10 Common Mistakes Java Developers Make with Spring Boot (and How to Avoid Them)

Spring Boot has made Java development faster and easier. But with its simplicity comes room for subtle mistakes — ones that can cause performance issues, security vulnerabilities, or architectural debt.

In this blog, I’ll walk you through 10 common mistakes Java developers make with Spring Boot and how to avoid them. Whether you're a beginner or an experienced developer, you'll find something useful here.

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1️⃣ Ignoring application.properties vs application.yml Structure

Using both formats interchangeably without consistency leads to messy configuration and bugs.

❌ Mistake: Mixing application.properties and application.yml

✅ Fix: Stick to one format (preferably YAML for better readability), and keep profiles (dev, prod, test) cleanly separated.

# application-dev.yml

server:

port: 8081

spring:

datasource:

url: jdbc:mysql://localhost:3306/devdb

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2️⃣ Misusing @Autowired Everywhere

❌ Mistake: Using @Autowired field injection

Field injection is hard to test and not recommended.

✅ Fix: Use constructor injection instead. It’s cleaner and supports immutability and unit testing.

private final UserService userService;

public UserController(UserService userService) {

this.userService = userService;

}

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3️⃣ Not Using DTOs in API Layers

❌ Mistake: Returning JPA entities directly in REST responses.

This tightly couples the DB model with external APIs.

✅ Fix: Create DTO (Data Transfer Object) classes to send and receive data.

public class UserDTO {

private String name;

private String email;

}

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4️⃣ Hardcoding Values Instead of Using Configuration

❌ Mistake: Hardcoding URLs, keys, or limits.

✅ Fix: Externalize all configuration in application.yml and inject them using @Value or @ConfigurationProperties.

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5️⃣ Not Handling Exceptions Gracefully

❌ Mistake: Letting exceptions leak as 500 errors.

✅ Fix: Use @ControllerAdvice to handle errors globally and return consistent error responses.

@RestControllerAdvice

public class GlobalExceptionHandler {

@ExceptionHandler(ResourceNotFoundException.class)

public ResponseEntity<?> handleNotFound(ResourceNotFoundException ex) {

return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.getMessage());

}

}

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6️⃣ Ignoring Profiles for Environment-Specific Configs

❌ Mistake: One config for all environments.

✅ Fix: Use Spring Profiles like dev, qa, prod with application-{profile}.yml files.

Start app with:

-Dspring.profiles.active=prod

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7️⃣ Not Securing Endpoints with Spring Security

❌ Mistake: All APIs are public by default.

✅ Fix: Use Spring Security and explicitly allow only certain endpoints.

@Override

protected void configure(HttpSecurity http) throws Exception {

http

.authorizeRequests()

.antMatchers("/public/**").permitAll()

.anyRequest().authenticated();

}

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8️⃣ Overusing @ComponentScan

❌ Mistake: Scanning unnecessary packages, slowing startup.

✅ Fix: Limit @ComponentScan to only the required base packages.

@ComponentScan(basePackages = {"com.example.app"})

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9️⃣ Not Monitoring or Logging Properly

❌ Mistake: Using System.out.println for debugging.

✅ Fix: Use SLF4J with Logback or Log4j2 for structured logs. Also, integrate with Actuator + Prometheus + Grafana for monitoring.

private static final Logger logger = LoggerFactory.getLogger(MyClass.class);

logger.info("Processing user {}", userId);

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🔟 Not Writing Tests

❌ Mistake: Skipping tests entirely or writing only happy-path tests.

✅ Fix: Write unit tests with JUnit + Mockito and integration tests using @SpringBootTest.

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✅ Final Thoughts

Spring Boot is a powerful tool, but it’s easy to misuse it if you don't follow best practices. By avoiding these common pitfalls, you'll write more maintainable, testable, and secure code.

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