The current toolchain setup requires either two or three versions of the JDK plus a toolchains.xml Maven configuration. While this setup was sufficient to introduce support for Java 9+ APIs, it has made development slower and more difficult. Some problems include:
- Any module that depends on a java9 piece breaks incremental compilation; Maven recompiles the entire module every time! This makes it tedious to use mvn test on individual tests.
- IDEs have difficulty importing and executing toolchain-based Maven projects
- Contributors have a fairly esoteric hurdle to jump over now to contribute to Log4j
- As Java continues its release cadence of two releases a year, this makes it harder to test or develop Log4j on newer JDKs. This has become a more obvious problem ever since IDEs like IntelliJ switched from Java 8 to Java 11 as the default JDK.
To improve this situation, I propose the following build changes to simplify the scenario:
- Require Java 11 to compile everything.
- Introduce the animal-sniffer and enforcer Maven plugins to ensure that modules aren't unintentionally using or linking to Java APIs added in versions 9+
- Fix log4j-jmx-gui to use the jdk.jconsole module instead of linking to tools.jar from the JDK.
- Find a better multirelease pattern as documented here: https://maven.apache.org/plugins/maven-compiler-plugin/multirelease.html
This should result in a build that creates Java 8 compatible artifacts but requires Java 11 and only Java 11 to build, therefore significantly simplifying development environment setup for this project.