spring-boot-migration

Spring Boot 2 to 3 Migration Skill

Overview

This skill provides guidance for migrating Spring Boot applications from version 2.x to 3.x, which is one of the most significant upgrades in Spring Boot history due to the Java EE to Jakarta EE transition.

Key Migration Steps

1. Update Spring Boot Version

Change the parent POM version:

<!-- Before: Spring Boot 2.7.x -->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.7.18</version>
</parent>

<!-- After: Spring Boot 3.2.x -->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.2.0</version>
</parent>

2. Update Java Version

Spring Boot 3 requires Java 17 or later:

<properties>
    <!-- Before -->
    <java.version>1.8</java.version>

    <!-- After -->
    <java.version>21</java.version>
</properties>

3. Remove Deprecated Dependencies (CRITICAL: JAXB API)

You MUST remove the old javax.xml.bind:jaxb-api dependency. This is a Java EE dependency that was commonly added for Java 9+ compatibility in Spring Boot 2.x projects, but it conflicts with Jakarta EE in Spring Boot 3.

Dependencies to REMOVE from pom.xml

<!-- REMOVE ALL OF THESE - they are incompatible with Spring Boot 3 -->

<!-- Old JAXB API - MUST BE REMOVED -->
<dependency>
    <groupId>javax.xml.bind</groupId>
    <artifactId>jaxb-api</artifactId>
</dependency>

<!-- Old JAXB Implementation - MUST BE REMOVED -->
<dependency>
    <groupId>com.sun.xml.bind</groupId>
    <artifactId>jaxb-impl</artifactId>
</dependency>

<dependency>
    <groupId>com.sun.xml.bind</groupId>
    <artifactId>jaxb-core</artifactId>
</dependency>

<!-- Old Java Activation - MUST BE REMOVED -->
<dependency>
    <groupId>javax.activation</groupId>
    <artifactId>activation</artifactId>
</dependency>

<dependency>
    <groupId>javax.activation</groupId>
    <artifactId>javax.activation-api</artifactId>
</dependency>