Bean Scopes in Spring - Advanced Guide

1️⃣ Introduction

Bean scopes in Spring define how bean instances are created and managed throughout the application lifecycle. This article explores different scopes and their use cases.

Key features include:

  • Singleton scope (default)
  • Prototype scope
  • Request scope
  • Session scope
  • Application scope
  • WebSocket scope

2️⃣ Key Concepts & Terminology

  • Singleton: Single instance per Spring container
  • Prototype: New instance for each request
  • Request: Single instance per HTTP request
  • Session: Single instance per HTTP session
  • Application: Single instance per ServletContext
  • WebSocket: Single instance per WebSocket session

3️⃣ Hands-on Implementation 🛠

🔹 Step 1: Singleton Scope

@Service
@Scope("singleton")  // Default scope
public class CacheService {
    private Map cache = new HashMap<>();
    
    public void put(String key, Object value) {
        cache.put(key, value);
    }
    
    public Object get(String key) {
        return cache.get(key);
    }
}

🔹 Step 2: Prototype Scope

@Component
@Scope("prototype")
public class UserPreferences {
    private String theme;
    private String language;
    
    public void setTheme(String theme) {
        this.theme = theme;
    }
    
    public void setLanguage(String language) {
        this.language = language;
    }
}

🔹 Step 3: Request Scope

@Component
@Scope(value = "request", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class RequestContext {
    private String requestId;
    private LocalDateTime timestamp;
    
    public void setRequestId(String requestId) {
        this.requestId = requestId;
    }
    
    public void setTimestamp(LocalDateTime timestamp) {
        this.timestamp = timestamp;
    }
}

4️⃣ Common Issues & Debugging 🐞

Common Issues and Solutions

Issue Solution
Prototype beans in singleton Use ScopedProxyMode.TARGET_CLASS
Memory leaks in prototype Implement proper cleanup in destroy methods
Scope not working Check proxy mode and scope configuration

5️⃣ Q&A / Frequently Asked Questions

The default scope in Spring is singleton. This means only one instance of the bean is created per Spring container.

Use prototype scope when you need a new instance of the bean for each request or when the bean maintains state that shouldn't be shared between different parts of the application.

6️⃣ Best Practices & Pro Tips 🚀

  • Use singleton scope for stateless beans
  • Use prototype scope for stateful beans
  • Consider memory implications of different scopes
  • Use appropriate proxy modes
  • Implement proper cleanup for prototype beans

7️⃣ Read Next 📖

8️⃣ Conclusion

Understanding bean scopes is crucial for building efficient and maintainable Spring applications. Each scope serves a specific purpose and has its own implications for memory usage and state management.

Remember to choose the appropriate scope based on your application's requirements and consider the impact on performance and resource usage.

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