03
Demo 03 — AppCDS Startup Acceleration
Spring Boot 4.0.5 / Java 21
⏱ ~8 min
Run this demo
View source on GitHub ↗
cd demo-03-appcds
chmod +x demo.sh
./demo.shAppCDS caches parsed + verified bytecode from the classpath. Spring Boot gets ~35-55% improvement — significantly more than Quarkus (~5%) because Spring Boot loads thousands of classes at startup that AppCDS can accelerate.
Why Spring Boot benefits so much
Spring Boot’s fat JAR classpath typically contains 8,000-12,000 classes loaded at startup for auto-configuration, component scanning, and dependency injection. AppCDS caches all of these as pre-parsed, pre-verified bytecode — eliminating the most expensive part of Spring Boot startup.
Quarkus moves most of this work to build time, which is why AppCDS only gives ~5% there. For Spring Boot, AppCDS addresses the largest remaining startup bottleneck.
Three-stage Containerfile
| Stage | Purpose |
|---|---|
| builder | mvn package to create the fat JAR |
| trainer | Run the app once with -XX:ArchiveClassesAtExit to dump the class list |
| runtime | Run with -XX:SharedArchiveFile to load the cached classes |
# Stage 2: Training run — creates the AppCDS archive
FROM ubi9/openjdk-21-runtime AS trainer
COPY --from=builder /app/target/*.jar app.jar
RUN java -XX:ArchiveClassesAtExit=app-cds.jsa \
-Dspring.context.exit=onRefresh \
-jar app.jar || true
# Stage 3: Runtime — uses the pre-built archive
FROM ubi9/openjdk-21-runtime
COPY --from=trainer /app/app-cds.jsa app-cds.jsa
COPY --from=builder /app/target/*.jar app.jar
ENTRYPOINT ["java", "-XX:SharedArchiveFile=app-cds.jsa", "-jar", "app.jar"]
Honest benchmark
| Configuration | Startup time | Delta |
|---|---|---|
| Spring Boot baseline | ~4-8s | — |
| Spring Boot + AppCDS | ~2.4s | -35-55% |