java JSF - 在单一方法中检查 null 和 empty
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JSF - checking null and empty in single method
提问by Ketan
Currently my code is like
目前我的代码就像
<h:panelGroup rendered="#{templatePrescriptionMaintenanceBackingBean.allSelectedMedicationList != null && !empty templatePrescriptionMaintenanceBackingBean.allSelectedMedicationList}">
<b>List of Selected Drugs</b> // and some other stuff
</h:panelGroup>
Now allSelectedMedicationListwill do lot of process in backend. Calling webservice and adding data in current DB and so on...
现在allSelectedMedicationList将在后端做很多处理。调用 webservice 并在当前数据库中添加数据等等...
Now issue arise when I need to check nullor empty- 2 timesthat method called here. Once again when I use same method with datatable it will call again 1 moretime.
I think to create one method or something for JSF it self that will check nulland emptyat same time and return list. Is it possible?
现在，当我需要检查null或empty-此处调用该方法的2 次时出现问题。再一次，当我对数据表使用相同的方法时，它会再调用1次。我想为 JSF 自己创建一种方法或其他东西，它会检查null并empty同时返回列表。是否可以？
回答by Pablo
The operator "empty" already does what you want, you don't need to also check null.
运算符“空”已经做了你想要的，你不需要也检查空。
From http://docs.oracle.com/javaee/5/tutorial/doc/bnahq.html#bnaik:
来自http://docs.oracle.com/javaee/5/tutorial/doc/bnahq.html#bnaik：
Empty: The empty operator is a prefix operation that can be used to determine whether a value is null or empty.
Empty：空操作符是一个前缀操作，可用于确定一个值是空值还是空值。
