深入理解Spring单例Bean的内存占用与高效管理策略

import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;
import java.util.HashMap;
import java.util.Map;

@Service
public class DataService {

    // 模拟数据源
    private Map<String, String> dataStore = new HashMap<>();

    public DataService() {
        dataStore.put("key1", "value1");
        dataStore.put("key2", "value2");
        dataStore.put("key3", "value3");
    }

    /**
     * 模拟从耗时数据源获取数据，并使用缓存
     * @param id 数据标识符
     * @return 对应的数据
     */
    @Cacheable(value = "myCache", key = "#id")
    public String getData(String id) {
        System.out.println("Fetching data for id: " + id + " from actual source...");
        // 模拟耗时操作或数据库查询
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        return dataStore.get(id);
    }
}

import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import org.springframework.stereotype.Service;
import java.util.concurrent.TimeUnit;

@Service
public class ProductService {

    // 定义一个Caffeine缓存实例，设置过期时间和最大容量
    private final Cache<String, Product> productCache = Caffeine.newBuilder()
            .expireAfterWrite(10, TimeUnit.MINUTES) // 写入后10分钟过期
            .maximumSize(10_000) // 最大缓存条目数
            .build();

    /**
     * 根据产品ID获取产品信息，优先从缓存获取
     * @param productId 产品ID
     * @return 产品对象
     */
    public Product getProductById(String productId) {
        // 尝试从缓存获取
        Product product = productCache.getIfPresent(productId);
        if (product != null) {
            System.out.println("Getting product " + productId + " from cache.");
            return product;
        }

        // 缓存中没有，从数据库加载
        System.out.println("Getting product " + productId + " from database.");
        product = loadProductFromDatabase(productId); // 模拟从数据库加载
        productCache.put(productId, product); // 放入缓存
        return product;
    }

    // 模拟从数据库加载产品的方法
    private Product loadProductFromDatabase(String productId) {
        // 模拟数据库查询耗时
        try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        return new Product(productId, "Product Name " + productId);
    }

    // 示例产品类
    static class Product {
        String id;
        String name;

        public Product(String id, String name) {
            this.id = id;
            this.name = name;
        }

        public String getId() { return id; }
        public String getName() { return name; }

        @Override
        public String toString() {
            return "Product{id='" + id + "', name='" + name + "'}";
        }
    }
}