Question

我是Xpath的新手，我正在按照教程在xml文件中搜索一些目标数据，并根据下面发布的xml文件编写了以下代码。并且如下面的发布结果所示，我得到了一个nodeList，其中填充了四个null元素，我希望NodeList可以填充四封电子邮件，因为我的搜索表达式是

String expression1 = "/Employees//Employee[position()<=4]//email";

请让我知道为什么我会得到四个空元素

代码：

public static void main(String[] args) throws FileNotFoundException, SAXException, IOException, XPathExpressionException {

    DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = null;

    try {
        builder = builderFactory.newDocumentBuilder();
    } catch (ParserConfigurationException e) {
        e.printStackTrace();  
    }

    Document document = builder.parse(new FileInputStream("c:\\xml0.xml"));
    XPath xPath =  XPathFactory.newInstance().newXPath();

    String expression1 = "/Employees//Employee[position()<=4]//email";

    String email = xPath.compile(expression1).evaluate(document);
    System.out.println(email);

    Node node = (Node) xPath.compile(expression1).evaluate(document, XPathConstants.NODE);
    NodeList nodeList = (NodeList) xPath.compile(expression1).evaluate(document, XPathConstants.NODESET);

    System.out.println(nodeList.getLength());
    System.out.println(nodeList.item(0));
    System.out.println(nodeList.item(1));
    System.out.println(nodeList.item(2));
    System.out.println(nodeList.item(3));

}

XML ：

<?xml version="1.0"?>

<Employees>
<Employee emplid="1111" type="admin">
    <firstname>John</firstname>
    <lastname>Watson</lastname>
    <age>30</age>
    <email>johnwatson@sh.com</email>
   </Employee>

<Employee emplid="2222" type="admin">
    <firstname>Sherlock</firstname>
    <lastname>Homes</lastname>
    <age>32</age>
    <email>sherlock@sh.com</email>
</Employee>

<Employee emplid="4444" type="user">
    <firstname>Jim</firstname>
    <lastname>Moriarty</lastname>
    <age>52</age>
    <email>jim@sh00.com</email>
</Employee>

<Employee emplid="4444" type="user">
    <firstname>Jim</firstname>
    <lastname>Moriarty</lastname>
    <age>52</age>
    <email>jim@sh33.com</email>
</Employee>

<Employee emplid="5555" type="admin">
    <firstname>Mycroft</firstname>
    <lastname>Holmes</lastname>
    <age>41</age>
    <email>mycroft@sh.com</email>
</Employee>

</Employees>

结果：

johnwatson@sh.com
4
[email: null]
[email: null]
[email: null]
[email: null]

Answer 1

首先，您不需要＆＃34; /员工//员工[position（）＆lt; = 4] //电子邮件＆＃34;在这个XML中。＆＃39; //＆＃39;表示任何后代，但在此XML中，Employee是Employees的直接子项，这意味着简单的＆＃39; /＆＃39;会做的。

要清除输出不为null。输出是节点元素＆＃39;电子邮件＆＃39;，这毕竟是您所要求的。

要获取您需要使用的文本值：＆＃34; /雇员/雇员[位置（）＆LT; = 4] /电子邮件/文本（）＆＃34;

Answer 2

我认为你在表达中错过了/text()。尝试将其更改为

String expression1 = "/Employees//Employee[position()<=5]/email/text()";

否则，代码对我来说很好

搜索表达式返回四个空元素

2 个答案: