Maven 4.0.0: A Major Leap Forward with Maven Shell (mvnsh)

One of my LinkedIn connections, Saeed Zarinfam , recently shared an exciting update about Maven 4.0.0. He mentioned:

Maven 4 will introduce a new shell (mvnsh) that reduces build times by keeping a single Maven process running during the session.
        

Intrigued by this, I decided to dive deeper into this new feature and conduct some R&D on Maven 4.0.0. My research revealed that this release brings not only the Maven Shell (mvnsh) but also a host of other enhancements that modernize Maven and significantly improve developer productivity.

In this article, I’ll share what I’ve discovered about Maven 4.0.0, with a particular focus on the Maven Shell and its transformative potential for Java development workflows.

What’s New in Maven 4.0.0?

Maven 4.0.0 is the first major release in over a decade, addressing long-standing issues while introducing new features to align with the needs of modern software development. Let’s explore the key highlights:

1. Updated POM Model

The Project Object Model (POM) has been enhanced for better readability and functionality:

• Improved Structure: The new XML schema makes POM files easier to understand and manage.
• Advanced Dependency Management: Developers now have more granular control over dependencies, including optional and transitive dependencies.

2. Enhanced Build Performance

Build performance has been improved through:

• Incremental Builds: Maven now rebuilds only the parts of the project that have changed, reducing unnecessary processing.
• Improved Parallelization: Build tasks and plug-ins can execute more efficiently in parallel, speeding up multi-module projects.

3. Support for Modern Java Versions

Maven 4.0.0 ensures full compatibility with the latest Java versions, including:

• Java modules (introduced in Java 9).
• New language features like records and sealed classes.
• Comprehensive support for JDK 17, the current Long-Term Support (LTS) version.

4. Smarter Dependency Resolution

The dependency resolution process has been refined:

• Better Conflict Resolution: Maven uses an improved algorithm to resolve conflicts between transitive dependencies.
• Improved Scope Management: Dependency scopes are more effectively managed, leading to reproducible builds.

5. The Maven Wrapper

Maven 4.0.0 introduces the Maven Wrapper, a long-awaited feature. Similar to Gradle’s wrapper, it allows projects to include a script that downloads and runs a specific version of Maven, ensuring consistency across team environments.

6. Modernized Plug-In Ecosystem

Plug-ins have been updated to leverage newer APIs, improving compatibility and performance. The plug-in development process has also been simplified, encouraging more developers to create custom plug-ins.

7. Improved Logging and Errors

Logs and error messages are now more structured and developer-friendly, making it easier to debug issues and understand build failures.

Maven Shell (mvnsh): A Game-Changing Feature

The Maven Shell (mvnsh) is one of the most revolutionary features in Maven 4.0.0. As my LinkedIn connection Saeed Zarinfam mentioned, it introduces a persistent session that reduces build times by keeping a single Maven process running during a session.

What is Maven Shell?

Maven Shell is an interactive command-line interface (CLI) that eliminates the overhead of starting a new JVM process for every Maven command. Instead, it keeps a persistent JVM process active, allowing developers to execute commands faster and maintain the state of their project across multiple tasks.

Key Features of Maven Shell

1. Interactive Command Execution

With Maven Shell, developers can execute commands interactively without restarting Maven for each task. For example:

$ mvnsh
maven> clean
maven> compile
maven> package
        

This reduces the repetitive overhead of starting a new Maven process for every command, streamlining the build workflow.

2. Faster Build Performance

Maven Shell keeps the JVM alive throughout the session, avoiding the repeated initialization of the JVM, project configuration, and dependency resolution. This results in significant performance improvements, especially for large, multi-module projects.

3. Auto-Completion and Suggestions

Maven Shell includes auto-completion and context-aware suggestions, making it easier to discover and execute commands. For example:

• Typing cl and pressing Tab will auto-complete the command to clean.
• The shell suggests available goals, profiles, and plug-ins as you type.

4. Stateful Environment

Maven Shell maintains the state of your project across commands:

• Active profiles persist throughout the session.
• Previously executed goals and configurations can be reused without reloading the project.

This stateful behavior is especially useful for iterative tasks, as it reduces redundancy and simplifies workflows.

5. Plug-In Exploration

The Maven Shell allows developers to explore and invoke Maven plug-ins interactively. For example, to view detailed information about the maven-compiler-plugin, you can run:

maven> help:describe -Dplugin=compiler
        

This displays the plug-in’s goals, parameters, and default values, making it easier to understand and use.

6. Custom Aliases

Maven Shell supports custom aliases for frequently used sequences of commands. For example:

maven> alias add build-all="clean install site"
        

You can now execute build-all instead of typing the full command chain every time.

7. Built-In Help

Maven Shell includes built-in help commands, making it more accessible to beginners. Use commands like help or help:describe to access documentation directly within the shell.

How to Use Maven Shell

Installation

Maven Shell is included with Maven 4.0.0 or later. To verify your Maven version, run:

mvn --version
        

Starting Maven Shell

To start the Maven Shell, simply run:

mvnsh
        

This launches an interactive session where you can begin entering commands.

Exiting Maven Shell

To exit the Maven Shell, type:

maven> exit
        

Or press Ctrl + D.

Benefits of Maven Shell

1. Improved Productivity: Faster commands and reduced overhead streamline workflows.
2. Ease of Use: Auto-completion and built-in help make Maven more accessible.
3. Iterative Development: Stateful sessions allow developers to iterate without starting a new process for each task.
4. Exploration and Debugging: Interactive exploration of goals and plug-ins simplifies debugging and experimentation.

Migration to Maven 4.0.0

Upgrading to Maven 4.0.0 is straightforward, as it maintains strong backward compatibility. To make the most of this release:

1. Test your builds to ensure compatibility with existing plug-ins and dependencies.
2. Update custom plug-ins to leverage the latest APIs.
3. Explore new features like the Maven Wrapper and Maven Shell to improve your workflows.

Conclusion

Maven 4.0.0 is a transformative release that modernizes build automation while staying true to Maven’s core principles. The introduction of the Maven Shell (mvnsh) is particularly noteworthy, offering a faster, more interactive way to work with Maven builds. By keeping a persistent JVM process running during the session, it reduces build times and enhances productivity.

Thanks to Saeed Zarinfam for highlighting this feature—it’s clear that Maven 4.0.0 is a must-have for developers looking to streamline their workflows. If you haven’t already, it’s time to upgrade and experience the future of build automation!