At runtime, find all classes in a Java application that extend a base class

java

reflection

dynamic-discovery

class-loader

byAnton Shumikhin·Jan 30, 2025

Your fastest route to identifying subclasses is via the Reflections library. This Java utility efficiently scans the classpath entities at runtime.

import org.reflections.Reflections;

public class ClassFinder {
  public static void main(String[] args) {
    Reflections reflections = new Reflections("your.package.name"); // Unleashing the magic!
    Set<Class<? extends MyBaseClass>> subTypes = reflections.getSubTypesOf(MyBaseClass.class);
    subTypes.forEach(System.out::println); // Now you see me...
  }
}

Just replace your.package.name and MyBaseClass with your details. Now sit back and let Reflections find all subclasses for you—a classic case of smart work over hard work!

Reflections: Unleashing dynamic discovery

When it comes to adding flexibility to your Java applications or reducing manual coding, dynamic class discovery is the way to go. Here's how the Reflections library helps.

Reflections: The showstopper

User-Friendliness: Just define the package and class, and let Reflections run the show.
Automatic Updates: Newly added subclasses are automatically detected—no need for manual configuration!
Lightness: Offering a less complex alternative to Java's built-in ServiceLoader.

Pitfalls of Reflections

Reflections isn't all sunshine and roses. Watch out for these potential challenges:

Performance Hits: Reflection can be resource-intensive, leading to potential performance issues.
Security Vulnerabilities: Be careful, as Reflection may expose internal APIs, creating potential security risks.
Complexity: Inadequate handling of Reflections can lead to increased complexity and debugging woes.