Spring的BeanUtils.getPropertyDescriptors 學習

/**
 * 類中的某些字段不校驗  並返回空字段名
 */
public static List<String> validateProperty(Object validateObj, String... ignoreProperties) {
    PropertyDescriptor[] targetPds = BeanUtils.getPropertyDescriptors(validateObj.getClass());
    List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);
    List<String> errList = new ArrayList<>();
    for (PropertyDescriptor targetPd : targetPds) {
        Method readMethod = targetPd.getReadMethod();
        if (readMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
            try {
                if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
                    readMethod.setAccessible(true);
                }
                Object value = readMethod.invoke(validateObj);
                if (value instanceof String) {
                    if (StrUtil.isEmpty((String) value)) {
                        errList.add(validateObj.getClass().getSimpleName() + "中的" + targetPd.getName() + "不能為空");
                        continue;
                    }
                }
                if (value == null) {
                    errList.add(validateObj.getClass().getSimpleName() + "中的" + targetPd.getName() + "不能為空");
                }

                if (!targetPd.getName().equals("class"))
                    map.put(targetPd.getName(), value);

            } catch (Throwable ex) {
                throw new FatalBeanException(
                        "Could not copy property '" + targetPd.getName() + "' from source to target", ex);
            }
        }
    }

    map.forEach((k, v) -> {
        System.out.println(k + ":" + v);
    });
    return errList;

}
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偶得如上代碼 用以拿到一個類中的所有字段名和對應的值
直接看代碼 找到了

static CachedIntrospectionResults forClass(Class<?> beanClass) throws BeansException {
   CachedIntrospectionResults results = strongClassCache.get(beanClass);
   if (results != null) {
      return results;
   }
   results = softClassCache.get(beanClass);
   if (results != null) {
      return results;
   }

   results = new CachedIntrospectionResults(beanClass);
   ConcurrentMap<Class<?>, CachedIntrospectionResults> classCacheToUse;

   if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader()) ||
         isClassLoaderAccepted(beanClass.getClassLoader())) {
      classCacheToUse = strongClassCache;
   }
   else {
      if (logger.isDebugEnabled()) {
         logger.debug("Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe");
      }
      classCacheToUse = softClassCache;
   }

　　// 在這一行之后 強引用Map添加了緩存

   CachedIntrospectionResults existing = classCacheToUse.putIfAbsent(beanClass, results);
   return (existing != null ? existing : results);
}

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因此 當對象第一次來的時候 反射創建 后續走到之后 就會走緩存了