Spring Boot 4.0 Migration Guide: Strategies, Challenges, and Best Practices

Upgrading to a new major version of a framework is a significant technical undertaking, and making the move to Spring Boot 4.0 is no exception. Built on Spring Framework 7 and aligned with modern Java and cloud‑native practices, it introduces architectural changes that go well beyond a routine version upgrade.

Migrating to Spring Boot 4 requires planning, testing, and setting realistic expectations. This guide walks through what Spring Boot 4 changes, why the upgrade is different from earlier transitions, and how to approach a Spring Boot migration in a way that minimizes risk.

Spring Boot 4.0 Release Date and Details 

Spring Boot 4.0 was released on November 30, 2025 and marks a major evolution of the Spring ecosystem. Spring Boot 4.0 is engineered to optimize performance, enhance cloud-native capabilities, and reduce resource consumption. It drops legacy baggage and aligns with modern enterprise standards.

Key Features and Enhancements

• Java 17+ and Spring Framework 7: Spring Boot 4 mandates Java 17 as a baseline and is built on Spring 7. This enables the use of modern JVM advancements, including virtual threads (Project Loom) for high-concurrency workloads, record classes, and pattern matching.
• Jakarta EE 11 Alignment: The enterprise Java standard continues its evolution. Version 11 finalizes the migration of all APIs from the javax.* namespace to the jakarta.* namespace.
• Enhanced Modularity: The framework now features smaller jars and lighter dependencies. This targeted dependency management enables highly efficient container images, reducing bloat by allowing you to include only necessary components.
• GraalVM Native Image Support: Ahead-of-Time (AOT) compilation allows you to build Java applications as native executables. The outcome is sub-100ms startup times and a 50-80% reduction in memory footprint. This is highly advantageous for serverless functions, microservices, and Kubernetes deployments.
• Advanced Observability: Integration with Micrometer 2 and OpenTelemetry provides a unified layer for metrics, tracing, and logging. This facilitates seamless monitoring via tools like Grafana, Prometheus, and Jaeger.
• Streamlined Cloud Integrations: Benefit from optimized OCI (Open Container Initiative) images via Spring Boot Buildpacks, native support for distro-less builds, and streamlined configurations for Kubernetes probes and config maps.

Deprecated and Removed Functionality

To maintain a streamlined architecture, several legacy features have been removed:

• Undertow Support: Ended due to maintenance lag and incompatibility with Jakarta EE 10+.
• Legacy Actuator Endpoints: Fully replaced by the Micrometer 2 observability stack.
• JMX Configuration Properties: Removed in favor of modern metrics and monitoring approaches.
• Legacy OAuth2 Auto-Configurations: Replaced by Spring Authorization Server, a dedicated and secure library for OAuth2 implementations.

Understanding the Impact of Major Spring Version Upgrades

Spring Boot 4.0 is not a drop-in upgrade. Unlike minor upgrades — which remain backward-compatible and require minimal effort — a major upgrade introduces breaking changes, drops deprecated APIs, and raises baseline dependencies.

Common Breaking Changes

• Namespace Migration: All bindings must transition from javax.* to jakarta.*.
• Dependency Cascades: Spring Boot’s Bill of Materials (BOM) strictly enforces library versions. Upgrading the Spring Boot parent cascades to Hibernate 7, Jackson 3, Tomcat, Micrometer, and Spring Security.
• Code Refactoring: Custom implementations relying on deprecated Spring APIs will fail to compile and must be rewritten.

To minimize disruption, organizations are heavily advised to upgrade to Spring Boot 3.5 and clear all deprecation warnings before attempting the leap to 4.0.

Spring Boot 4 Migration Timing Considerations

Deciding when to upgrade depends on your organization's risk tolerance, project cycles, and infrastructure readiness.

This video explains the pros and cons of immediately upgrading to the latest version and how to avoid rushed upgrades:

The Case for Early Adoption

• Longevity: Spring Boot 4’s LTS will extend until at least 2030, minimizing the need for subsequent major migrations in the near term.
• Performance Gains: Immediate access to native image builds and virtual threading translates to reduced cloud infrastructure costs.
• Security: Early adoption ensures your architecture benefits from the latest security models and OIDC compliance.

The Case for Delaying

• Ecosystem Lag: Third-party libraries and Spring Cloud modules may lack immediate compatibility with Boot 4.
• Resource Constraints: If you are actively delivering a major project on Spring Boot 3.2.x or Spring Boot 3.4.x, completing your current deliverables takes precedence. In this scenario, postponing your migration and acquiring Spring long-term support makes sense. 
• Cloud Platform Compatibility: Some managed environments (e.g., AWS Elastic Beanstalk) may require time to officially support Spring Boot 4 images.

The Risk of Inaction

Remaining on unsupported versions exposes your application to critical security vulnerabilities and technical debt, compounding the cost and complexity of future migrations.

Recent Spring CVEs

Planning Your Spring Boot 4 Migration

A successful migration requires rigorous scoping and a methodical approach. Start by evaluating your application size, dependency tree, and CI/CD readiness.

Inventorying Dependencies

Conduct an exhaustive audit of your dependencies before modifying code.

• Identify Conflicts: Map out direct and transitive dependencies to locate incompatible libraries.
• Assess Third-Party Readiness: Verify if your external drivers, security adapters, and caching mechanisms support Java 21+ and Jakarta EE 11.
• Address Vulnerabilities: Use the upgrade as an opportunity to patch outdated libraries.

Recommended Migration Path

1. Upgrade to Spring Boot 3.5 LTS: Resolve all deprecation warnings in your current environment.
2. Isolate the Work: Create a dedicated feature branch for the Boot 4 migration.
3. Update the Build File: Modify the Spring Boot version and run the build to surface compilation errors.
4. Refactor Namespaces: Systematically replace javax.* with jakarta.* and align updated APIs.
5. Execute Parallel Testing: Run comprehensive unit, integration, and end-to-end tests to validate data serialization, persistence layers, and security configurations.

Spring Boot Migration Challenges

Migration delays often occur when dependency analysis or testing is deferred too long. Identifying these risks early reduces both cost and disruption.

Typical Bottlenecks

• Configuration Property Shifts: Spring Boot 4 auto-configuration alters property handling. Expect to adjust application.properties and application.yml files to accommodate renamed or reorganized values.
• Jakarta EE 11 Refactoring: The namespace change requires deep refactoring, particularly in applications heavily reliant on direct Jakarta APIs.
• Serialization and Persistence: Migrating from Jackson 2 to 3 and Hibernate 6 to 7 frequently causes data mapping and object-relational conflicts.

Mitigating Delays

To prevent stalled migrations:

• Use an incremental approach, isolating and upgrading independent modules.
• Leverage automated testing to immediately flag regressions.
• Monitor official Spring migration guides and community repositories for documented workarounds.

How Long Does a Migration to Spring Boot 4 Take?

There is no fixed timeline for a Spring Boot 4 migration. Factors to take into consideration include: 

• Lines of Code (LOC) and Modularity: Monolithic architectures demand more concerted effort than isolated microservices.
• Test Coverage: High automated test coverage drastically reduces the timeline by pinpointing regressions instantly. Poor test coverage necessitates laborious manual testing.
• Custom Infrastructure: Highly customized security configurations or custom embedded servers will require extensive manual refactoring.

Estimating the Timeline

Instead of estimating in weeks or months, many teams find it more useful to break the work into phases — assessment, dependency alignment, code refactoring, testing, and deployment — with clear milestones at each stage:

1. Discovery Phase: Analyze dependencies, map out breaking changes, and define a rollback strategy.
2. Build Adjustment Phase: Resolve dependency conflicts and update CI/CD pipelines.
3. Refactoring Phase: The most labor-intensive step. Address deprecated APIs, update namespaces, and rewrite custom configurations.
4. Validation Phase: Execute load testing, security audits, and functional validation.
5. Deployment Phase: Utilize a phased rollout (canary deployments) to monitor stability in production safely.

Organizations can accelerate this process by utilizing automated tools like the Spring Boot Migrator (SBM) and IDE refactoring features to automate repetitive namespace and property updates.

Best Practices for a Seamless Spring Boot Upgrade

Adopt these strategic practices to ensure a predictable and secure migration process.

• Start with Lower-Risk Applications: Begin your upgrade journey with internal tools or low-traffic services. This provides a low-stakes environment for your team to identify tooling gaps, refine their checklist, and build expertise before touching mission-critical systems.
• Automate Testing Early: Do not rely on manual QA. A robust suite of unit and integration tests serves as a safety net, confirming that core business logic remains intact as underlying frameworks shift.
• Enforce Security and Compliance: Treat the upgrade as a security audit. Review your dependency tree for vulnerabilities, validate updated access controls via Spring Authorization Server, and ensure your logging mechanisms remain compliant with internal and external regulations.
• Establish Performance Baselines: Document your application's CPU and memory usage before the upgrade. Post-migration, utilize Micrometer 2 to verify that the framework's native image and AOT compilations are delivering the expected performance optimizations.
• Document and Share Knowledge: Maintain an internal knowledge base detailing the hurdles encountered and the solutions applied. Cross-team knowledge sharing prevents redundant troubleshooting and accelerates organizational momentum.

By combining meticulous planning with modern development practices, your organization can successfully navigate the Spring Boot 4.0 migration, unlocking advanced cloud-native capabilities and long-term infrastructure stability.

Final Thoughts

Spring Boot 4 is less about incremental improvement and more about establishing a modern, long‑term foundation for Java applications. Above all else, organizations should align that migration with broader platform and business priorities.

With early planning, realistic expectations, and disciplined execution, a Spring Boot 4 migration can become a controlled modernization effort rather than a disruptive upgrade.

Additional Resources

• On-Demand Webinar - Untangling the Dependency Web in Legacy Spring Applications
• Blog - Planning Your Next Spring Boot Upgrade
• Blog - Spring Boot Performance Tuning and Troubleshooting Guide
• Blog - Managing End-of-Life Spring Vulnerabilities
• Blog - Monitoring Spring Boot Applications in a Microservices World