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# Challenge 02 — Modernize the Java Application

## Introduction

The **PhotoAlbum** application was built with Spring Boot 2.7.18 on Java 8, backed by an Oracle Database that stores photos as BLOBs. This technology stack presents several modernization challenges:

- **Spring Boot 2.x** reached end-of-life in November 2023. Spring Boot 3.x requires Java 17+ and introduces breaking namespace changes (`javax.*` → `jakarta.*`).
- **Java 8** is several major versions behind the current LTS release (Java 21), missing significant performance improvements and language features.
- **Oracle Database** is an on-premises, proprietary dependency. Replacing it with **Azure Database for PostgreSQL** aligns the application with cloud-native, open-source infrastructure.
- **BLOB storage in the database** is expensive and doesn't scale well. Migrating photo storage to **Azure Blob Storage** decouples data persistence from the database and improves performance.

In this challenge you will use the GitHub Copilot Modernization tools to create and execute a migration plan that addresses all of these concerns.

> **Note:** This challenge can be worked on in parallel with the .NET track by different members of your team.

## Description

Modernize the PhotoAlbum Java application from its current state to:

- **Spring Boot 3.x** (latest stable release)
- **Java 21**
- **Azure Database for PostgreSQL** as the relational database (replacing Oracle)
- **Azure Blob Storage** for photo file storage (replacing in-database BLOBs)

Your approach should include:

- Use the GitHub Copilot Modernization tool to generate a migration plan with a goal that captures all the migration objectives above
- Review the generated migration plan before executing it
- Execute the migration plan using the appropriate tool command
- Use GitHub Copilot Chat to resolve any compilation errors or test failures the automated migration cannot fix
- Update the `Dockerfile` to build on a Java 21 base image
- Update `application.properties` (or `application.yml`) with the new datasource and Azure Blob Storage configuration

> **Note:** Do **not** modify `docker-compose.yml` — the Oracle container must remain intact for the data migration in Challenge 04. PostgreSQL runs on Azure (provisioned in Challenge 03); there is no need for a local PostgreSQL container.

## Success Criteria

To complete this challenge successfully, demonstrate:

1. The application builds successfully with no compilation errors
2. The application configuration (`application.properties` / `application.yml`) targets Azure Database for PostgreSQL and Azure Blob Storage
3. Photos can be uploaded and retrieved successfully in the running application (test against Azure after Challenge 03 deployment, or locally with an H2 in-memory database if needed)
4. Running a fresh assessment on the updated codebase reports no remaining **mandatory blockers** for the Java 8 → Java 21 / Spring Boot 2 → 3 migration
5. The `pom.xml` reflects Spring Boot 3.x and Java 21 as the compile target
6. **Explain to your coach** — why is the `javax.*` → `jakarta.*` namespace change one of the most impactful breaking changes in the Spring Boot 2 → 3 migration?
7. **Explain to your coach** — why is storing photos as BLOBs inside a relational database a cloud-native anti-pattern? What does Azure Blob Storage solve that the database approach cannot?

## Learning Resources

- [Spring Boot 3.0 Migration Guide](https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.0-Migration-Guide)
- [Spring Boot 3.2 Migration Guide](https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.2-Migration-Guide)
- [Java 21 new features overview](https://openjdk.org/projects/jdk/21/)
- [Spring Data JPA with PostgreSQL](https://spring.io/guides/gs/accessing-data-jpa/)
- [Azure SDK for Java – Blob Storage](https://learn.microsoft.com/azure/storage/blobs/storage-quickstart-blobs-java)
- [Modernization CLI — plan commands](https://learn.microsoft.com/azure/developer/github-copilot-app-modernization/modernization-agent/cli-commands)

## Tips

- The namespace change from `javax.persistence.*` to `jakarta.persistence.*` is one of the most common sources of compilation failures after a Spring Boot 2→3 migration.
- When migrating from Oracle to PostgreSQL, pay attention to SQL dialect differences, especially around sequences, date/time types, and BLOB/CLOB handling. The application will connect to Azure Database for PostgreSQL after deployment in Challenge 03.
- Keep the Oracle `docker-compose.yml` untouched — you will need the Oracle container running in Challenge 04 to migrate production data.