Introduction

Spring Boot provides a powerful dependency injection mechanism, but improper configuration of bean scopes can lead to memory leaks, redundant object creation, and performance degradation. Issues such as using prototype-scoped beans in singleton beans, misusing application context, and excessive autowiring can result in high memory consumption and CPU load. This article explores common causes of memory leaks and CPU spikes in Spring Boot, debugging techniques, and best practices for optimizing dependency injection and resource management.

Common Causes of Memory Leaks and High CPU Usage

1. Misuse of Prototype Beans in Singleton Beans

Injecting a prototype-scoped bean into a singleton-scoped bean results in a single instance of the prototype bean being reused, leading to unintended state retention.

Problematic Scenario

@Component
public class SingletonService {
    @Autowired
    private PrototypeComponent prototypeComponent;

    public void execute() {
        prototypeComponent.performTask();
    }
}

@Component
@Scope("prototype")
public class PrototypeComponent {
    public void performTask() {
        System.out.println("Executing task");
    }
}

Since `PrototypeComponent` is injected once into `SingletonService`, the same instance is used across all calls, defeating the purpose of the prototype scope.

Solution: Use `ObjectProvider` to Retrieve New Instances

@Component
public class SingletonService {
    @Autowired
    private ObjectProvider prototypeProvider;

    public void execute() {
        PrototypeComponent prototypeComponent = prototypeProvider.getObject();
        prototypeComponent.performTask();
    }
}

Using `ObjectProvider` ensures that a new instance of `PrototypeComponent` is created on every method call.

2. Excessive Autowiring Leading to Circular Dependencies

Circular dependencies occur when two or more beans depend on each other, causing memory leaks and high CPU usage due to redundant bean initialization.

Problematic Scenario

@Component
public class ServiceA {
    @Autowired
    private ServiceB serviceB;
}

@Component
public class ServiceB {
    @Autowired
    private ServiceA serviceA;
}

Spring Boot detects circular dependencies and may either fail or create proxy objects, leading to high CPU usage and memory retention.

Solution: Use `@Lazy` Injection to Break Circular Dependencies

@Component
public class ServiceA {
    @Autowired
    @Lazy
    private ServiceB serviceB;
}

Using `@Lazy` defers the initialization of the dependent bean, preventing circular dependencies and unnecessary CPU load.

3. Improper Use of `@RequestScope` Beans in Singleton Services

Injecting a request-scoped bean into a singleton bean can cause memory retention issues and unexpected behavior.

Problematic Scenario

@Component
public class GlobalService {
    @Autowired
    private RequestScopedBean requestScopedBean;
}

@Component
@RequestScope
public class RequestScopedBean {
    public String getRequestInfo() {
        return "Request Data";
    }
}

Since `GlobalService` is a singleton, it holds a reference to a request-scoped bean that should be created per request, leading to memory leaks.

Solution: Use `ObjectProvider` for Request-Scoped Beans

@Component
public class GlobalService {
    @Autowired
    private ObjectProvider requestScopedBeanProvider;

    public void processRequest() {
        RequestScopedBean requestScopedBean = requestScopedBeanProvider.getObject();
        System.out.println(requestScopedBean.getRequestInfo());
    }
}

Using `ObjectProvider` ensures that a new request-scoped bean instance is retrieved per request.

4. High CPU Usage Due to Unbounded Thread Pools

Improper configuration of thread pools can lead to excessive thread creation, causing CPU spikes and memory exhaustion.

Problematic Scenario

@Service
public class TaskService {
    @Async
    public void executeTask() {
        // Long-running process
    }
}

Using `@Async` without configuring a thread pool leads to unbounded thread creation, causing high CPU usage.

Solution: Define a Thread Pool for Async Execution

@Configuration
@EnableAsync
public class AsyncConfig {
    @Bean
    public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(25);
        executor.initialize();
        return executor;
    }
}

Configuring a thread pool ensures optimal CPU utilization and prevents excessive thread creation.

Best Practices for Managing Bean Scope and Performance in Spring Boot

1. Use `ObjectProvider` for Prototype and Request-Scoped Beans

Ensures a new instance is retrieved when needed.

Example:

@Autowired
private ObjectProvider provider;

2. Break Circular Dependencies Using `@Lazy` Injection

Prevents infinite loops in bean initialization.

Example:

@Autowired
@Lazy
private ServiceB serviceB;

3. Limit the Use of Singleton Beans for Stateful Operations

Singletons should be used for stateless services only.

Example:

@Service
public class StatelessService {}

4. Configure Thread Pools for Async Execution

Prevents unbounded thread creation.

Example:

@Bean
public Executor taskExecutor() { ... }

5. Monitor Memory and CPU Usage Using Actuator

Enables real-time performance monitoring.

Example:

management.endpoints.web.exposure.include=metrics,health

Conclusion

Memory leaks and high CPU usage in Spring Boot often result from improper bean scope management, circular dependencies, unbounded thread creation, and incorrect dependency injection. By using `ObjectProvider` for prototype and request-scoped beans, configuring thread pools, breaking circular dependencies with `@Lazy`, and leveraging Spring Boot’s built-in monitoring tools, developers can ensure optimal performance and maintainability in their applications.