如何在Java中使用XPath读取XML-Java 学习之路

242

我想在Java中使用XPath读取XML数据，因此对于我收集的信息，我无法根据我的要求解析XML .

这是我想要做的：

Get XML file from online via its URL, then use XPath to parse it, I want to create two methods in it. One is in which I enter a specific node attribute id, and I get all the child nodes as result, and second is suppose I just want to get a specific child node value only

<?xml version="1.0"?>
<howto>
  <topic name="Java">
      <url>http://www.rgagnonjavahowto.htm</url>
  <car>taxi</car>
  </topic>
  <topic name="PowerBuilder">
       <url>http://www.rgagnon/pbhowto.htm</url>
       <url>http://www.rgagnon/pbhowtonew.htm</url>
  </topic>
  <topic name="Javascript">
        <url>http://www.rgagnon/jshowto.htm</url>
  </topic>
 <topic name="VBScript">
       <url>http://www.rgagnon/vbshowto.htm</url>
 </topic>
 </howto>

在上面的例子中，我想读取所有元素，如果我通过@name搜索，还有一个函数，我只想从@name'Javascript'中获取url只返回一个节点元素 .

7 回答

6
你需要这样的东西：
```
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(<uri_as_string>);
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile(<xpath_expression>);
```
然后调用 expr.evaluate() 传入该代码中定义的文档和您期望的返回类型，并将结果转换为结果的对象类型 .

如果您需要有关特定XPath表达式的帮助，您应该将其作为单独的问题提出（除非这是您首先提出的问题 - 我理解您的问题是如何在Java中使用API） .

编辑:(对评论的回应）：这个XPath表达式将为您提供PowerBuilder下第一个URL元素的文本：
```
/howto/topic[@name='PowerBuilder']/url/text()
```
这将为您提供第二个：
```
/howto/topic[@name='PowerBuilder']/url[2]/text()
```
你得到这个代码：
```
expr.evaluate(doc, XPathConstants.STRING);
```
如果您不知道给定节点中有多少个URL，那么您应该执行以下操作：
```
XPathExpression expr = xpath.compile("/howto/topic[@name='PowerBuilder']/url");
NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
```
然后遍历NodeList .
回复于 2024-04-29T06:03:34+08:00

你可以试试这个 .

XML文档

保存为 employees.xml .

<?xml version="1.0" encoding="UTF-8"?>
<Employees>
    <Employee id="1">
        <age>29</age>
        <name>Pankaj</name>
        <gender>Male</gender>
        <role>Java Developer</role>
    </Employee>
    <Employee id="2">
        <age>35</age>
        <name>Lisa</name>
        <gender>Female</gender>
        <role>CEO</role>
    </Employee>
    <Employee id="3">
        <age>40</age>
        <name>Tom</name>
        <gender>Male</gender>
        <role>Manager</role>
    </Employee>
    <Employee id="4">
        <age>25</age>
        <name>Meghan</name>
        <gender>Female</gender>
        <role>Manager</role>
    </Employee>
</Employees>

Parser类

该课程有以下方法

列出项目
将返回输入ID的Employee Name的方法 .
将返回员工姓名列表的方法，其年龄大于输入年龄 .
将返回女性员工姓名列表的方法 .

源代码

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

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

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;


public class Parser {

    public static void main(String[] args) {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        DocumentBuilder builder;
        Document doc = null;
        try {
            builder = factory.newDocumentBuilder();
            doc = builder.parse("employees.xml");

            // Create XPathFactory object
            XPathFactory xpathFactory = XPathFactory.newInstance();

            // Create XPath object
            XPath xpath = xpathFactory.newXPath();

            String name = getEmployeeNameById(doc, xpath, 4);
            System.out.println("Employee Name with ID 4: " + name);

            List<String> names = getEmployeeNameWithAge(doc, xpath, 30);
            System.out.println("Employees with 'age>30' are:" + Arrays.toString(names.toArray()));

            List<String> femaleEmps = getFemaleEmployeesName(doc, xpath);
            System.out.println("Female Employees names are:" +
                    Arrays.toString(femaleEmps.toArray()));

        } catch (ParserConfigurationException | SAXException | IOException e) {
            e.printStackTrace();
        }

    }


    private static List<String> getFemaleEmployeesName(Document doc, XPath xpath) {
        List<String> list = new ArrayList<>();
        try {
            //create XPathExpression object
            XPathExpression expr =
                xpath.compile("/Employees/Employee[gender='Female']/name/text()");
            //evaluate expression result on XML document
            NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
            for (int i = 0; i < nodes.getLength(); i++)
                list.add(nodes.item(i).getNodeValue());
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
        return list;
    }


    private static List<String> getEmployeeNameWithAge(Document doc, XPath xpath, int age) {
        List<String> list = new ArrayList<>();
        try {
            XPathExpression expr =
                xpath.compile("/Employees/Employee[age>" + age + "]/name/text()");
            NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
            for (int i = 0; i < nodes.getLength(); i++)
                list.add(nodes.item(i).getNodeValue());
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
        return list;
    }


    private static String getEmployeeNameById(Document doc, XPath xpath, int id) {
        String name = null;
        try {
            XPathExpression expr =
                xpath.compile("/Employees/Employee[@id='" + id + "']/name/text()");
            name = (String) expr.evaluate(doc, XPathConstants.STRING);
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }

        return name;
    }

}

回复于 2024-04-29T06:03:34+08:00

367

入门示例：

xml文件：

<inventory>
    <book year="2000">
        <title>Snow Crash</title>
        <author>Neal Stephenson</author>
        <publisher>Spectra</publisher>
        <isbn>0553380958</isbn>
        <price>14.95</price>
    </book>

    <book year="2005">
        <title>Burning Tower</title>
        <author>Larry Niven</author>
        <author>Jerry Pournelle</author>
        <publisher>Pocket</publisher>
        <isbn>0743416910</isbn>
        <price>5.99</price>
    </book>

    <book year="1995">
        <title>Zodiac</title>
        <author>Neal Stephenson</author>
        <publisher>Spectra</publisher>
        <isbn>0553573862</isbn>
        <price>7.50</price>
    </book>

    <!-- more books... -->

</inventory>

Java代码：

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.testng.annotations.DataProvider;
import org.testng.annotations.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;


try {

    DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
    Document doc = docBuilder.parse (new File("c:\\tmp\\my.xml"));

    // normalize text representation
    doc.getDocumentElement().normalize();
    System.out.println ("Root element of the doc is " + doc.getDocumentElement().getNodeName());

    NodeList listOfBooks = doc.getElementsByTagName("book");
    int totalBooks = listOfBooks.getLength();
    System.out.println("Total no of books : " + totalBooks);

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

        Node firstBookNode = listOfBooks.item(i);
        if(firstBookNode.getNodeType() == Node.ELEMENT_NODE) {

            Element firstElement = (Element)firstBookNode;                              
            System.out.println("Year :"+firstElement.getAttribute("year"));

            //-------
            NodeList firstNameList = firstElement.getElementsByTagName("title");
            Element firstNameElement = (Element)firstNameList.item(0);

            NodeList textFNList = firstNameElement.getChildNodes();
            System.out.println("title : " + ((Node)textFNList.item(0)).getNodeValue().trim());
        }
    }//end of for loop with s var
} catch (SAXParseException err) {
    System.out.println ("** Parsing error" + ", line " + err.getLineNumber () + ", uri " + err.getSystemId ());
    System.out.println(" " + err.getMessage ());
} catch (SAXException e) {
    Exception x = e.getException ();
    ((x == null) ? e : x).printStackTrace ();
} catch (Throwable t) {
    t.printStackTrace ();
}

回复于 2024-04-29T06:03:34+08:00

下面是使用vtd-xml处理xpath的示例...对于重型XML处理，它是首屈一指的 . 这是最近关于这个主题的论文Processing XML with Java – A Performance Benchmark

import com.ximpleware.*;

public class changeAttrVal {
    public  static  void main(String s[]) throws VTDException,java.io.UnsupportedEncodingException,java.io.IOException{
        VTDGen vg = new VTDGen();
        if (!vg.parseFile("input.xml", false))
            return;
        VTDNav vn = vg.getNav();
        AutoPilot ap = new AutoPilot(vn);
        XMLModifier xm = new XMLModifier(vn);
        ap.selectXPath("/*/place[@id=\"p14\" and   @initialMarking=\"2\"]/@initialMarking");
        int i=0;
        while((i=ap.evalXPath())!=-1){
            xm.updateToken(i+1, "499");// change initial marking from 2 to 499
        }
        xm.output("new.xml");
    }

}

回复于 2024-04-29T06:03:34+08:00

扩展@bluish和@Yishai的优秀答案，以下是如何使NodeLists和节点属性支持迭代器，即 for(Node n: nodelist) 接口 .

使用它像：

NodeList nl = ...
for(Node n : XmlUtil.asList(nl))
{...}

和

Node n = ...
for(Node attr : XmlUtil.asList(n.getAttributes())
{...}

代码：

/**
 * Converts NodeList to an iterable construct.
 * From: https://stackoverflow.com/a/19591302/779521
 */
public final class XmlUtil {
    private XmlUtil() {}

    public static List<Node> asList(NodeList n) {
        return n.getLength() == 0 ? Collections.<Node>emptyList() : new NodeListWrapper(n);
    }

    static final class NodeListWrapper extends AbstractList<Node> implements RandomAccess {
        private final NodeList list;

        NodeListWrapper(NodeList l) {
            this.list = l;
        }

        public Node get(int index) {
            return this.list.item(index);
        }

        public int size() {
            return this.list.getLength();
        }
    }

    public static List<Node> asList(NamedNodeMap n) {
        return n.getLength() == 0 ? Collections.<Node>emptyList() : new NodeMapWrapper(n);
    }

    static final class NodeMapWrapper extends AbstractList<Node> implements RandomAccess {
        private final NamedNodeMap list;

        NodeMapWrapper(NamedNodeMap l) {
            this.list = l;
        }

        public Node get(int index) {
            return this.list.item(index);
        }

        public int size() {
            return this.list.getLength();
        }
    }
}

回复于 2024-04-29T06:03:34+08:00

使用XPathFactory，SAXParserFactory和StAX (JSR-173)读取XML文件 .

使用XPath获取节点及其子数据 .

public static void main(String[] args) {
    String xml = "<soapenv:Body xmlns:soapenv='http://schemas.xmlsoap.org/soap/envelope/'>"
            + "<Yash:Data xmlns:Yash='http://Yash.stackoverflow.com/Services/Yash'>"
            + "<Yash:Tags>Java</Yash:Tags><Yash:Tags>Javascript</Yash:Tags><Yash:Tags>Selenium</Yash:Tags>"
            + "<Yash:Top>javascript</Yash:Top><Yash:User>Yash-777</Yash:User>"
            + "</Yash:Data></soapenv:Body>";
    String jsonNameSpaces = "{'soapenv':'http://schemas.xmlsoap.org/soap/envelope/',"
            + "'Yash':'http://Yash.stackoverflow.com/Services/Yash'}";
    String xpathExpression = "//Yash:Data";

    Document doc1 = getDocument(false, "fileName", xml);
    getNodesFromXpath(doc1, xpathExpression, jsonNameSpaces);
    System.out.println("\n===== ***** =====");
    Document doc2 = getDocument(true, "./books.xml", xml);
    getNodesFromXpath(doc2, "//person", "{}");
}
static Document getDocument( boolean isFileName, String fileName, String xml ) {
    Document doc = null;
    try {

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setValidating(false);
        factory.setNamespaceAware(true);
        factory.setIgnoringComments(true);
        factory.setIgnoringElementContentWhitespace(true);

        DocumentBuilder builder = factory.newDocumentBuilder();
        if( isFileName ) {
            File file = new File( fileName );
            FileInputStream stream = new FileInputStream( file );
            doc = builder.parse( stream );
        } else {
            doc = builder.parse( string2Source( xml ) );
        }
    } catch (SAXException | IOException e) {
        e.printStackTrace();
    } catch (ParserConfigurationException e) {
        e.printStackTrace();
    }
    return doc;
}

/**
 * ELEMENT_NODE[1],ATTRIBUTE_NODE[2],TEXT_NODE[3],CDATA_SECTION_NODE[4],
 * ENTITY_REFERENCE_NODE[5],ENTITY_NODE[6],PROCESSING_INSTRUCTION_NODE[7],
 * COMMENT_NODE[8],DOCUMENT_NODE[9],DOCUMENT_TYPE_NODE[10],DOCUMENT_FRAGMENT_NODE[11],NOTATION_NODE[12]
 */
public static void getNodesFromXpath( Document doc, String xpathExpression, String jsonNameSpaces ) {
    try {
        XPathFactory xpf = XPathFactory.newInstance();
        XPath xpath = xpf.newXPath();

        JSONObject namespaces = getJSONObjectNameSpaces(jsonNameSpaces);
        if ( namespaces.size() > 0 ) {
            NamespaceContextImpl nsContext = new NamespaceContextImpl();

            Iterator<?> key = namespaces.keySet().iterator();
            while (key.hasNext()) { // Apache WebServices Common Utilities
                String pPrefix = key.next().toString();
                String pURI = namespaces.get(pPrefix).toString();
                nsContext.startPrefixMapping(pPrefix, pURI);
            }
            xpath.setNamespaceContext(nsContext );
        }

        XPathExpression compile = xpath.compile(xpathExpression);
        NodeList nodeList = (NodeList) compile.evaluate(doc, XPathConstants.NODESET);
        displayNodeList(nodeList);
    } catch (XPathExpressionException e) {
        e.printStackTrace();
    }
}

static void displayNodeList( NodeList nodeList ) {
    for (int i = 0; i < nodeList.getLength(); i++) {
        Node node = nodeList.item(i);
        String NodeName = node.getNodeName();

        NodeList childNodes = node.getChildNodes();
        if ( childNodes.getLength() > 1 ) {
            for (int j = 0; j < childNodes.getLength(); j++) {

                Node child = childNodes.item(j);
                short nodeType = child.getNodeType();
                if ( nodeType == 1 ) {
                    System.out.format( "\n\t Node Name:[%s], Text[%s] ", child.getNodeName(), child.getTextContent() );
                }
            }
        } else {
            System.out.format( "\n Node Name:[%s], Text[%s] ", NodeName, node.getTextContent() );
        }

    }
}
static InputSource string2Source( String str ) {
    InputSource inputSource = new InputSource( new StringReader( str ) );
    return inputSource;
}
static JSONObject getJSONObjectNameSpaces( String jsonNameSpaces ) {
    if(jsonNameSpaces.indexOf("'") > -1)    jsonNameSpaces = jsonNameSpaces.replace("'", "\"");
    JSONParser parser = new JSONParser();
    JSONObject namespaces = null;
    try {
        namespaces = (JSONObject) parser.parse(jsonNameSpaces);
    } catch (ParseException e) {
        e.printStackTrace();
    }
    return namespaces;
}

XML文档

<?xml version="1.0" encoding="UTF-8"?>
<book>
<person>
  <first>Yash</first>
  <last>M</last>
  <age>22</age>
</person>
<person>
  <first>Bill</first>
  <last>Gates</last>
  <age>46</age>
</person>
<person>
  <first>Steve</first>
  <last>Jobs</last>
  <age>40</age>
</person>
</book>

输出给定的XPathExpression：

String xpathExpression = "//person/first";
/*OutPut:
 Node Name:[first], Text[Yash] 
 Node Name:[first], Text[Bill] 
 Node Name:[first], Text[Steve] */

String xpathExpression = "//person";
/*OutPut:
     Node Name:[first], Text[Yash] 
     Node Name:[last], Text[M] 
     Node Name:[age], Text[22] 
     Node Name:[first], Text[Bill] 
     Node Name:[last], Text[Gates] 
     Node Name:[age], Text[46] 
     Node Name:[first], Text[Steve] 
     Node Name:[last], Text[Jobs] 
     Node Name:[age], Text[40] */

String xpathExpression = "//Yash:Data";
/*OutPut:
     Node Name:[Yash:Tags], Text[Java] 
     Node Name:[Yash:Tags], Text[Javascript] 
     Node Name:[Yash:Tags], Text[Selenium] 
     Node Name:[Yash:Top], Text[javascript] 
     Node Name:[Yash:User], Text[Yash-777] */

See this link为我们自己实施 NamespaceContext

回复于 2024-04-29T06:03:34+08:00

这告诉你如何

将XML文件读入 DOM
使用 XPath 筛选出一组 Nodes
对每个提取的 Nodes 执行特定操作 .

我们将使用以下语句调用代码

processFilteredXml(xmlIn, xpathExpr,(node) -> {/*Do something...*/;});

在我们的例子中，我们希望使用 "//book/creators/creator/creatorName" 作为xpath从 book.xml 打印一些 creatorNames ，以在与 XPath 匹配的每个节点上执行 printNode 操作 .

Full code

@Test
public void printXml() {
    try (InputStream in = readFile("book.xml")) {
        processFilteredXml(in, "//book/creators/creator/creatorName", (node) -> {
            printNode(node, System.out);
        });
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private InputStream readFile(String yourSampleFile) {
    return Thread.currentThread().getContextClassLoader().getResourceAsStream(yourSampleFile);
}

private void processFilteredXml(InputStream in, String xpath, Consumer<Node> process) {
    Document doc = readXml(in);
    NodeList list = filterNodesByXPath(doc, xpath);
    for (int i = 0; i < list.getLength(); i++) {
        Node node = list.item(i);
        process.accept(node);
    }
}

public Document readXml(InputStream xmlin) {
    try {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        return db.parse(xmlin);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private NodeList filterNodesByXPath(Document doc, String xpathExpr) {
    try {
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xpath = xPathFactory.newXPath();
        XPathExpression expr = xpath.compile(xpathExpr);
        Object eval = expr.evaluate(doc, XPathConstants.NODESET);
        return (NodeList) eval;
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private void printNode(Node node, PrintStream out) {
    try {
        Transformer transformer = TransformerFactory.newInstance().newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
        StreamResult result = new StreamResult(new StringWriter());
        DOMSource source = new DOMSource(node);
        transformer.transform(source, result);
        String xmlString = result.getWriter().toString();
        out.println(xmlString);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

Prints

<creatorName>Fosmire, Michael</creatorName>

<creatorName>Wertz, Ruth</creatorName>

<creatorName>Purzer, Senay</creatorName>

对于 book.xml

<book>
  <creators>
    <creator>
      <creatorName>Fosmire, Michael</creatorName>
      <givenName>Michael</givenName>
      <familyName>Fosmire</familyName>
    </creator>
    <creator>
      <creatorName>Wertz, Ruth</creatorName>
      <givenName>Ruth</givenName>
      <familyName>Wertz</familyName>
    </creator>
    <creator>
      <creatorName>Purzer, Senay</creatorName>
       <givenName>Senay</givenName>
       <familyName>Purzer</familyName>
    </creator>
  </creators>
  <titles>
    <title>Critical Engineering Literacy Test (CELT)</title>
  </titles>
</book>

回复于 2024-04-29T06:03:34+08:00

如何在Java中使用XPath读取XML

7 回答

XML文档

Parser类

源代码

相关问题