Spring Boot 4.0 Migration Skill

Removed Features

Undertow

Spring Boot 4 requires Servlet 6.1, which Undertow does not yet support. Undertow starter and embedded server support have been dropped.

Pulsar Reactive

Following the decision to remove reactor support in Spring Pulsar, reactive Pulsar client management has been removed.

Embedded Launch Scripts

Support for "fully executable" jar embedded launch scripts has been removed. Use uber jars with Spring Boot's build plugins instead.

Spring Session

• Spring Session Hazelcast is now under Spring Session project
• Spring Session MongoDB is now under Spring Session project

Spock Integration

Spring Boot's Spock integration has been removed as Spock does not yet support Groovy 5.

New Modular Structure

Starter POM Naming Convention

• All modules named: spring-boot-{technology}
• All starters named: spring-boot-starter-{technology}
• Root package: org.springframework.boot.{technology}

Test Infrastructure

• All test modules named: spring-boot-test-{technology}
• All test starters named: spring-boot-starter-test-{technology}

Classic Starter POMs (Migration Aid)

For existing applications wanting quick migration, "Classic Starter POMs" provide pre-4.0 style setup:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-classic-starter</artifactId>
</dependency>

Starter POMs Available

Web

• spring-boot-starter-web-mvc (was web)
• spring-boot-starter-webflux
• spring-boot-starter-webservices

Template Engines

• spring-boot-starter-freemarker
• spring-boot-starter-groovy-templates
• spring-boot-starter-mustache
• spring-boot-starter-thymeleaf

Data Access

• spring-boot-starter-data-cassandra
• spring-boot-starter-data-couchbase
• spring-boot-starter-data-elasticsearch
• spring-boot-starter-data-jdbc
• spring-boot-starter-data-jpa
• spring-boot-starter-data-ldap
• spring-boot-starter-data-mongodb
• spring-boot-starter-data-neo4j
• spring-boot-starter-data-r2dbc
• spring-boot-starter-data-redis
• spring-boot-starter-data-rest
• spring-boot-starter-jdbc
• spring-boot-starter-jooq
• spring-boot-starter-flyway
• spring-boot-starter-liquibase

Messaging

• spring-boot-starter-artemis
• spring-boot-starter-amqp
• spring-boot-starter-kafka
• spring-boot-starter-pulsar
• spring-boot-starter-rsocket

Security

• spring-boot-starter-security
• spring-boot-starter-oauth2-authorization-server
• spring-boot-starter-oauth2-client
• spring-boot-starter-oauth2-resource-server
• spring-boot-starter-saml

Observability

• spring-boot-starter-actuator
• spring-boot-starter-micrometer
• spring-boot-starter-opentelemetry
• spring-boot-starter-zipkin

Containers

• spring-boot-starter-websocket

Other

• spring-boot-starter-cache
• spring-boot-starter-hazelcast
• spring-boot-starter-mail
• spring-boot-starter-quartz
• spring-boot-starter-validation
• spring-boot-starter-batch

Configuration Properties Migrator

Add to help migrate properties:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-properties-migrator</artifactId>
    <scope>runtime</scope>
</dependency>

Or for Gradle:

runtimeOnly("org.springframework.boot:spring-boot-properties-migrator")

Remove after migration complete.

Full Reference

For complete list of starters, module mappings, and detailed migration patterns, see: → references/migration-guide.md