Switching Java frameworks is a significant undertaking for any development team.
While Spring Boot has long been a dominant force in the Java ecosystem, its complexity and slower startup times have led many to seek leaner, more efficient alternatives.
Avaje is emerging as a powerful contender, offering impressive performance gains and a simplified development experience.
A successful Java framework migration requires careful planning and a clear understanding of the steps involved.
This guide provides a detailed walkthrough for developers considering or currently undertaking a Spring migration from Spring Boot to Avaje.
We will cover the core differences between the two frameworks, outline a step-by-step migration process, and offer best practices to ensure a smooth transition.
By following these steps, you can leverage Avaje’s modern features to build faster, more maintainable applications while minimizing disruption to your development workflow.
Understanding the Core Differences
Before starting the migration, it’s essential to grasp the fundamental distinctions between Spring Boot and Avaje. This knowledge will inform your migration strategy and help you adapt to Avaje’s unique architecture.
Dependency Injection Models
- Spring Boot: Uses a powerful but complex dependency injection (DI) container. It relies heavily on classpath scanning and reflection at runtime, which can contribute to slower application startup and increased memory usage. Configuration is often managed through annotations (@Component, @Autowired) and XML or Java-based configuration files.
- Avaje Inject: Employs a compile-time DI approach using a Java annotation processor. This model generates DI wiring at compile time, eliminating the need for runtime reflection and classpath scanning. The result is significantly faster startup times and a smaller memory footprint, as the dependency graph is resolved before the application even runs.
Application Configuration
- Spring Boot: Features a comprehensive configuration system using application.properties or application.yml files, environment variables, and profiles. This system is flexible but can become complex to manage in large applications.
- Avaje: Utilizes a simpler, more direct configuration approach. It often uses a combination of Java-based configuration and standard .properties or .yaml files. The focus is on explicitness and simplicity, reducing the layers of abstraction found in Spring.
Preparing for the Migration
A successful migration begins with thorough preparation. This phase involves assessing your current application, setting up the new project structure, and identifying dependencies that will need to be replaced or adapted.
Auditing Your Spring Boot Application
- Identify Core Dependencies: Create a comprehensive list of all Spring Boot starters and third-party libraries your project uses. Pay close attention to modules like Spring Data, Spring Security, and Spring Web.
- Analyze Custom Configurations: Document all custom configurations, including @Configuration classes, property sources, and profiles. You will need to replicate this logic using Avaje’s configuration mechanisms.
- Review Business Logic: Ensure your business logic is loosely coupled from the Spring framework. Services and components that are heavily reliant on Spring-specific features will require more significant refactoring.
Setting Up the Avaje Project
- Build Tool Configuration: Update your pom.xml (Maven) or build.gradle (Gradle) file. Remove Spring Boot dependencies and add the necessary Avaje modules, including avaje-inject and avaje-http.
- Annotation Processor: Crucially, you must configure the Java annotation processor for avaje-inject. This processor is responsible for generating the compile-time dependency injection code.
Migrating Dependency Injection
This is the most critical part of the Spring migration. You will replace Spring’s DI annotations and container with Avaje Inject’s compile-time equivalent.
Replacing Spring Annotations
- @Component, @Service, @Repository: Replace these with Avaje’s @Singleton annotation. This tells the Avaje annotation processor that the class should be managed as a singleton bean.
- @Autowired: Replace field, constructor, or method injection using @Autowired with constructor injection in your @Singleton classes. Avaje Inject strongly prefers constructor injection, which promotes immutability and clearer dependency management.
- @Configuration and @Bean: Replicate the logic from your @Bean methods. For simple object creation, you can annotate the class with @Singleton. For more complex factory logic, you can create a factory class annotated with @Factory, with methods annotated by @Bean.
Example: Migrating a Service
Spring Boot:
@Service
public class MyService {
private final MyRepository repository;
@Autowired
public MyService(MyRepository repository) {
this.repository = repository;
}
// … business logic
}
Avaje:
@Singleton
public class MyService {
private final MyRepository repository;
public MyService(MyRepository repository) {
this.repository = repository;
}
// … business logic
}
Adapting the Web Layer
Next, you’ll migrate your web controllers from Spring Web MVC to Avaje HTTP. Avaje HTTP is a lightweight web framework that integrates seamlessly with Avaje Inject.
Converting Controllers
- @RestController: Replace this with Avaje’s @Controller annotation. This marks the class as a web controller.
- @RequestMapping, @GetMapping, @PostMapping: These annotations have direct equivalents in Avaje HTTP. For example, @GetMapping(“/users”) remains functionally the same.
- @RequestBody, @PathVariable, @RequestParam: Avaje HTTP uses similar annotations to bind request data to method parameters. The migration is often a simple one-to-one replacement.
Example: Migrating a Controller
Spring Boot:
@RestController
@RequestMapping(“/api/tasks”)
public class TaskController {
@GetMapping(“/{id}”)
public Task getTask(@PathVariable Long id) {
// … logic
}
}
Avaje:
@Controller
@Path(“/api/tasks”) // Avaje uses @Path for base path
public class TaskController {
@Get(“/{id}”) // Avaje uses @Get, @Post, etc.
public Task getTask(@PathSegment Long id) { // Note the annotation difference
// … logic
}
}
Handling Data Persistence
If your application uses Spring Data, you’ll need to migrate to an alternative persistence solution that works well with Avaje.
Avaje Ebean is a natural choice, as it’s part of the same ecosystem and designed for high performance.
From Spring Data JPA to Avaje Ebean
- Entity Annotations: Ebean uses standard Jakarta Persistence annotations (@Entity, @Id, @Column), so your existing entities will require minimal changes. You may need to add Avaje-specific annotations like @DbName for multi-database setups.
- Repository Pattern: Spring Data’s repository interfaces are a powerful abstraction. You can replicate this pattern in Avaje by creating your own repository classes. These repositories will be @Singleton beans that use Ebean’s Database object to perform CRUD operations.
- Database Queries: Convert Spring Data query methods and @Query annotations to Ebean’s query language (EQL) or its programmatic query builder. Ebean’s queries are type-safe and validated at compile time.
Finalizing and Testing the Migration
With the core components migrated, the final steps involve wiring everything together, testing thoroughly, and deploying the new application.
The Application Main Class
- Replace SpringApplication.run(): Your main application entry point will no longer use Spring’s bootstrap mechanism. Instead, you will use Avaje.inject().build() to initialize the DI container and start any necessary services, like the Avaje HTTP server.
Comprehensive Testing
- Unit Tests: Update your unit tests to remove Spring’s testing framework. Since Avaje promotes constructor injection, mocking dependencies for unit tests becomes much simpler. You can use standard mocking libraries like Mockito without needing a Spring context.
- Integration Tests: Write new integration tests using Avaje’s testing support. You can start a full application context to test the interactions between your controllers, services, and repositories in a realistic environment.
- Performance Testing: One of the main goals of this Java framework migration is to improve performance. Conduct load testing and measure startup times to quantify the improvements and ensure the new application meets your performance goals.
Your Path to a Modern Java Application
Migrating from Spring Boot to Avaje is more than a technical exercise; it’s a strategic move toward building faster, more resource-efficient Java applications.
By replacing runtime reflection with a compile-time DI model, Avaje Inject provides a significant performance boost and a simpler developer experience.
While the process requires careful planning and execution, the benefits of faster startup times, lower memory consumption, and a more streamlined codebase are well worth the effort.
By following the steps outlined in this guide, your team can confidently navigate the migration process.
Ready to take the next step? Explore the official Avaje documentation and start building a proof-of-concept to see the benefits for yourself.