我想读入一个 XML 文件并在特定元素中放置一个递增的 id。这是我编写的一些测试代码，用于弄清楚如何做到这一点：
import scala.xml._
import scala.xml.transform._
val testXML =
<document>
<authors>
<author>
<first-name>Firstname</first-name>
<last-name>Lastname</last-name>
</author>
</authors>
</document>
def addIDs(node : Node) : Node = {
object addIDs extends RewriteRule {
var authorID = -1
var emailID = -1
var instID = -1
override def transform(elem: Node): Seq[Node] =
{
elem match {
case Elem(prefix, "author", attribs, scope, _*) =>
//println("element author: " + elem.text)
if ((elem \ "@id").isEmpty) {
println("element id is empty:" + elem\"@id")
authorID += 1
println("authorID is " + authorID)
elem.asInstanceOf[Elem] % Attribute(None, "id", Text(authorID.toString), Null)
} else {
elem
}
case Elem(prefix, "email", attribs, scope, _*) =>
println("EMAIL")
elem.asInstanceOf[Elem] % Attribute(None, "id", Text(authorID.toString), Null)
case Elem(prefix, "institution", attribs, scope, _*) =>
println("INST")
elem.asInstanceOf[Elem] % Attribute(None, "id", Text(instID.toString), Null)
case other =>
other
}
}
}
object transform extends RuleTransformer(addIDs)
transform(node)
}
val newXML = addIDs(testXML)
此代码是功能性的 - 但是，id 没有按预期出现：
element id is empty:
authorID is 0
element id is empty:
authorID is 1
element id is empty:
authorID is 2
element id is empty:
authorID is 3
element id is empty:
authorID is 4
element id is empty:
authorID is 5
element id is empty:
authorID is 6
element id is empty:
authorID is 7
newXML:scala.xml.Node=<document>
<authors>
<author id="7">
<first-name>Firstname</first-name>
<last-name>Lastname</last-name>
</author>
</authors>
</document>
看起来变压器多次撞击每个节点，增加 id，然后当 id 达到 7 时最终停止。为什么它在最终完成之前接触节点这么多次？有什么我可以做不同的事情来告诉它完成那个节点吗？
我想也许它正在遍历新修改的节点，因此我检查了包含名为“id”的属性的元素。但这似乎不起作用。也许一开始就这样做是个坏主意？
感谢您对此的任何帮助。