required attribute

基本解释

Many attributes have default values, but only the required attribute must be assigned a value.
许多属性具有缺省值，但只有必需属性必须分配值。
When you use this form of the c:forEach> tag, the items attribute is the only required attribute.
当使用这种形式的 c:forEach> 标记时， items 属性是唯一必需的属性。
Unlike the REQUIRED attribute, the MANDATORY attribute will not start a transaction if one does not exist, but rather will throw an exception indicating that a transaction is required.
与 REQUIRED 属性不同，MANDATORY 属性将不会开始不存在的事务，而是抛出一个异常，指示需要事务。