Application and problems of Java design patterns in actual projects

Applications and Problems of Design Patterns in Java Development Application Cases: Singleton Pattern: Ensure that a class has only one instance Factory Pattern: Flexibly create complex objects Proxy Pattern: Provide object replacement for access control, caching or delayed loading strategy pattern : Dynamically change the algorithm Observer pattern: Difficulties in implementing loosely coupled event processing: Over-design: Applying too many patterns leads to complex code Improper selection: Wrong pattern selection makes the code difficult to maintain Pattern conflict: Some patterns conflict with each other, the application needs to be cautious and difficult to test : Code testing with complex patterns is difficult

The application and problems of Java design patterns in actual projects

Introduction

Design patterns are libraries of proven, reusable solutions designed to solve common programming problems. They are designed to improve code maintainability, reusability, and extensibility. Design patterns are particularly important in Java development because it is an object-oriented language that provides a powerful and flexible framework for applying design patterns.

Actual cases of design patterns

The following are some Java design patterns that are widely used in actual projects:

• Single Example pattern: Ensure that the class has only one instance, usually used for resource-intensive objects such as database connections or caches.
• Factory pattern: Create objects without specifying specific classes, providing the flexibility to create complex objects.
• Proxy mode: Provide a proxy or replacement for an existing object for access control, caching or lazy loading.
• Strategy mode: Define a series of algorithms and separate the algorithm from the client, allowing the algorithm to be changed dynamically.
• Observer pattern: Allows objects to subscribe to and receive notifications from other objects (topics) to achieve loosely coupled event processing.

The Dilemma of Design Patterns

Although design patterns are very useful, there are also some challenges in practical application:

• Over-design: Applying too many design patterns can make the code complex and difficult to maintain.
• Inappropriate selection: Selecting an inappropriate pattern can lead to code that is difficult to understand and maintain.
• Pattern Conflict: Certain design patterns may conflict with each other and require careful consideration before being applied simultaneously.
• Difficulty in testing: Code with complex design patterns may be difficult to test and require additional testing strategies.

Example: Application of proxy mode in caching

Consider an e-commerce website that needs to cache product data to improve performance. To avoid accessing the database directly, we can use proxy mode:

// 缓存代理类
public class CacheProxy implements ProductRepository {
    private ProductRepository realRepository;
    private Map<Long, Product> cache = new HashMap<>();

    public CacheProxy(ProductRepository realRepository) {
        this.realRepository = realRepository;
    }

    @Override
    public Product findById(Long id) {
        Product product = cache.get(id);
        if (product != null) {
            return product;
        }
        product = realRepository.findById(id);
        cache.put(id, product);
        return product;
    }
}

// 使用缓存代理的客户端
public class ProductController {
    private ProductRepository productRepository;

    public ProductController(ProductRepository productRepository) {
        this.productRepository = productRepository;
    }

    public Product getProductById(Long id) {
        return productRepository.findById(id);
    }
}

By using a caching proxy, we can avoid querying the database every time, thereby improving performance. When product data changes, you can keep the data consistent by clearing the cache.

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