如何从动作类中的速度页面获取数据？(How to get data from the velocity page in a action class?)

 如果您知道只有一个p通过测试，我不知道用null值加p加载创建列表的意义。 
 
 你的问题似乎源于想要使用forEach 。 在我看来，你应该几乎总是使用for循环而不是forEach 。 使用简单的for循环，您可以在找到该项目时使用break 。 
 
 详细： 
 
Instance p = null;
for (Instance q : instances) {
    if (q.i == i) {
        p = q;
        break;
    }
}
if (p == null)
    throw new IllegalStateException();   // It wasn't there.
// Do something with p.

If you know that only one p passes the test, I don't know what the point of creating a list with a load of null values plus p is.
 
Your problem seems to stem from wanting to use forEach. In my opinion, you should almost always use a for loop in preference to forEach. With a simple for loop you can just use break when the item is found.
 
In detail:
 
Instance p = null;
for (Instance q : instances) {
    if (q.i == i) {
        p = q;
        break;
    }
}
if (p == null)
    throw new IllegalStateException();   // It wasn't there.
// Do something with p.