Struts2迭代器标记 - 从对象列表中访问特定对象值 [英] Struts2 iterator tag - access specific object value from list of objects

问题描述

有没有办法从对象列表中访问特定对象的属性。

Is there a way to access an attribute of specific object from list of objects.

我有一个实验室列表，每个Lab对象都有多个属性。使用标签，我们可以从实验室列表中访问Lab1对象的attribute1的值吗？

I've a List of Labs and each Lab object has multiple attributes. Using tag, can we access value of attribute1 of Lab1 object from the list of labs?

让我们说：我的一个 Lab object有一个名为 labname 的属性，其值为BP，而另一个实验对象的 labname 为A1c 。

现在，如果我想使用 labname 访问lab对象的 labvalue 属性BP我该如何实现呢？

Let's say: one of my Lab object has an attribute called labname with value "BP" and another lab object has labname of "A1c".
Now, if I want to access the labvalue attribute of lab object with labname as "BP" how do I achieve it?

推荐答案

如果您不想使用地图，这更容易，然后你可以利用 OGNL的列表选择功能：

If you don't want to use a Map, that's easier, then you can exploit the OGNL's List Selection feature:

从合集中选择

OGNL提供了一种使用表达式从集合中选择一些
元素的简单方法，并将结果保存在新集合中。
我们从数据库术语中称之为选择，用于从表中选择子行
。例如，这个表达式：

OGNL provides a simple way to use an expression to choose some elements from a collection and save the results in a new collection. We call this "selection," from the database term for choosing a subset of rows from a table. For example, this expression:

listeners.{? #this instanceof ActionListener}

返回所有那些作为
实例的侦听器的列表ActionListener类。

returns a list of all those listeners that are instances of the ActionListener class.

[...]

然后在案例中你描述过，如果你只想过滤 labname 属性等于BP的列表元素，它将是：

Then in the case you described, if you want to filter only the element of the list with the labname attribute equals to "BP" it would be:

<span>
    labvalue attribute for the (first, if any) laboratory with labname="BP" is : 
    <s:property value="labsList.{^ #this.labname == 'BP' }[0].labvalue" />
</span>

根本不需要迭代器。

您还可以迭代投影 / 选择的列表，顺便说一句;）

You can also iterate a projected / selected list, btw ;)

<span>
    All labvalue attributes for all the laboratories with labname="BP" are : 
    <s:iterator value="labsList.{? #this.labname == 'BP' }" >
        <s:property value="labvalue" />
    </s:iterator>
</span>

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