返回空列表的javax.persistence.Query.getResultList（）

Question

I am using getResultList ( List javax.persistence.Query.getResultList() ) in my dao to fetch a list of objects. Any idea why it may return {null,null,null,null,null,null,null,null,null,null} for a query which was has no match in the db. This is causing my code List. hasNext() to break which was working fine earlier. I wasn't working in this project for a while (If it matters). It's using

hibernate-core-4.1.9.Final-sources.jar

I saw this and understands it is returning list now.

• Since which version this change has come to effect?
• How the hibernate decide the size of this list?
• How to stay away from this kind of errors in general?

Answer 1

Just guessing: You checked your list in the debugger and didn't look at the size property? Hibernate returns an ArrayList without an explicit capacity in many cases. And the ArrayList initializes its internal array with 10 null elements then (to avoid creating an array again and again while adding elements). But if you ask list.iterator().hasNext() it should return false (as well as list.isEmpty() returns true and list.size() returns 0 ).

Answer 2

Just add an isEmpty check on the result list:

List<SomeType> resultList = query.getResultList();
if (resultList.isEmpty()){
    //Handle it
}

The result list somehow always contains some nulls, I used the isEmpty check to prevent errors later on.

Answer 3

You could prevent this by checking for null elements in your List.hasNext().

 if(variable = list.next() !=null)  
    // do something

Answer 4

• At least version 3.2.7
• To avoid these kind of crashes, always always verify input. Whether you pull it from forms, databases, files or whatever kind of source. Verify that what you receive is what you expect it to be, otherwise discard/omit it.