Upgrade to Spring Boot 4.0 and JDK 25 LTS

## Description

The project currently uses **Spring Boot 3.4.4** and **JDK 21 (LTS)**. Spring Boot 4.0.0 was [released on November 20, 2025](https://spring.io/blog/2025/11/20/spring-boot-4-0-0-available-now) with support for **JDK 25 LTS** ([released September 2025](https://adoptium.net/news/2025/09/eclipse-temurin-25-available)). This issue tracks the upgrade to the latest LTS versions of both Spring Boot and the JDK.

### Current Configuration

**Maven POM (`pom.xml`):**
```xml
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.4.4</version>
</parent>

<properties>
    <java.version>21</java.version>
    <maven.compiler.source>21</maven.compiler.source>
    <maven.compiler.target>21</maven.compiler.target>
</properties>
```

**Docker (`Dockerfile`):**
```dockerfile
FROM eclipse-temurin:21-jdk-alpine AS build
FROM eclipse-temurin:21-jre-alpine AS runtime
```

### Why Upgrade?

**Spring Boot 4.0 Key Features:**
- Native support for JDK 25 LTS
- Jakarta EE 11 baseline (upgraded from EE 10)
- Spring Framework 7.0 foundation
- Enhanced observability and metrics
- Improved performance and memory efficiency
- Migration to `org.springframework.boot.test.mock.mockito.MockBean` deprecation (replaced with standard Mockito)

**JDK 25 LTS Benefits:**
- Latest LTS with long-term support until 2032
- Performance improvements and security patches
- New language features (pattern matching enhancements, structured concurrency, etc.)
- Better garbage collection improvements
- Generational ZGC and Shenandoah enhancements

## Proposed Solution

Perform a coordinated upgrade of Spring Boot and JDK in a single migration:

1. **Update to Spring Boot 4.0.0** (or latest 4.x)
2. **Update to JDK 25 LTS**
3. **Fix breaking changes** (Jakarta EE 11, deprecated APIs)
4. **Update Docker images** to JDK 25
5. **Update CI/CD pipelines**
6. **Update documentation**
7. **Test thoroughly**

## Migration Checklist

### 1. Update Spring Boot Version

**`pom.xml`:**
```xml
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>4.0.0</version> 
</parent>

<properties>
    <java.version>25</java.version>
    <maven.compiler.source>25</maven.compiler.source>
    <maven.compiler.target>25</maven.compiler.target>
</properties>
```

### 2. Update Test Annotations

Spring Boot 4.0 deprecates `@MockBean` in favor of standard Mockito `@MockitoBean`:

**Before (Spring Boot 3.x):**
```java
import org.springframework.boot.test.mock.mockito.MockBean;

@WebMvcTest(BooksController.class)
class BooksControllerTests {
    @MockBean
    private BooksService booksServiceMock;
}
```

**After (Spring Boot 4.0):**
```java
import org.springframework.test.context.bean.override.mockito.MockitoBean;

@WebMvcTest(BooksController.class)
class BooksControllerTests {
    @MockitoBean
    private BooksService booksServiceMock;
}
```

**Files to update:**
- `BooksControllerTests.java` - Replace `@MockBean` with `@MockitoBean`
- `BooksServiceTests.java` - Use standard Mockito `@Mock` and `@InjectMocks` (no changes needed)

### 3. Update Docker Configuration

**`Dockerfile`:**
```dockerfile
FROM eclipse-temurin:25-jdk-alpine AS build
WORKDIR /workspace/app

COPY mvnw .
COPY .mvn .mvn
COPY pom.xml .
COPY src src

RUN ./mvnw package -DskipTests
RUN mkdir -p target/dependency && (cd target/dependency; jar -xf ../*.jar)

FROM eclipse-temurin:25-jre-alpine AS runtime
VOLUME /tmp
ARG DEPENDENCY=/workspace/app/target/dependency
COPY --from=build ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY --from=build ${DEPENDENCY}/META-INF /app/META-INF
COPY --from=build ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","ar.com.nanotaboada.java.samples.spring.boot.Application"]
```

### 4. Update CI/CD Pipelines

**GitHub Actions (`.github/workflows/maven.yml`):**
```yaml
- name: Set up JDK 25
  uses: actions/setup-java@v4
  with:
    java-version: '25'
    distribution: 'temurin'
```

**Azure Pipelines (`azure-pipelines.yml`):**
```yaml
- task: JavaToolInstaller@0
  inputs:
    versionSpec: '25'
    jdkArchitectureOption: 'x64'
    jdkSourceOption: 'PreInstalled'
```

### 5. Review Dependency Versions

Check and update versions for Spring Boot 4.0 compatibility:

- [ ] **Lombok** - Verify JDK 25 annotation processing works (update to 1.18.36+)
- [ ] **SpringDoc OpenAPI** - Update to version compatible with Spring Boot 4.0
- [ ] **ModelMapper** - Verify compatibility
- [ ] **JaCoCo** - Verify bytecode instrumentation works with class version 69 (JDK 25)
- [ ] **Mockito** - Should be managed by Spring Boot 4.0 (verify version supports JDK 25)

### 6. Update Documentation

**Files to update:**
- [ ] `.github/copilot-instructions.md` - Change all JDK 21 / Spring Boot 3.x references
- [ ] `README.md` - Update Prerequisites section (JDK 25, Spring Boot 4.0)
- [ ] `CONTRIBUTING.md` - Update development setup instructions
- [ ] `pom.xml` - Update `<description>` if it mentions Spring Boot 3

**Key sections:**
- Prerequisites: "JDK 25 (LTS) required"
- Stack: "Spring Boot 4.0"
- Troubleshooting: Update JAVA_HOME examples
- Build commands: Verify Maven wrapper works with JDK 25

### 7. Testing Strategy

- [ ] Run full test suite: `./mvnw verify`
- [ ] Verify all 32+ tests pass
- [ ] Check JaCoCo coverage reports generate correctly
- [ ] Test Docker build: `docker compose build`
- [ ] Test Docker run: `docker compose up`
- [ ] Verify Swagger UI: `http://localhost:9000/swagger/index.html`
- [ ] Verify Actuator: `http://localhost:9001/actuator/health`
- [ ] Run application locally: `./mvnw spring-boot:run`
- [ ] Test all CRUD endpoints + search endpoint
- [ ] Performance testing (compare before/after)

## Breaking Changes to Address

### Jakarta EE 11 Namespace Changes

Spring Boot 4.0 moves to Jakarta EE 11. Most imports should remain the same (`jakarta.*`), but verify:

- `jakarta.validation` - Bean Validation 3.1
- `jakarta.persistence` - JPA 3.2
- `jakarta.servlet` - Servlet 6.1

### Deprecated APIs

Review Spring Boot 4.0 migration guide for deprecated APIs:
- `@MockBean` → `@MockitoBean` (already noted above)
- Check for any other deprecations in controller/service layers

### Configuration Properties

Review `application.properties` for any deprecated property keys and update to new names per Spring Boot 4.0 migration guide.

## Acceptance Criteria

- [ ] All Maven builds pass with JDK 25: `./mvnw clean verify`
- [ ] All 32+ unit tests pass without errors or warnings
- [ ] Test coverage remains at 100% for controller and service layers
- [ ] Docker image builds successfully with JDK 25 base images
- [ ] Application runs without errors on Spring Boot 4.0 + JDK 25
- [ ] GitHub Actions CI pipeline passes
- [ ] Swagger UI works correctly
- [ ] Actuator endpoints respond correctly
- [ ] Documentation updated to reflect Spring Boot 4.0 and JDK 25
- [ ] No performance regressions (benchmark if needed)
- [ ] All CRUD endpoints + search endpoint function correctly

## Edge Cases & Risks

### 1. Mockito Agent Loading Warnings

**Current behavior (JDK 21):**
```
WARNING: A Java agent has been loaded dynamically
WARNING: Dynamic loading of agents will be disallowed by default in a future release
```

**Risk:** JDK 25 may enforce stricter agent loading policies
**Mitigation:** 
- Follow Spring Boot 4.0 guidance on Mockito configuration
- Consider adding Mockito agent to Maven Surefire plugin configuration
- Use `@MockitoBean` instead of `@MockBean`

### 2. CLOB Handling in H2

**Current:** Using `CAST(description AS string)` in JPQL for H2 CLOB fields
**Risk:** H2 database version bundled with Spring Boot 4.0 may behave differently
**Mitigation:**
- Test search endpoint thoroughly
- Review H2 version changes in Spring Boot 4.0 release notes
- Consider Issue #80 (H2 → SQLite migration) as future work

### 3. Third-Party Dependency Compatibility

**Risk:** Some dependencies may not yet support Spring Boot 4.0
**Mitigation:**
- Check SpringDoc OpenAPI compatibility before upgrade
- Review ModelMapper for Spring Boot 4.0 support
- Have rollback plan ready

### 4. Docker Image Size

**Risk:** JDK 25 images may be larger than JDK 21
**Mitigation:**
- Monitor image size after upgrade
- Consider using -alpine variants
- Optimize layer caching in Dockerfile

## Rollback Plan

If Spring Boot 4.0 + JDK 25 causes issues:

1. Revert `pom.xml` to Spring Boot 3.4.4 and JDK 21
2. Revert test annotations (`@MockitoBean` → `@MockBean`)
3. Revert `Dockerfile` to `eclipse-temurin:21` images
4. Revert CI/CD pipeline configurations
5. Revert documentation changes
6. Rebuild and redeploy: `./mvnw clean package`

**Rollback Trigger Conditions:**
- Test failures that cannot be resolved within reasonable time
- Critical dependency incompatibilities with no workaround
- Performance degradation > 15%
- Production issues after deployment

## Resources

- 🔗 [Spring Boot 4.0 Release Notes](https://spring.io/blog/2025/11/20/spring-boot-4-0-0-available-now)
- 🔗 [Spring Boot 4.0 Migration Guide](https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide)
- 🔗 [JDK 25 Release Notes](https://openjdk.org/projects/jdk/25/)
- 🔗 [Eclipse Temurin 25 Announcement](https://adoptium.net/news/2025/09/eclipse-temurin-25-available)
- 🔗 [Jakarta EE 11 Specification](https://jakarta.ee/specifications/)
- 🔗 [Spring Framework 7.0 What's New](https://docs.spring.io/spring-framework/reference/7.0/whatsnew.html)

## Related Issues

- #80 - Database migration (H2 → SQLite) - can be done after this upgrade
- #128 - Book search endpoint - already implemented, needs testing with Spring Boot 4.0

## Implementation Order

Since you have no rush to implement #128 (search endpoint is already complete), the recommended order is:

1. **This Issue (#232)** - Upgrade to Spring Boot 4.0 + JDK 25 **FIRST**
2. **Issue #128** - Already implemented, just needs final testing after this upgrade

This ensures the codebase is on the latest LTS stack before completing the search endpoint work.

---

**Status:** 🟢 **Ready to implement** - Both Spring Boot 4.0 and JDK 25 LTS are released and stable

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Upgrade to Spring Boot 4.0 and JDK 25 LTS #232

Description

Current Configuration

Why Upgrade?

Proposed Solution

Migration Checklist

1. Update Spring Boot Version

2. Update Test Annotations

3. Update Docker Configuration

4. Update CI/CD Pipelines

5. Review Dependency Versions

6. Update Documentation

7. Testing Strategy

Breaking Changes to Address

Jakarta EE 11 Namespace Changes

Deprecated APIs

Configuration Properties

Acceptance Criteria

Edge Cases & Risks

1. Mockito Agent Loading Warnings

2. CLOB Handling in H2

3. Third-Party Dependency Compatibility

4. Docker Image Size

Rollback Plan

Resources

Related Issues

Implementation Order

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Upgrade to Spring Boot 4.0 and JDK 25 LTS #232

Description

Description

Current Configuration

Why Upgrade?

Proposed Solution

Migration Checklist

1. Update Spring Boot Version

2. Update Test Annotations

3. Update Docker Configuration

4. Update CI/CD Pipelines

5. Review Dependency Versions

6. Update Documentation

7. Testing Strategy

Breaking Changes to Address

Jakarta EE 11 Namespace Changes

Deprecated APIs

Configuration Properties

Acceptance Criteria

Edge Cases & Risks

1. Mockito Agent Loading Warnings

2. CLOB Handling in H2

3. Third-Party Dependency Compatibility

4. Docker Image Size

Rollback Plan

Resources

Related Issues

Implementation Order

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions