How do I specify the Java version in sbtopts?

To specify the Java version used by SBT (Simple Build Tool), you typically configure it through the sbtopts file. This file is used to pass JVM options to the SBT launcher. Here's how to do it:

1. Locate the sbtopts File:

- The sbtopts file is usually located in the same directory as your sbt executable or in the .sbt directory in your home directory. For example:

~/.sbt/sbtopts (Linux/macOS)
%USERPROFILE%\.sbt\sbtopts (Windows)

2. Edit the sbtopts File:

- Open the sbtopts file in a text editor. You can add options for the JVM here.

3. Specify the Java Version Using -jvm-version:

- Use the -jvm-version option followed by the desired Java version. For example, to use Java 11, you would add the following line to your sbtopts file:

-jvm-version 11

- If you want to use a specific JDK installation path instead of relying on the JAVA_HOME environment variable, you can use -java-home option:

-java-home /path/to/your/jdk

4. Example sbtopts file (using Java 11 with JDK path):

-jvm-version 11
-java-home /Library/Java/JavaVirtualMachines/jdk-11.0.15.jdk/Contents/Home (macOS example)
-Xmx4G

- In this example, the -Xmx4G option sets the maximum heap size to 4 gigabytes, which is often beneficial for larger projects or longer builds.

5. Important Considerations:

- The -jvm-version option will try to discover the java installations available on your computer. If a suitable version is not found, the build will fail. The -java-home option is recommended for making sure sbt uses the required java version.
- You can specify other JVM options in the sbtopts file, such as memory settings (e.g., -Xmx for maximum heap size).
- If you use different Java versions for different projects, you might need to configure the sbtopts file specifically for those projects. You may consider using an environment variable SBT_OPTS.
- If your sbt project resides within a directory, you can create a .sbtopts file in the root directory of your sbt project. sbt will search for the sbtopts files up the directory hierarchy when launching the sbt console.

6. Verify the Java Version Used by SBT:

- To verify the Java version in use, you can open an SBT console and run the java -version command, which will display the version of java being used for that SBT session.

By configuring the sbtopts file as described above, you can reliably set the Java version for your SBT builds.

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