3 Project — Spring Boot

# First, install GraalVM JDK 17+ and native-image tool # Then run: mvn native:compile -Pnative Your Spring Boot 3 application will start in and use ~30% less memory — ideal for serverless and Kubernetes. ⚠️ Note: Some dynamic features (reflection, proxies) require hints or @NativeHint . 6. Typical Project Structure src/ ├── main/ │ ├── java/com/example/boot3/ │ │ ├── Boot3Application.java // @SpringBootApplication │ │ ├── controller/ │ │ ├── service/ │ │ ├── repository/ │ │ ├── model/ │ │ ├── client/ // HTTP interfaces │ │ └── config/ // @Configuration classes │ └── resources/ │ ├── application.yml │ ├── application-dev.yml │ └── db/migration/ // Flyway/Liquibase scripts └── test/ 7. Sample application.yml spring: datasource: url: jdbc:postgresql://localhost:5432/boot3db username: appuser password: $DB_PASSWORD:secret jpa: hibernate: ddl-auto: validate open-in-view: false threads: virtual: enabled: true # Enable virtual threads (Java 21+) server: error: include-message: always compression: enabled: true

@RestController public class OrderController private final ObservationRegistry observationRegistry; @GetMapping("/order/id") public Order getOrder(@PathVariable Long id) return Observation.createNotStarted("order.fetch", observationRegistry) .observe(() -> fetchOrder(id)); spring boot 3 project

<build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> A. Jakarta Namespace (Replaces javax) // Spring Boot 2 import javax.persistence.Entity; import javax.persistence.Id; // Spring Boot 3 import jakarta.persistence.Entity; import jakarta.persistence.Id; B. HTTP Interfaces – Declarative REST Clients Spring Boot 3 allows you to define REST clients as interfaces: # First, install GraalVM JDK 17+ and native-image