ReferencePropertyInfoImpl.java 文件源码

/**
 * Reads the value of {@code XmlElementRef.required()}.
 *
 * If we are working as 2.1 RI, this defaults to true.
 */
private boolean isRequired(XmlElementRef ref) {
    if(!is2_2)  return true;

    try {
        return ref.required();
    } catch(LinkageError e) {
        is2_2 = false;
        return true;    // the value defaults to true
    }
}