记一次软引用SoftReference做缓存的漏洞修复及验证

悠悠 2022-12-30 07:51 45阅读 0赞

框架底层的Excel导入组件实现中**使用SoftReference软引用做缓存**，将Excel导入对应类的字段等注解配置信息做了缓存。

开发测试都没问题，但是程序部署时间长了导入功能就用不了报错。排查定位到为该缓存失效导致的。

**原代码：**

public final class BeanUtils {
        /**
         * 申明软引用以便内存溢出的时候回收.
         */
        private SoftReference<Map<Class<?>, Map<String, PropertyDescriptor>>> propertyDescriptorCache
                = new SoftReference<>(new ConcurrentHashMap<>());
    
        private BeanUtils() {
        }
    
    
         /**
         * 根据类名和字段获取对应属性操作用作后续调用读写方法.
         *
         * @param clz       java类.
         * @param fieldName 字段值.
         * @return
         */
        public PropertyDescriptor getFieldProperty(Class<?> clz, @NonNull String fieldName) throws IntrospectionException {
            Map<Class<?>, Map<String, PropertyDescriptor>> cache = propertyDescriptorCache.get();
            Map<String, PropertyDescriptor> descriptorMap = cache.get(clz);//bug点
            if (descriptorMap == null || descriptorMap.get(fieldName) == null) {
                //不存在.
                descriptorMap = new ConcurrentHashMap<>();
                // 添加所有字段进入.
                PropertyDescriptor[] propertyDescriptors = getBeanInfo(clz).getPropertyDescriptors();
                Map<String, PropertyDescriptor> finalDescriptorMap = descriptorMap;
                // 一次载入所有字段描述.
                Arrays.stream(propertyDescriptors).forEach(descriptor -> {
                    finalDescriptorMap.put(descriptor.getName(), descriptor);
                });
            }
    
            //返回缓存的描述.
            return descriptorMap.get(fieldName);
        }
    
    ……
    }

**修复优化代码：**

public PropertyDescriptor getFieldProperty(Class<?> clz, @NonNull String fieldName) throws IntrospectionException {
            //logger.info("Excel导入缓存propertyDescriptorCache值为：{}",gson.toJson(propertyDescriptorCache));
            Map<Class<?>, Map<String, PropertyDescriptor>> cache = propertyDescriptorCache.get();
            logger.debug("Excel导入缓存cache值为：{}",cache);
            if(cache == null){
                logger.info("Excel导入缓存cache值为null");
                propertyDescriptorCache = new SoftReference<>(new ConcurrentHashMap<>());
                cache = propertyDescriptorCache.get();
            }
            Map<String, PropertyDescriptor> descriptorMap = cache.get(clz);
            if (descriptorMap == null || descriptorMap.get(fieldName) == null) {
                //不存在.
                descriptorMap = new ConcurrentHashMap<>();
                // 添加所有字段进入.
                PropertyDescriptor[] propertyDescriptors = getBeanInfo(clz).getPropertyDescriptors();
                Map<String, PropertyDescriptor> finalDescriptorMap = descriptorMap;
                // 一次载入所有字段描述.
                Arrays.stream(propertyDescriptors).forEach(descriptor -> {
                    finalDescriptorMap.put(descriptor.getName(), descriptor);
                });
                //放进去！
                cache.put(clz,descriptorMap);
            }
    
            //返回缓存的描述.
            return descriptorMap.get(fieldName);
        }

**调试验证：**

在调用导入的接口结束位置加了代码触发GC使软引用被回收：

List list = new ArrayList();
            for(int i=0;i<200;i++){
                byte[] allocation = new byte[60000*1024];
                list.add(allocation);
            }

**正常的软引用缓存：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70][]

**GC:**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70 1][]

**被回收了的软引用缓存：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70 2][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70 3][]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20201224140652720.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/20201224140801415.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0d3htaW5n,size_16,color_FFFFFF,t_70