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Build-Time Dependency Injection Explained

· One min read
Vinit Shinde
Vinit Shinde
Creator of Korus Framework

Most Java frameworks use runtime DI, where objects are created and wired when the application starts.
This works — but it's slow, unpredictable, and memory-heavy.

Korus takes a different approach:

All dependency injection is generated at compile time.

No reflection.
No proxies.
No classpath scanning.

Why Build-Time DI?​

Build-time DI solves three major problems:

Slow Startup​

Runtime DI frameworks scan the classpath and perform reflection when the app boots.

Korus eliminates this entirely.

Hidden Runtime Errors​

Many DI issues (circular dependencies, missing beans) are discovered only when you run the app.

Korus validates the entire DI graph at compile time.

Large Memory Footprint​

Reflection metadata, runtime registries, proxies — all reduce performance.

Korus generates pure Java code instead.

How Korus Generates the DI Graph​

During compilation, the Korus processor:

  1. Scans your source code
  2. Builds an internal DI model
  3. Sorts beans with a topological algorithm
  4. Generates:
    • Constructor injection code
    • Method injection code
    • Singleton registries
    • Route metadata
    • A full KorusMain bootstrap class

Everything is resolved before your application even runs.

Example Generated Code (Simplified)​

public final class UserService$$KorusBean {
    private final UserRepository repo;

    public UserService$$KorusBean(UserRepository repo) {
        this.repo = repo;
    }

    public UserService get() {
        return new UserService(repo);
    }
}