ddd4j Extensions

Overview

Extensions are optional capabilities and must not pollute core in reverse. The current 3.0.x top-level extensions include Excel, License, Monitor, OTel, PF4J, QLExpress, QRCode, and Validation; Jackson core tooling lives in ddd4j-kit/core, and Akka currently lives mainly in ddd4j-boot.

When to Use

• Deciding which extension covers a requirement: Excel export, license control, monitoring config, trace/metrics, plugin system, rule expressions, QR codes, or extended validation.
• Adding an extension as an optional dependency with a classpath guard so a missing jar never breaks core.
• Wiring the enabled switch, default implementation, user Bean override, and explicit close for an extension.
• Sandboxing risky inputs: QLExpress function/access/time limits, PF4J plugin signature/origin/isolation.
• Checking whether an extension actually exists on the current maintenance line before promising it.
• Reviewing degradation behavior when an extension is disabled or absent.

When NOT to Use

Do not use this skill when: