public static Double getDouble(String propertyName, Double defaultValue) {
		Double propertyValue = NumberUtil.toDoubleObject(System.getProperty(propertyName), null);
		return propertyValue != null ? propertyValue : defaultValue;
	}
public static Double getDouble ( String propertyName , Double defaultValue ) { Double propertyValue = NumberUtil . toDoubleObject ( System . getProperty ( propertyName ) , null ) ; return propertyValue != null ? propertyValue : defaultValue ; }
读取Double类型的系统变量，为空时返回默认值.