java使用软引用实现缓存机制示例

public class GoodsBase {
    private static Map<String, Goods> base = new HashMap<>();
    public static Map<String, Goods> getBase() {
        return base;
    }
}

public class GoodsCache {
    private volatile static GoodsCache goodsCache;
    public GoodsCache(){
        this.cache = new HashMap<>();
    }
    public static GoodsCache getGoodsCache() {
        if(goodsCache == null) {
            synchronized (GoodsCache.class){
                if(goodsCache == null){
                    goodsCache = new GoodsCache();
                }
            }
        }
        return goodsCache;
    }
    // 将缓存对象存储在软引用中
    private Map<String, SoftReference<Goods>> cache;
    // 根据id存储缓存Goods对象
    public void setCache(Goods goods) {
        cache.put(goods.getId(), new SoftReference<Goods>(goods));
        System.out.println("添加数据到缓存成功");
    }
    // 根据id从缓存中获取对象
    public Goods getCache(String id) {
        // 根据id，获取缓存对象的软引用
        SoftReference<Goods> softRef = cache.get(id);
        return softRef == null ? null : softRef.get();
    }
    public void delCache(String id) {
        cache.remove(id);
        System.out.println("从缓存删除数据成功");
    }
}

public class GoodsService {
    GoodsCache goodsCache = GoodsCache.getGoodsCache();
    public Goods getById(String id){
        if(goodsCache.getCache(id) == null){
            Goods goods = GoodsBase.getBase().get(id);
            goodsCache.setCache(goods);
            System.out.println("从数据库读取数据");
            System.out.println(goods.getName());
            return goods;
        }
        System.out.println(goodsCache.getCache(id).getName());
        return goodsCache.getCache(id);
    }
    public void add(Goods goods){
        goodsCache.setCache(goods);
        GoodsBase.getBase().put(goods.getId(), goods);
        System.out.println("添加数据到数据库");
    }
    public void deleteById(String id){
        if(goodsCache.getCache(id) != null){
            goodsCache.delCache(id);
        }
        GoodsBase.getBase().remove(id);
    }
}