This project is a best-in-class reference architecture for running modern Spring Boot applications on Google App Engine (Standard) while leveraging high-performance Java 25 features and GAE Legacy APIs.

Transitioning legacy GAE apps to modern Java runtimes often feels like a trade-off. This sample proves you can have it all: Jakarta EE 11 compatibility, Virtual Threads for scale, and seamless Google Cloud integration without the boilerplate of legacy XML configurations.

• Virtual Threads (Loom): Pre-configured to handle massive concurrency for blocking GAE API calls (Datastore, URLFetch) without thread pool exhaustion.
• Spring Cache (@Cacheable): Seamlessly integrated with GAE Memcache via JSR-107.
• Warmup Handling: Implements /_ah/warmup to prime the Spring context and caches.

• GAE + Spring Security 7.x: Bridges Google Accounts directly to Spring roles.
• Automatic Role Mapping: Google Project Admins are automatically mapped to ROLE_ADMIN.
• Annotation-Driven: Use standard @PreAuthorize instead of legacy XML security constraints.

• Custom Health Indicators: Deep monitoring of Datastore and Memcache via /actuator/health.
• GAE Metrics in Actuator: Real-time GAE statistics exposed via Micrometer.
• Unified Logging: GAE system logs (JUL) are bridged into SLF4J/Logback.
• OpenAPI 3 / Swagger: Auto-generated documentation and interactive UI at /swagger-ui.html.

mvn clean package appengine:run

Once started, visit http://localhost:8080/ to see the home page. Try the following URLs:

• Home (JSP): http://localhost:8080/
• Aliens (JSON): http://localhost:8080/aliens
• Admin Info: http://localhost:8080/admin (Requires ROLE_ADMIN / GAE Admin)
• GAE API Status: http://localhost:8080/api/gae/status
• Swagger UI: http://localhost:8080/swagger-ui.html

• Health: http://localhost:8080/actuator/health
• Metrics: http://localhost:8080/actuator/metrics
• Environment: http://localhost:8080/actuator/env
• Beans: http://localhost:8080/actuator/beans
• Thread Dump: http://localhost:8080/actuator/threaddump
• Loggers: http://localhost:8080/actuator/loggers

No more static factories. Inject GAE services as standard Spring Beans:

@RestController
public class MyController {
    private final DatastoreService datastore; // Auto-wired from AppEngineConfig
}

Leverage standard Spring Security annotations to protect your GAE application:

@PostMapping("/admin-only")
@PreAuthorize("hasRole('ADMIN')")
public String adminAction() {
    return "Only Google App Engine Admins can see this!";
}

mvn appengine:deploy

• Runtime: App Engine Standard (Java 25)
• Framework: Spring Boot 4.0.3 (Jakarta EE 11)
• Caching: JSR-107 / GAE Memcache
• Web Server: Jetty 12.1
• Testing: JUnit 5 + MockMvc + GAE LocalServiceTestHelper