Switch-Java (PowerShell)

Introduction

A simple, robust, and maintainable PowerShell utility to switch between multiple installed Java JDK versions on Windows. It updates JAVA\_HOME and ensures your PATH points to %JAVA\_HOME%\\bin, avoiding conflicts between JDK installations. Designed for developers working across projects that require different Java versions (e.g., 8, 11, 17, 21, 25).

Default JDK locations in this repository follow my own setup:

`D:\\Ignacio\\Aplicaciones\\Java JDKs\\<VERSION\_NAME>`

Example: `D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 21`

Features

• Switch Java version with one command (-Version 8|11|17|21|25).
• Write to User or Machine scope (-Scope User|Machine).
• Idempotent PATH management: ensures only one %JAVA\_HOME%\\bin entry and cleans conflicting JDK bin paths.
• Validation of target JDK (checks bin\\java.exe and bin\\javac.exe).
• Interactive mode for quick selection.
• Dry run mode to preview changes without applying them.
• Optional external config file jdk-versions.json for easy maintenance.
• Clear, informative output with robust error handling.

How it works

1. Configuration:

   • The script ships with a built-in map of JDK versions → installation directories:

     • 8 → D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 8
     • 11 → D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 11
     • 17 → D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 17
     • 21 → D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 21
     • 25 → D:\\Ignacio\\Aplicaciones\\Java JDKs\\Java 25

   • If a jdk-versions.json file exists next to the script, it will override these paths.

2. Switching:

   • When you run -Version <number>, the script resolves aliases (e.g., Java 17, jdk-21) to the major version (e.g., 17, 21).
   • It validates the target path by checking for bin\\java.exe and bin\\javac.exe.
   • It sets JAVA\_HOME at the selected scope and updates PATH so that %JAVA\_HOME%\\bin is at the beginning.
   • It removes direct JDK bin paths from PATH to prevent conflicts.
   • It broadcasts an environment change event (WM\_SETTINGCHANGE) so GUI apps can pick up the new variables (some may still require reopening).

3. Current session update:

   • The script also updates JAVA\_HOME and PATH for the current PowerShell session, allowing you to use the new version immediately without opening a new terminal. The -Current flag will display both java --version and javac --version outputs.

How to execute the script

1. Clone or download the Git repository from GitHub
2. Open a PowerShell instance and run it with administrator privileges.
3. Navigate to the script folder and run one of the following:

# Switch to JDK 21 at Machine scope (requires Admin)
PS> .\\Switch-Java.ps1 -Version 21 -Scope Machine

# Switch to JDK 8 at User scope
PS> .\\Switch-Java.ps1 -Version 8

# Interactive menu
PS> .\\Switch-Java.ps1 -Interactive

# Show current JAVA\_HOME and java/javac versions
PS> .\\Switch-Java.ps1 -Current

# Preview changes without applying (now supports 17 too)
PS> .\\Switch-Java.ps1 -Version 17 -DryRun

Execution policy note: If you haven't enabled script execution from external sources, run:

# 1) Set the ExecutionPolicy to the value `RemoteSigned` for the `CurrentUser` scope
Set-ExecutionPolicy -Scope CurrentUser -ExecutionPolicy RemoteSigned
 
# 2) Signed the Powershell Script locally to allow the execution of the commands and the other related files
Get-ChildItem -Path "<YOUR\_DESTINATION\_FOLDER>" -Recurse | Unblock-File

Good Practices Implemented

• Scoped writes: Choose User or Machine scope with explicit admin checks.
• Idempotent PATH updates: No duplicates; %JAVA\_HOME%\\bin is guaranteed to be present once.
• Conflict cleanup: Removes direct JDK bin paths that can shadow %JAVA\_HOME%\\bin.
• Validation before switching: Ensures java.exe and javac.exe exist.
• Clear error messages and dry-run mode for safe changes.
• Interactive UX and helpful usage banner.
• Optional JSON config for easy maintenance without editing the script.
• Environment change broadcast so desktop apps can pick up updates.

Notes & Limitations

• Admin rights are required to modify Machine scope environment variables.
• Some applications or terminals may need to be restarted to pick up changes.
• PATH cleanup is conservative. If you have custom JDK paths that should remain, consider using the optional jdk-versions.json and ensure your other PATH entries are not mistakenly matching the cleanup patterns.
• The script targets Windows (PowerShell on Windows). It isn't intended for WSL or Linux/macOS.
• JDK install directory names must match your actual setup. Adjust either the built-in map or create jdk-versions.json to reflect exact paths.

License

This project is licensed under the GNU General Public License v3.0 (GPL-3.0).

By using, modifying, or distributing this software, you agree to the terms defined in the GPL-3.0 license. In summary:

You are free to run, study, modify, and share the software.

If you distribute modified versions of the program, the result must also be licensed under GPL-3.0, ensuring the same freedoms for users.

Any redistributed version—modified or unmodified—must include a copy of the license and appropriate copyright notices.

No warranty is provided, as explicitly described in the license.

For the full legal text, refer to the official GPL-3.0 license:

https://www.gnu.org/licenses/gpl-3.0.en.html