[MNG-5771] improved user-configurable core extensions mechanism

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.3.1
• Component/s: Class Loading
• Assignee: igorfie
• Reporter: Igor Fedorenko
• Created: 20/Feb/15 08:13
• Updated: 29/Nov/22 18:41
• Resolved: 20/Feb/15 13:09

Description

As of version 3.2.5 maven provides two mechanisms to contribute additional components to maven core runtime. It is possible to add component jars to $M2_HOME/lib/ext directory. It is also possible to specify component jars using -Dmaven.ext.class.path command line parameter. Neither of the mechanisms is user friendly. In both cases, the user is expected to manually locate and download all required jar file. In both cases, this has to be done on all systems where the extensions are needed. In both cases, all extra jars are loaded into single classloader so all extensions must agree of the same set of dependencies.

This jira is to track changes needed to make it possible to configure core extensions in terms of groupId/artifactId/version and share set of required extensions across multiple systems.

More specifically,

• introduce new ${maven.projectBasedir}/.mvn/extensions.xml descriptor to specify list of extensions. Initially, the descriptor will only allow specification of extension groupId/artifactId/version, but can be extended to support dependency includes/excludes mechanism and configuration parameters later

  <?xml version="1.0" encoding="UTF-8"?>
  <extensions>
    <extension>
      <groupId>...</groupId>
      <artifactId>...</artifactId>
      <version>...</version>
    </extension>
    <extension>...</extension>
    ...
  </extensions>
  

• change maven to read and load core extensions in separate class realms as part of plexus container setup.
• provide mechanism for extensions to declare exported artifacts and packages using META-INF/maven/extension.xml descriptor.

Issue Links

• is related to: MNG-5889 .mvn directory should be picked when using --file
• is related to: MNG-7609 Clarify documentation of extension descriptor
• relates to: MNG-5779 NoClassDefFoundError: org/slf4j/spi/LocationAwareLogger when generating javadoc during site reporting
• supercedes: MNG-5641 AbstractMavenLifecycleParticipant#afterSessionStart is never invoked
• links to: GitHub Pull Request #338