Mastering Java Modules: A Beginner's Guide to JPMS
The Java Platform Module System (JPMS) was introduced in Java 9 as part of Project Jigsaw. JPMS allows developers to define explicit dependencies between modules and control their accessibility.
Project Jigsaw was introduced to modularize the JDK and improve scalability, security, and maintainability.
Benefits of the Java Platform Module System (JPMS)
🔹 Strong Encapsulation
- Unlike traditional JAR files, JPMS allows developers to define which parts of a module are accessible to other modules.
🔹 Improved Maintainability
- JPMS forces explicit dependencies, reducing accidental dependency leaks.
🔹 Better Performance (Faster Startup & Smaller Footprint)
- The JVM can avoid loading unnecessary classes, leading to faster application startup and reduced memory usage.
- JPMS allows developers to customize the runtime using
jlink.
🔹 Stronger Security
- JPMS prevents reflection-based access to non-exported packages, reducing security risks.
Trade-offs of JPMS
🔹 Increased Complexity
- Developers need to learn a new way of structuring applications.
- Module declarations (
module-info.java) add extra overhead.
🔹 Compatibility Issues with Legacy Libraries
- Many third-party libraries do not support JPMS, requiring automatic modules or workarounds.
📊 Comparison of JPMS Benefits vs. Trade-offs
| Aspect | Benefits | Trade-offs |
|---|
| Encapsulation | Strong encapsulation through explicit exports of packages. Helps reduce unintended API exposure. | Requires careful management of module visibility, adding complexity. |
| Maintainability | Improved maintainability through modularization and clear dependency declarations. | Adds overhead in refactoring and modularizing large legacy systems. |
| Performance | Faster startup, reduced memory usage, and potential for creating lean runtime images with jlink. | May not show immediate performance gains unless properly structured. |
| Security | Prevents unauthorized access to internal packages, especially via reflection. | Some frameworks may require special handling due to restricted access. |
| Configuration | Resolves classpath issues, providing explicit dependency management. | Can be difficult to integrate with legacy applications or third-party libraries. |
| Legacy Compatibility | Works well in new applications designed with modules from the start. | Compatibility issues with third-party libraries and older applications. |
📝 Conclusion
JPMS is a powerful system for structuring Java applications but comes with trade-offs in complexity and compatibility. While it improves security, maintainability, and performance, integrating it into legacy applications may require additional effort.
