019


Top1000-2019.txt contains 1,000 Maven Group:Artifact lines sorted by download popularity as of December 2019. This list also includes non-JAR entries (pom, bom, ...). It also contains entries that were not updated since August 2018.

Summary And Outlook

Java modules are here to stay. Their number is increasing steadily.

Taking numbers of the Top1000-2020 list as reference, I hope to see 20% Java modules here next year. This can be achieved by a) filtering out more unrelated artifacts and b) adding module descriptors to more libraries.

Icon Numbers Description
🧩 116 (11,6%) Java modules (module descriptor with stable name and API)
254 (25,4%) Automatic Java modules (name derived from JAR manifest)
474 (47,4%) Automatic Java modules (name derived from JAR filename)
156 (15,6%) Unrelated artifacts (BOM, POM, ... or not recently updated)

So... when will you publish your first Java module to Maven Central? 🙂



  • Christian Stein

    Christian is an open source software developer who is programming with Java since 1998. He has a passion for automated testing and joined the core JUnit Team in 2017, is ... Learn more

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