March 7, 2025

Installing Java 21 on macOS Using jEnv: Best Practices & Troubleshooting

Introduction

Java 21 is the latest long-term support (LTS) release, bringing new features and enhancements for developers. Managing multiple Java versions on macOS can be cumbersome, but tools like jEnv simplify this process. In this guide, we will cover how to install Java 21 using jEnv, best practices, troubleshooting common issues, and alternative tools.

What is jEnv?

jEnv is a command-line tool for managing multiple Java versions on your system. It allows you to switch between different Java versions seamlessly, ensuring that each project runs with the correct Java version.

Key Features of jEnv:

  • Easily switch between installed Java versions
  • Works with different shells (Bash, Zsh, Fish)
  • Project-specific Java version management
  • System-wide or user-level Java configuration

Installing jEnv on macOS

Follow these steps to install jEnv on macOS:

1. Install jEnv via Homebrew

brew install jenv

2. Add jEnv to Your Shell

To ensure jEnv works properly, add it to your shell profile.

For Zsh (default in macOS):

echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.zshrc
echo 'eval "$(jenv init -)"' >> ~/.zshrc
source ~/.zshrc

For Bash:

echo 'export PATH="$HOME/.jenv/bin:$PATH"' >> ~/.bash_profile
echo 'eval "$(jenv init -)"' >> ~/.bash_profile
source ~/.bash_profile

3. Verify jEnv Installation

Check if jEnv is installed correctly by running:

jenv --version

Installing Java 21

To install Java 21 on macOS, follow these steps:

1. Install Java 21 Using Homebrew

brew install openjdk@21

2. Add Java 21 to jEnv

Find the installed Java path:

/usr/libexec/java_home -V

Once you locate Java 21’s path, add it to jEnv:

jenv add /Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home

3. Set Java 21 as Global or Local Version

To set Java 21 as the default version system-wide:

jenv global 21

For a specific project:

jenv local 21

To verify:

java -version

Best Practices for Using jEnv

  1. Always Restart Your Shell: After installing or updating jEnv, restart your terminal to apply changes.
  2. Use Local Version for Projects: Set Java versions per project to prevent compatibility issues.
  3. Check jEnv Doctor: Run jenv doctor to diagnose potential issues.
  4. Avoid Mixing Manual and Homebrew Installations: Stick to Homebrew for easier updates and maintenance.
  5. Keep Java Versions Updated: Regularly check for new updates using brew upgrade openjdk@21.
  6. Use jEnv Plugins: Enhance functionality by adding plugins like jenv enable-plugin export.

Troubleshooting Common Issues

1. jEnv Command Not Found

Solution: Ensure jEnv is correctly added to your shell profile and restart your terminal:

source ~/.zshrc  # or source ~/.bash_profile

2. Java Version Not Changing

Solution: Check if jEnv is properly managing Java:

jenv versions
jenv rehash

Make sure the correct version is set globally or locally.

3. Java Command Not Found

Solution: Ensure Java is installed and added to jEnv:

brew install openjdk@21
jenv add /Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home

4. jEnv Not Recognizing Java Installations

Solution: Run the following command to refresh Java installations:

jenv rehash
/usr/libexec/java_home -V

5. Homebrew Not Linking Java Correctly

If you see errors related to brew link:

brew link --force --overwrite openjdk@21

6. jEnv Not Working with IDEs (IntelliJ, VS Code, etc.)

If your IDE does not recognize the jEnv-managed Java version, configure it manually by pointing it to the correct path:

/Library/Java/JavaVirtualMachines/openjdk-21.jdk/Contents/Home

7. Permission Issues When Adding Java Versions

If you see permission errors while adding Java:

sudo chmod -R 755 /Library/Java/JavaVirtualMachines/openjdk-21.jdk

8. OpenJDK Performance Issues

If Java 21 feels slow, try enabling optimized JVM flags:

export JAVA_OPTS="-XX:+UseG1GC -XX:+UseStringDeduplication"

Upcoming Changes & Latest Techniques

1. Java 21 Features to Explore

  • Virtual Threads (Project Loom)
  • Record Patterns & Pattern Matching
  • Structured Concurrency
  • Generational ZGC (Improved Garbage Collection)

2. JEP (Java Enhancement Proposals) Roadmap

  • Future improvements include better native memory tracking and class-data sharing.
  • Follow updates at OpenJDK JEP Roadmap

3. Using SDKMAN! Instead of jEnv

SDKMAN! is gaining popularity as an alternative:

curl -s "https://get.sdkman.io" | bash
sdk install java 21-open

4. jEnv vs. asdf for Java Management

asdf is another alternative, especially if you manage multiple languages:

brew install asdf
asdf plugin-add java
asdf install java openjdk-21

Alternative Tools to jEnv

While jEnv is excellent, here are some other Java version managers:

  1. SDKMAN!

    • Best for managing SDKs and Java versions.
    • Installation: curl -s "https://get.sdkman.io" | bash
    • Read more: sdkman.io

  2. asdf

    • A universal version manager supporting multiple languages, including Java.
    • Installation: brew install asdf
    • Read more: asdf-vm.com

  3. Homebrew Versions

    • Directly install and switch Java versions via Homebrew.
    • Example: brew install openjdk@21 && brew unlink openjdk && brew link --force --overwrite openjdk@21

Conclusion

jEnv is a powerful tool for managing Java versions on macOS, making it easier to switch between different projects and environments. Following best practices ensures a smooth experience while avoiding common pitfalls. If you prefer alternatives, SDKMAN! and asdf are also great choices for managing Java versions efficiently.

Further Reading:

By following these steps and best practices, you can efficiently manage Java 21 and other versions on your Mac using jEnv. 🚀

Posted by