Managing Multiple JDK Versions with jEnv

Developers often need to switch between different codebases that require different Java versions, especially with the six‑month release cycle of Java. jEnv is a tool that lets you manage multiple JDK installations and assign a specific JDK to each project without altering the JAVA_HOME environment variable.

Install jEnv on Linux or macOS (Windows users need WSL or a Bash emulator) following the instructions on the jEnv homepage. Then download a JDK (e.g., from AdoptOpenJDK) as a .tar.gz archive and extract it to a directory of your choice.

To make the new JDK known to jEnv, run jenv add /path/to/jdk-15+36/ . After adding, jenv versions will list all available JDKs, including the newly added 15 and openjdk64-15 .

jEnv supports both a global JDK (used when no local version is defined) and local JDKs (specific to a folder). Set the global JDK with jenv global 11 and verify it with jenv global . For a project, navigate to its directory and run jenv local 15 , which creates a .java-version file containing the version number.

When the .java-version file is present, any java command executed in that folder uses the specified JDK; otherwise, the global JDK is used. This mechanism allows different projects to run with different Java versions.

To make Maven use the jEnv‑configured JDK, enable the Maven plugin with jenv enable-plugin maven . After that, mvn -version will report the local JDK (e.g., Java 15). Similarly, enable the Gradle plugin with jenv enable-plugin gradle so Gradle automatically picks up the local JDK.

If the wrong Java version is still selected, enable the export plugin via jenv enable-plugin export to ensure JAVA_HOME is set correctly for wrapper scripts like ./gradlew or ./mvnw .

In conclusion, jEnv provides a convenient way to manage multiple JDKs across projects, allowing you to set the desired JDK per directory with jenv local <version> and avoid version conflicts in Java development.