Migrate Application From Spring Boot 2 to Spring Boot 3

With the release of Spring Boot 3, significant changes and improvements have been introduced, particularly around Jakarta EE compliance, Java 17 support, and GraalVM native images. If you are using Spring Boot 2 and are considering migrating to Spring Boot 3, this article will walk you through the necessary steps, considerations, and potential pitfalls during the migration process.

Why Migrate to Spring Boot 3?

Spring Boot 3 is a major release that brings several enhancements, including performance improvements, feature upgrades, and long-term support for modern architectures. Some key highlights include:

• Java 17+ baseline: Spring Boot 3 requires Java 17 or later, removing support for older JDK versions.
• Full Jakarta EE 9+ adoption: This includes namespace changes from javax.* to jakarta.*.
• Improved GraalVM support: Spring Boot 3 offers better performance and compatibility for GraalVM native images.
• Updated libraries: Several outdated libraries have been replaced or updated, and deprecated features have been removed.

However, the upgrade introduces breaking changes, particularly around the transition to Jakarta EE namespaces. Let's dive into how you can successfully migrate your existing Spring Boot 2.x application to Spring Boot 3.x.

Migration Steps

Step 1: Prepare for the Migration

Before starting the migration process, it's essential to ensure that your application is stable and well-tested. Here are a few preparatory steps:

• Ensure comprehensive test coverage: Have a solid suite of unit, integration, and functional tests.
• Create a backup: Back up your project or branch off the current version to ensure a fallback if issues arise.
• Review migration documentation: Read the Spring Boot 3 migration guide to understand the critical changes.

This preparation will provide a solid foundation for detecting and fixing migration-related issues.

Step 2: Update the Dependencies and Java Version

1. Update Spring Boot Dependencies

Depending on whether you're using Maven or Gradle, update your project's parent or build dependencies to point to Spring Boot 3.x.

For Maven, open your pom.xml and modify the parent section:

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.0.0</version> <!-- Use the latest Spring Boot 3.x version -->
</parent>

For Gradle, update the Spring Boot version in your build.gradle:

implementation 'org.springframework.boot:spring-boot-starter:3.x.x'  // Use latest version

2. Upgrade to Java 17 or Later

Spring Boot 3 requires Java 17 or later. If your project is using Java 11 or older, you'll need to upgrade to Java 17.

To check your current Java version, run:

java -version

For Maven, ensure the correct Java version is set in the pom.xml:

<properties>
    <java.version>17</java.version>
</properties>

For Gradle, update the Java version in build.gradle:

sourceCompatibility = '17'
targetCompatibility = '17'

Step 3: Jakarta EE Namespace Migration

One of the most significant changes in Spring Boot 3 is the transition from Java EE (javax.*) to Jakarta EE (jakarta.*).

What’s Changing?

Jakarta EE 9+ introduced a namespace shift. For example, javax.persistence.*, javax.validation.*, and javax.servlet.* have moved to jakarta.persistence.*, jakarta.validation.*, and jakarta.servlet.*, respectively. This is a breaking change and requires code modifications.

How to Migrate?

1. Replace javax.* Imports with jakarta.*:

• Persistence: javax.persistence.* → jakarta.persistence.*
• Validation: javax.validation.* → jakarta.validation.*
• Servlets: javax.servlet.* → jakarta.servlet.*

Example:

// Old import
import javax.persistence.Entity;

// New import
import jakarta.persistence.Entity;

2. Update the Annotations

Update JPA and validation annotations to use the new Jakarta EE imports.

Example:

// Old
@javax.persistence.Entity
public class User { ... }

// New
@jakarta.persistence.Entity
public class User { ... }

3. Third-Party Libraries

Ensure that all dependencies are compatible with Jakarta EE. For instance, if you're using Hibernate, upgrade to Hibernate 6, which is compatible with jakarta.*.

For example:

• Spring Data JPA should be upgraded to the compatible version (Spring Data 2022.x or later).
• Check the libraries for the REST, validation, and other APIs that use the javax.*.

Use tools like mvn dependency:tree (for Maven) or ./gradlew dependencies (for Gradle) to identify any dependencies still relying on javax.* and upgrade them.

Step 4: Review and Update Configuration Files

Some configuration properties have changed between Spring Boot 2 and 3. Review your application.properties or application.yml and update any deprecated properties.

1. Spring Configuration Properties

• Datasource properties: Properties under spring.datasource.* may have updated defaults or new options.
• JPA/Hibernate properties: Spring Boot 3 uses Hibernate 6, which may require updating properties like spring.jpa.*.

2. Logging Configuration

If you have customized logging (e.g., in logback-spring.xml), review the settings as Spring Boot 3 may introduce changes in default logging levels or the underlying library versions.

Step 5: Hibernate 6 and JPA Adjustments

Spring Boot 3 uses Hibernate 6, which introduces its own set of API changes and performance improvements.

Key Changes in Hibernate 6:

• @Enumerated types: The way Hibernate handles @Enumerated types has changed, so review any entity mappings.
• Criteria API: If you're using Hibernate’s Criteria API, check for method signature changes.
• Custom type mappings: Custom database types may need adjustments due to changes in Hibernate's internal type system.

What You Need to Update:

• Ensure all entity classes are updated to use jakarta.persistence.* annotations.
• Test all JPA queries or custom SQL queries to ensure compatibility with Hibernate 6.

Step 6: Test Thoroughly

After migrating, thorough testing is critical to catch migration-related issues. Ensure that:

• Unit, integration, and functional tests: All tests pass without errors.
• Regression testing: Verify that no existing functionality is broken.
• Manual testing: Perform manual checks on critical paths, especially those involving third-party libraries or databases.

Conclusion

Migrating from Spring Boot 2 to Spring Boot 3 can be complex, primarily due to the breaking changes introduced by Jakarta EE. However, with careful planning, testing, and understanding of the changes, the migration process can result in significant performance improvements and a more modern application.