How do you run multiple JVMs on the same PC?

Fellow developers, a common Java challenge involves managing multiple projects requiring different JVM versions. This often leads to frustrating errors like:

<code>Required by:
         project : > org.springframework.boot:org.springframework.boot.gradle.plugin:3.3.2
      > Dependency requires at least JVM runtime version 17. This build uses a Java 11 JVM.</code>

This post explores solutions for running applications needing Java 11 and Java 17 concurrently.

I've encountered this issue repeatedly while juggling projects with varying JVM requirements. Manually switching JVM versions is tedious and error-prone. The goal is to automate the process.

Running Multiple JVMs:

It's perfectly feasible to run multiple JVMs on a single machine. Each Java application launches its own JVM instance, operating independently. This isolation prevents conflicts between applications.

However, sufficient system resources (CPU and memory) are crucial to avoid performance bottlenecks when running multiple JVMs simultaneously.

Managing Multiple Java Versions:

Several strategies streamline the management of multiple Java installations:

• Environment Variables: Setting the JAVA_HOME environment variable directs the system to the correct Java installation. The PATH variable needs updating to include the Java executable. For Java 11, this might look like:

export JAVA_HOME=$(/usr/libexec/java_home -v 11)
export PATH=$JAVA_HOME/bin:$PATH

• Command-Line Arguments: Specify the Java executable's full path when launching an application:

/path/to/java11/bin/java -jar your-application.jar

Automating JVM Selection:

The ideal solution automates JVM selection based on project requirements. Several approaches can achieve this:

• Build Tools (Gradle, Maven): Configure your build tool (e.g., Gradle or Maven) to automatically select the appropriate Java version based on project settings in your build.gradle or pom.xml file. This is generally the preferred and most robust method.

• Shell Scripts/Batch Files: Create scripts that detect the project's required JVM version and launch the application using the correct Java executable. This provides a degree of automation but requires more manual configuration.

• Project-Specific Environment Variables: Create distinct environment variables for each project, specifying the Java version. Your application can then read these environment variables to determine which JVM to use.

I'm eager to hear your suggestions and best practices for automating JVM selection in the comments below. Let's share our knowledge and make Java development smoother!

References:

• Stack Overflow
• Code Ranch

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