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如果java中的XML中不存在节点或子节点，XPath如何返回空字符串

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I have one XML file as "sample.xml" and has 4 records .

<?xml version='1.0' encoding='UTF-8'?>
<hello xmlns:show="http://www.example.com" xmlns:css="http://www.example.com" xml_version="2.0">


  <entry id="2008-0001">
    <show:id>2008-0001</show:id>
    <show:published-datetime>2008-01-15T15:00:00.000-05:00</show:published-datetime>
    <show:last-modified-datetime>2012-03-19T00:00:00.000-04:00</show:last-modified-datetime>
    <show:css>
      <css:metrics>
        <css:score>3.6</css:score>
        <css:access-vector>LOCAL</css:access-vector>
        <css:authentication>NONE</css:authentication>
        <css:generated-on-datetime>2008-01-15T15:22:00.000-05:00</css:generated-on-datetime>
      </css:metrics>
    </show:css>
    <show:summary>This is first entry.</show:summary>
  </entry>
  <entry id="2008-0002">
    <show:id>2008-0002</show:id>
    <show:published-datetime>2008-02-11T20:00:00.000-05:00</show:published-datetime>
    <show:last-modified-datetime>2014-03-15T23:22:37.303-04:00</show:last-modified-datetime>
    <show:css>
      <css:metrics>
        <css:score>5.8</css:score>
        <css:access-vector>NETWORK</css:access-vector>
        <css:authentication>NONE</css:authentication>
        <css:generated-on-datetime>2008-02-12T10:12:00.000-05:00</css:generated-on-datetime>
      </css:metrics>
    </show:css>
    <show:summary>This is second entry.</show:summary>
  </entry>

  <entry id="2008-0003">
    <show:id>2008-0003</show:id>
    <show:published-datetime>2009-03-26T06:12:08.780-04:00</show:published-datetime>
    <show:last-modified-datetime>2009-03-26T06:12:09.313-04:00</show:last-modified-datetime>
    <show:summary>This is 3rd entry with missing "css" tag and their metrics.</show:summary>
  </entry>

  <entry id="2008-0004">
    <show:id>CVE-2008-0004</show:id>
    <show:published-datetime>2008-01-11T19:46:00.000-05:00</show:published-datetime>
    <show:last-modified-datetime>2011-09-06T22:41:45.753-04:00</show:last-modified-datetime>
    <show:css>
      <css:metrics>
        <css:score>4.3</css:score>
        <css:access-vector>NETWORK</css:access-vector>
        <css:authentication>NONE</css:authentication>
        <css:generated-on-datetime>2008-01-14T09:37:00.000-05:00</css:generated-on-datetime>
      </css:metrics>
    </show:css>
    <show:summary>This is 4th entry.</show:summary>
  </entry>
</hello>

and 1 Java file as "Test.java" -

import java.io.File;
    import java.util.ArrayList;
    import java.util.List;

    import javax.xml.parsers.DocumentBuilder;
    import javax.xml.parsers.DocumentBuilderFactory;
    import javax.xml.xpath.XPath;
    import javax.xml.xpath.XPathConstants;
    import javax.xml.xpath.XPathExpression;
    import javax.xml.xpath.XPathFactory;

    import org.w3c.dom.Document;
    import org.w3c.dom.Node;
    import org.w3c.dom.NodeList;

public class Test {

    public static void main(String[] args) {



        List<String> list = new ArrayList<String>();


        File fXmlFile = new File("/home/ankit/sample.xml");

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

        try
        {
            DocumentBuilder dBuilder = factory.newDocumentBuilder();

            Document doc = dBuilder.parse(fXmlFile);

            doc.getDocumentElement().normalize();

            NodeList nList = doc.getElementsByTagName("entry");

            XPathFactory xPathfactory = XPathFactory.newInstance();

            XPath xpath = xPathfactory.newXPath();


            for (int i = 0; i < nList.getLength(); i++)
            {

                XPathExpression expr1 = xpath.compile("//hello/entry/css/metrics/score");

                NodeList nodeList1 = (NodeList) expr1.evaluate(doc, XPathConstants.NODESET);

                if(nodeList1.item(i)!=null)
                {
                    Node currentItem = nodeList1.item(i);

                    if(!currentItem.getTextContent().isEmpty())
                    {
                        list.add(currentItem.getTextContent());
                        }
                }
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

        System.out.println("size----"+list.size());
        for(int i=0;i<list.size();i++)
        {
            System.out.println("list----"+list.get(i));
        }
    }
}

我需要从XML中读取 <entry> 标记，并且我正在使用XPath . 在XML文件中有4个条目标签和内部条目标签有 <show:css> 标签，但是在第3个 <entry> 标签中，这个 <show:css> 标签丢失并且将那些css标签's score values in the list. So when I am running this java code first 2 values got stored in the list and at the 3rd place it stores 4th tag' s css的分数值 .

我想要一个列表作为输出，其中第一个，第二个和第四个元素为“3.6”，“4.8”和“5.3”，第三个元素应为空字符串或nill . 但是我在列表中只获得了3个元素，值为1,2和4 .

I need to put empty string “” at 3rd place and original value at 4th. Means If that tag is not present then put blank value in the list.

Current output - [“3.6” , “4.8” , “5.3”]

I expect - [“3.6” , “4.8” , “” , “5.3”]

任何人都可以帮我解决这个问题 .

java xml xpath

3 回答

  • 0

    可能有几种方法可以实现......

    我的基本观点是找到所有 entry 节点，这些节点有一个 css/metrics/score 子节点，哪些节点没有（你可能只能得到所有的 entry 节点，但这证明了查询语言的强大功能）

    就像是...

    XPathExpression expr1 = xPath.compile("//hello/entry[css/metrics/score or not(css/metrics/score)]");

    我知道条件表达式意义较小，我希望OP看到他们可以使用额外的条件来扩展那些要求，谢谢大家指出尽管事实我已经提到它...希望我们都能动从它

    然后，遍历生成的 NodeList 并查询 css/metrics/score 节点的每个 entry Node . 如果它是 null ，那么将 null 值添加到列表中（或者你想要的任何其他内容），例如......

    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
Document doc = dbf.newDocumentBuilder().parse(JavaApplication908.class.getResourceAsStream("/Hello.xml"));

XPathFactory xf = XPathFactory.newInstance();
XPath xPath = xf.newXPath();

XPathExpression expr1 = xPath.compile("//hello/entry[css/metrics/score or not(css/metrics/score)]");
XPathExpression expr2 = xPath.compile("css/metrics/score");

List<String> values = new ArrayList<>(25);

NodeList nodeList1 = (NodeList) expr1.evaluate(doc, XPathConstants.NODESET);
for (int index = 0; index < nodeList1.getLength(); index++) {
    Node node = nodeList1.item(index);
    System.out.println(node.getAttributes().getNamedItem("id"));

    Node css = (Node) expr2.evaluate(node, XPathConstants.NODE);
    if (css != null) {
        values.add(css.getTextContent());
    } else {
        values.add(null);
    }

}

for (String value : values) {
    System.out.println(value);
}

    这输出......

    id="2008-0001"
id="2008-0002"
id="2008-0003"
id="2008-0004"
3.6
5.8
null
4.3

    （前四行是 entry 节点 id s，后四行是生成的 css/metrics/score 值）

    回复于
  • 0

    我不是XPath的专家，但从查看你的代码，我认为你只是缺少几行代码，

    if(nodeList1.item(i)!=null)
{
   Node currentItem = nodeList1.item(i);
   if(!currentItem.getTextContent().isEmpty())
   {
     list.add(currentItem.getTextContent());
   }
   else
     list.add("");
}
else
 list.add("");
    回复于
  • 1

    @MathiasMüller你可以告诉我如何在XPath 2.0中的1表达式中完成它 . - ankit

    等效的XPath 2.0表达式

    for $x in //entry return (if ($x//*:score) then $x//*:score else '')

    这大量使用了XPath 2.0中引入的新构造 . 那么输出就是

    3.6
5.8
[Empty string]
4.3

    但请注意，目前大多数XPath实现仅支持1.0 . 在使用Saxon 9.5 EE的XSLT样式表online here中尝试此XPath 2.0表达式 .

    回复于

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