Updated November 2026

Migrating to Spring Boot 4 with AI Coding Agents

Class Duration

7-14 hours of live training delivered over 1-2 days, depending on the depth of coverage and the number of services being migrated.

Student Prerequisites

Working experience building and maintaining Spring Boot 3.x applications
Comfort with Maven or Gradle builds and dependency management
Familiarity with JUnit and Spring's testing support
Experience with an AI coding assistant is helpful but not required

Target Audience

Java engineers, tech leads, and platform teams who own Spring Boot 3.x services and must move them to Spring Boot 4. It covers single services and upgrades across many services and internal starters. Engineers new to Spring Boot should start with Java with Spring Boot: Secure REST APIs.

Description

This course gives teams a repeatable path from Spring Boot 3.x to Spring Boot 4 and Spring Framework 7. Open-source support for Spring Boot 3.5 ended on June 30, 2026, and 3.5.16 was the last open-source release. Spring Boot 4 moves to Jakarta EE 11 and Jackson 3, adopts JSpecify, splits auto-configuration into modular starters, and drops Undertow. Students build a test safety net, upgrade dependencies in order, and automate the mechanical changes with OpenRewrite. AI coding agents then work through the remaining compile errors and test failures, with the build and tests checking every change.

Learning Outcomes

Assess the migration effort for a Spring Boot 3.x service.
Build a safety net of characterization and serialization tests.
Sequence the upgrade from the latest 3.5.x to Spring Boot 4.
Run and customize OpenRewrite recipes for Spring Boot 4.
Move to the new modular starters.
Migrate JSON handling to Jackson 3 without breaking clients.
Adopt JSpecify null-safety annotations.
Update tests for @MockitoBean, MockMvc, and RestTestClient.
Verify agent-made changes with builds, tests, and contract checks.
Plan upgrades across many services and internal starters.

Training Materials

All students receive comprehensive courseware covering all topics in the course. Courseware is distributed via GitHub in the form of documentation and extensive code samples.

Software Requirements

Students will need a free, personal GitHub account to access the courseware. Students will need permission to install a JDK (Java 25 LTS recommended; Spring Boot 4 requires Java 17 or later), Maven or Gradle, Docker or another container runtime for Testcontainers, and IntelliJ IDEA or Visual Studio Code with Java extensions. Examples migrate from Spring Boot 3.5 to the current Spring Boot 4.x release. Students will also need access to an AI coding agent such as Claude Code, GitHub Copilot, or Cursor. If students are unable to configure a local environment, a cloud-based environment can be provided.

Training Topics

Why Migrate, and When

End of open-source support for Spring Boot 3.5
Commercial support vs. upgrading
Support windows for 4.x releases
Estimating migration effort
Test coverage and third-party dependencies

What Changed in Spring Boot 4 and Spring Framework 7

Java 17 baseline, Java 25 recommended
Kotlin 2.2 baseline
Jakarta EE 11 and Servlet 6.1
JPA 3.2 and Bean Validation 3.1
Undertow removed
Choosing between Tomcat and Jetty
Modular auto-configuration and starters
JSpecify replacing Spring's nullness annotations
Removed 3.x deprecated APIs
Built-in API versioning
Resilience annotations such as @Retryable
HTTP service client groups
Moving from RestTemplate to RestClient

Upgrade Order

Latest Spring Boot 3.5.x first
Clearing deprecation warnings
JDK and build plugin upgrades
Spring Security and Spring Data together
The Spring Cloud release train
Unmanaged dependencies
springdoc-openapi and Hibernate extensions
Renamed properties with spring-boot-properties-migrator

Modular Starters

The new starter naming scheme
Matching test starters
spring-boot-starter-webmvc
Security OAuth2 starter renames
Classic starters as a stepping stone
Flyway and Liquibase starters
Spring Batch starter changes

Jackson 3

New tools.jackson group IDs and packages
Unchanged jackson-annotations
JsonMapper and JsonMapperBuilderCustomizer
@JacksonComponent and @JacksonMixin
Properties under spring.jackson.json
spring.jackson.use-jackson2-defaults
The deprecated Jackson 2 fallback module

Data, Security, and Web Changes

Hibernate 7 and JPA 3.2
Spring Security 7 lambda-only DSL
Removed Spring Security APIs
RestClient and WebClient starters
Message converter customization
MongoDB and session property moves
Persistence property moves

Testing Before, During, and After

Characterization tests for critical endpoints
Contract tests and JSON snapshots
Testcontainers and @ServiceConnection
@MockBean to @MockitoBean
@SpyBean to @MockitoSpyBean
@AutoConfigureMockMvc for MockMvc
@AutoConfigureTestRestTemplate
RestTestClient
Replacing JUnit 4 SpringRunner
Startup and health-probe checks
Performance and native-image checks

Automating with OpenRewrite

Lossless semantic trees and recipes
The UpgradeSpringBoot_4_0 recipe
The MigrateToModularStarters recipe
Maven and Gradle plugins
Dry runs and diff review
Committing in stages
Declarative recipes for internal frameworks
What recipes cannot do

Migrating with AI Coding Agents

Compile-error triage
Removed-API replacements
Test repairs and diff explanations
Recipes first, agents second
A written migration spec
Migration guide and release notes as context
Build, test, and run after each change
Small commits on a migration branch
No deleted tests or suppressed warnings
Behavior shifts in JSON and null handling
Security rule changes

Portfolio Migrations

Inventorying services and versions
Parent POMs, BOMs, and internal starters
Recipes and agents across repositories
Tracking progress and stragglers
Canary releases and rollback