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Using a Custom Java Version

This guide explains how to configure and use your own Java version (JDK/JRE) when building a profile in GML Backend.

1. Determine the Target Platform​

Go to the directory:


/srv/gml/data/GmlBackend/runtime/

Inside, you will find folders corresponding to different operating systems:


linux/
linux-i386/
mac-os/
mac-os-arm64/
windows-arm64/
windows-x64/  ← example
windows-x86/

⚠️ Select the folder that matches the system for which you are building the profile.
In this example, we will use windows-x64.

2. Prepare the Folder for Your Java​

Navigate to the chosen platform directory, for example:


/srv/gml/data/GmlBackend/runtime/windows-x64/

Create (or open, if it already exists) a folder:


java-runtime-gamma

3. Install Your Custom Java​

The java-runtime-gamma folder may already contain a preinstalled Java. To replace it with your version:

  1. Remove all existing files in this folder.
  2. Copy your JDK or JRE contents into this folder.
  3. Ensure the directory structure is correct and contains executable files (bin/java, bin/java.exe, etc.).

4. Set Permissions​

For Linux or other UNIX systems, set read and execute permissions only:

chmod 0555 java-runtime-gamma

This will result in the following permissions:

PermissionOwnerGroupOthers
R (Read)✅✅✅
W (Write)❌❌❌
X (Execute)✅✅✅

Permission code: 0555 Owner: root Group: root

✅ This protects your Java from accidental modification or deletion.

5. Alternative Method (Windows, without WSL)​

If you are on Windows 10/11 and not using WSL, you can apply similar restrictions via NTFS properties:

  1. Right-click the java-runtime-gamma folder → Properties → Security.
  2. Click Edit.
  3. For each group (e.g., Users, Administrators), check Deny for the Write permission.
  4. Click Apply → OK.

This is equivalent to chmod 0555 on Windows.

6. Verify the Setup​

After completing the steps, ensure that:

  • The java-runtime-gamma folder structure is correct.
  • All necessary executables (java, javac, etc.) are present.
  • Permissions are set properly.

Now, when building a profile for the corresponding platform (in this example — windows-x64), your custom Java version will be used.

7. Note for Other Platforms​

If you are building a profile for a different OS:

  • Simply replace windows-x64 in the paths with the appropriate folder, for example:

    • linux
    • linux-i386
    • mac-os
    • mac-os-arm64

✅ Outcome​

After completing this guide:

  • GML Backend will use your custom Java when building profiles.
  • The Java version is fully under your control.
  • Standard environment or bundled runtimes will not interfere.