Version 06.01.01 · JDK 21+ · EUPL 1.2

Dependency Injection
that decides at call time.

DDI lets plain Java logic pick the implementation on every @Inject. Pricing tiers, quotas, roles, feature flags, multi-tenancy, mocks — without a single if in your domain code.

Get Started → See the resolver View on GitHub

Resolver — runs on every @Inject

@ResponsibleFor(ReportGenerator.class)
class ReportPolicy implements ClassResolver<ReportGenerator> {
  public Class<? extends ReportGenerator> resolve(Class<ReportGenerator> i) {
    var user = SecurityContext.current();           // e.g. jSentinel
    if (user.quotaExceeded())   return ThrottledReport.class;
    return switch (user.plan()) {
      case FREE       -> BasicReport.class;
      case PRO        -> FullReport.class;
      case ENTERPRISE -> FullReportWithSLA.class;
    };
  }
}

Why DDI

A nano library with one big idea: cross-cutting decisions belong in the resolver, not in your services.

Dynamic Resolution

ClassResolver runs on every @Inject — pick the impl with whatever Java logic you need.

Nano Footprint

Five public classes in the core. No XML, no annotation processor, no container.

Mock by Design

Tests use the same resolver mechanism — no Mockito, no PowerMock, no surprises.

Mutation-proven

Over 90% PIT mutation coverage. The library tests itself the way you should test yours.

When is the implementation chosen?

Classic DI containers bind at startup. CDI matches qualifiers statically. DDI hands the decision to your own code — every single time the field is injected.

How ClassResolver works →

Framework	Bound when?	Runtime change?
Spring	Container refresh	Profile flip + restart
Guice	Injector build	New injector
CDI / Weld	Qualifier match (static)	Hard-coded in annotation
DDI	Per `@Inject` lookup	Your own Java logic

Drop it into your build

✓ JDK 21+, runs in any plain-Java process — CLI, Lambda, Vaadin, JavaFX.
✓ Five public classes in the core. No container, no XML.
✓ Reflections-based classpath scan; bootstrap is one method call.
✓ Licensed under EUPL 1.2 — friendly to commercial use.

Maven coordinates

<dependency>
  <groupId>com.svenruppert</groupId>
  <artifactId>ddi</artifactId>
  <version>06.01.01</version>
</dependency>

Bootstrap

DI.activatePackages("com.example");
MyService svc = DI.activateDI(MyService.class);

Consulting

Plan-aware architecture, done right

Workshops, architecture reviews and pair-programming for teams introducing per-user / per-plan logic into Java backends — without rewriting their domain layer.

Learn more →

Sponsoring

Support continued maintenance

DDI is open source. Sponsoring keeps releases predictable and the roadmap public.

Become a sponsor →

Dependency Injectionthat decides at call time.