项目重新部署后报The attribute required is undefined for the annotation type XmlElementRef

在另外一台机器上部署项目,项目导进Eclipse中发现有异常

public class BooleanFeatureType
    extends FeatureBaseType{

    @XmlElementRef(name = "Value", namespace = "http://schemas.sean.com/ma/CA/OPM/", 
			type = JAXBElement.class, required = false)
    protected JAXBElement<Boolean> value;
......

@XmlElementRef那行报错：The attribute required is undefined for the annotation type XmlElementRef

解决办法：打开项目 java build path>order and export 将 JRE system library 置顶。错误消失