java - JDOM2 和 XPath

Question

当我运行以下命令时

XPathFactory xpathFactory = XPathFactory.instance();
XPathExpression<Double> query =
xpathFactory.compile("count(1)", Filters.fdouble());
List<Double> result = query.evaluate(new Element("test"));

但是评估失败:

无法计算表达式。查看原因原因:功能:计数

这是一个有点无意义的例子，但我想要一些独立的东西。这有什么问题吗？

Answer 1

如果您想计算 test 元素的数量，请尝试此操作；

Element root = new Element("test");
Document doc = new Document(root);

XPathFactory xpathFactory = XPathFactory.instance();
XPathExpression<Double> query = xpathFactory.compile("count(//test)", Filters.fdouble());
List<Double> result = query.evaluate(doc);