Java使用WeakHashMap实现缓存自动清理

import java.util.Map;
import java.util.WeakHashMap;

public class DatabaseCache {

    // 使用 WeakHashMap 存储查询结果缓存
    private Map<String, String> cache = new WeakHashMap<>();

    // 模拟从数据库获取数据
    public String getDataFromDatabase(String query) {
        // 首先检查缓存中是否已有结果
        String result = cache.get(query);
        if (result != null) {
            System.out.println("Cache hit for query: " + query);
            return result;
        }
        
        // 模拟执行数据库查询
        System.out.println("Querying database for: " + query);
        result = "Result for query: " + query;

        // 将结果存入缓存
        cache.put(query, result);

        return result;
    }

    public static void main(String[] args) {
        DatabaseCache dbCache = new DatabaseCache();

        String query1 = "SELECT * FROM users";
        String query2 = "SELECT * FROM products";

        // 第一次查询，缓存未命中
        System.out.println(dbCache.getDataFromDatabase(query1));
        System.out.println(dbCache.getDataFromDatabase(query2));

        // 再次查询，缓存命中
        System.out.println(dbCache.getDataFromDatabase(query1));

        // 手动断开对查询条件的强引用，模拟不再需要缓存的情况
        query1 = null;

        // 显式触发垃圾回收
        System.gc();

        // 等待一些时间，确保 GC 执行
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // 查询缓存中已被清理的数据
        System.out.println("Cache after GC: " + dbCache.cache);
    }
}

Querying database for: SELECT * FROM users
Querying database for: SELECT * FROM products
Cache hit for query: SELECT * FROM users
Cache after GC: {SELECT * FROM products=Result for query: SELECT * FROM products}