Upgrade Spring Boot from 2.1.3 to 3.4.0 and Java from 8 to 21

[Copilot]

This PR successfully upgrades the Spring Petclinic server module from Spring Boot 2.1.3 to 3.4.0 and updates the Java target version from 8 to 21, addressing the requirements outlined in the upgrade plan.

🚀 Major Changes

Core Framework Upgrades

• Spring Boot: 2.1.3.RELEASE → 3.4.0
• Java Target Version: Java 8 → Java 21
• Maven Wrapper: 3.3.3 → 3.9.9

Automated Migration with OpenRewrite

Used OpenRewrite Maven plugin to automatically handle the complex migration from Spring Boot 2.x to 3.x:

• Jakarta EE Migration: All javax.* packages migrated to jakarta.* (JPA, Persistence, etc.)
• JUnit Framework: Upgraded from JUnit 4 to JUnit 5 with proper annotations and extensions
• Spring Data: Updated repository method names (getOne() → getReferenceById())
• Mockito Integration: Updated to Spring Boot 3.x compatible versions

Configuration Updates

• Added Java 21 compiler properties to parent POM
• Fixed Maven plugin configurations for Spring Boot 3.x compatibility
• Updated git-commit-id-plugin to version 4.9.10
• Resolved deprecated Spring Boot plugin parameters

🧪 Testing Results

All 118 tests are now passing ✅

The test suite validates:

• JPA/Hibernate operations with Jakarta EE persistence
• REST API endpoints with updated content-type handling
• Service layer business logic and caching
• Application context and dependency injection

Key Test Fix

Updated PetResourceTests.java to handle Spring Boot 3.x content-type behavior:

// Before: Expected "application/json;charset=UTF-8"
// After: Expects MediaType.APPLICATION_JSON
.andExpect(content().contentType(MediaType.APPLICATION_JSON))

🏃‍♂️ Runtime Validation

The application successfully starts and runs with:

• Java Runtime: OpenJDK 21.0.8
• Spring Boot Version: 3.4.0
• Web Server: Apache Tomcat 10.1.33 (Jakarta EE compatible)
• Database: HSQLDB with Hibernate 6.6.2.Final

📦 Dependency Management

All transitive dependencies have been automatically updated to Spring Boot 3.4.0 compatible versions, ensuring:

• Security patches from latest dependency versions
• Jakarta EE namespace consistency
• Java 21 compatibility across the entire dependency tree

⚠️ Client Module Status

The spring-petclinic-client module (Angular/Node.js frontend) requires separate modernization due to:

• Outdated Node.js/npm versions incompatible with modern runtimes
• Legacy frontend build pipeline requiring updates

The client dependency has been temporarily excluded from the server module to enable independent server testing and deployment.

🎯 Migration Benefits

• Performance: Java 21 runtime performance improvements
• Security: Latest Spring Boot 3.4.0 security patches
• Future-Proof: Jakarta EE standard compliance
• Maintainability: Modern dependency versions and testing frameworks
• Developer Experience: Enhanced development tools and debugging capabilities

The server module is now fully upgraded and production-ready with Spring Boot 3.4.0 and Java 21.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• bits.netbeans.org
  • Triggering command: /usr/lib/jvm/temurin-21-jdk-amd64/bin/java -classpath /home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs/.mvn/wrapper/maven-wrapper.jar -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs org.apache.maven.wrapper.MavenWrapperMain rewrite:run -Dmaven.test.skip=true (dns block)
• http://registry.npmjs.org:80/npm/-/npm-6.14.12.tgz
  • Triggering command: REDACTED, pid is -1 (http block)
• maven.java.net
  • Triggering command: /usr/lib/jvm/temurin-21-jdk-amd64/bin/java -classpath /home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs/.mvn/wrapper/maven-wrapper.jar -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs org.apache.maven.wrapper.MavenWrapperMain rewrite:run -Dmaven.test.skip=true (dns block)
• repository.apache.org
  • Triggering command: /usr/lib/jvm/temurin-21-jdk-amd64/bin/java -classpath /home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs/.mvn/wrapper/maven-wrapper.jar -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/spring-petclinic-angularjs/spring-petclinic-angularjs org.apache.maven.wrapper.MavenWrapperMain rewrite:run -Dmaven.test.skip=true (dns block)
• repository.ow2.org

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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