Pass Spark job server JVM args

[aIbrahiim]

Fixes: #30602
Successful run: https://github.com/apache/beam/actions/runs/28941534332

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[gemini-code-assist]

Summary of Changes

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This pull request introduces the ability to pass custom JVM arguments to the Spark job server. This change is primarily aimed at resolving compatibility issues with Java 17 and newer, where specific module access flags are required. The implementation includes logic to automatically detect the Java version and apply the necessary 'add-opens' flags, while also updating the supporting shell scripts to handle these arguments during the job server lifecycle.

Highlights

• JVM Argument Support: Added support for passing custom JVM arguments to the Spark job server, enabling necessary flags for newer Java versions.
• Java 17 Compatibility: Implemented automatic detection of Java 17+ to inject required '--add-opens' flags, ensuring compatibility with modern Java environments.
• Script Updates: Updated the 'run_job_server.sh' script to accept and apply the new '--jvm_args' parameter during server startup.

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[gemini-code-assist]

Code Review

This pull request adds support for passing JVM arguments (such as --add-opens flags for Java 17+) to the Spark Job Server. It updates the Gradle setup task to dynamically determine the Java version and pass these arguments, and modifies run_job_server.sh to accept and apply them. The review feedback highlights potential issues with unquoted $JVM_ARGS in the shell script leading to word-splitting or unbound variable errors, and a potential NumberFormatException in the Gradle build file when parsing the testJavaVersion property.

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[gemini-code-assist]

When $JVM_ARGS is unquoted, it undergoes word splitting, which is necessary here to pass multiple JVM arguments (like --add-opens) as separate parameters to the java command. However, if $JVM_ARGS is empty or unset, this can sometimes lead to unexpected behavior depending on shell settings, or if any of the arguments contain spaces.

To ensure robustness and avoid issues with empty values, it is safer to use an array for arguments in bash, or explicitly handle the expansion. Since this script is executed via sh (which might be dash or bash depending on the system), we should be careful. If we are sure it's run with bash (the shebang of run_job_server.sh is likely #!/bin/bash), using a bash array is the most robust way to handle list of arguments with potential spaces. If it must remain a string, we should ensure JVM_ARGS is initialized to an empty string at the top of the script to prevent unbound variable errors if set -u is used.

[gemini-code-assist]

In Groovy/Gradle, using as int on a property that might be a String can throw a NumberFormatException if the property is not a valid integer. Additionally, JavaVersion.current().majorVersion is already a String, so calling .toInteger() on it is safe, but we should make sure testJavaVersion is safely parsed.

Consider using Integer.parseInt() or a safe cast with a fallback to avoid potential build failures if testJavaVersion is configured incorrectly.

  def testJavaVer = project.findProperty('testJavaVersion') ? (project.property('testJavaVersion').toString().toInteger()) : JavaVersion.current().majorVersion.toInteger()

[Abacn]

Thanks!