5 Common Mistakes When Migrating from EJB to Spring Boot

Introduction

Over the past decade, I've guided dozens of organizations through EJB to Spring Boot migrations. While every legacy system has its quirks, I see the same mistakes repeated across different companies. This post shares the five most common pitfalls and how to avoid them.

Mistake #1: Starting Without Understanding Dependencies

The Problem: Teams dive into code without mapping how their EJBs interact. Three months later, they discover their "simple" user service calls 47 other EJBs through complex dependency chains.

What Happens: Migration stalls. The "easy" module turns out to be tightly coupled with half the application. Leadership loses confidence.

The Fix: Before writing any Spring Boot code:

1. Generate a dependency graph of your EJBs
2. Identify leaf nodes (EJBs with no dependencies)
3. Start with isolated modules
4. Work your way up the dependency tree

Real Example: A client wanted to migrate their reporting service first because "it's critical." Analysis revealed it depended on 30+ other EJBs. We started with the email notification service instead—zero dependencies, high value, completed in 2 weeks.

Mistake #2: Treating It Like a Rewrite

The Problem: Teams see migration as a chance to "do it right this time" and start redesigning the architecture, refactoring business logic, and adding new features.

What Happens: Scope creeps. Timelines explode. The migration becomes a multi-year project. Eventually canceled.

The Fix: Migration and improvement are separate activities:

1. Migrate first: Move logic from EJB to Spring Boot preserving behavior
2. Test thoroughly: Ensure nothing broke
3. Then improve: Refactor, optimize, add features

Keep them separate or you'll never finish.

Real Example: One team decided to migrate their order processing system AND implement event sourcing AND add real-time analytics. Eighteen months later, nothing was in production. We rolled back, did a simple lift-and-shift migration in 3 months, then added improvements incrementally.

Mistake #3: Ignoring Transaction Boundaries

The Problem: EJB container-managed transactions are implicit. Developers don't realize the old code relied on transaction boundaries they never explicitly defined.

What Happens: Data corruption. Race conditions. Mysterious bugs that only appear in production under load.

The Fix:

1. Document existing transaction boundaries before migrating
2. Use @Transactional explicitly in Spring Boot
3. Understand propagation levels (REQUIRED, REQUIRES_NEW, etc.)
4. Test transactional behavior thoroughly

Code Example:

// Old EJB - implicit transaction
@Stateless
public class OrderService {
    public void createOrder(Order order) {
        // Transaction automatically started by container
        em.persist(order);
        notificationService.sendEmail(order);
        // Transaction committed automatically
    }
}

// Spring Boot - make it explicit
@Service
public class OrderService {
    @Transactional  // Don't forget this!
    public void createOrder(Order order) {
        orderRepository.save(order);
        notificationService.sendEmail(order);
    }
}

Mistake #4: Converting Everything to REST APIs

The Problem: Teams assume "modern = REST APIs everywhere" and convert all EJB remote calls to HTTP calls.

What Happens:

• Chatty network calls destroy performance
• Serialization overhead slows everything down
• Distributed transaction nightmares
• Debugging becomes incredibly difficult

The Fix: Just because you can make it REST doesn't mean you should:

1. Same JVM: Use direct method calls (Spring @Service)
2. Different JVMs: Consider RMI initially, migrate to REST later
3. External clients: REST/GraphQL makes sense

Don't distribute your monolith prematurely.

Real Example: A client converted 200+ EJB remote interfaces to REST endpoints. Performance dropped by 70%. We consolidated 80% back into direct service calls and kept REST only for actual external APIs.

Mistake #5: Skipping the Testing Infrastructure

The Problem: Legacy EJB apps often have minimal automated tests. Teams migrate without fixing this first.

What Happens: Every change is terrifying. No confidence in the migration. Bugs slip through to production.

The Fix: Build testing infrastructure BEFORE migrating:

1. Integration tests first: Test existing EJB behavior
2. Capture current behavior: Even if it's buggy, document it
3. Parallel testing: Run same tests against EJB and Spring Boot
4. Gradually add unit tests: As you migrate modules

Testing Strategy:

// Test BOTH implementations during migration
@SpringBootTest
class UserServiceMigrationTest {

    @Test
    void testSameBehavior() {
        // Test against old EJB
        User ejbResult = legacyUserEJB.getUser(123);

        // Test against new Spring Boot service
        User springResult = userService.getUser(123);

        // Assert they behave identically
        assertEquals(ejbResult, springResult);
    }
}

Bonus Mistake: Forgetting About Operations

Your ops team knows how to monitor WebLogic. They don't know Spring Boot actuators, micrometer metrics, or embedded Tomcat tuning. Include them early or deployment will be painful.

Conclusion

EJB to Spring Boot migration is achievable, but it's not just a code translation exercise. It requires:

• Understanding your system architecture
• Maintaining business continuity
• Respecting transaction boundaries
• Making thoughtful distribution decisions
• Building comprehensive tests

Avoid these mistakes and your migration will be faster, cheaper, and less risky.

Planning an EJB migration? Get an expert assessment to avoid these costly mistakes.