Question

我是XML新手。我想根据请求名称阅读以下XML。请帮助我了解如何在Java中阅读以下XML -

<?xml version="1.0"?>
    <config>
        <Request name="ValidateEmailRequest">
            <requestqueue>emailrequest</requestqueue>
            <responsequeue>emailresponse</responsequeue>
        </Request>
        <Request name="CleanEmail">
            <requestqueue>Cleanrequest</requestqueue>
            <responsequeue>Cleanresponse</responsequeue>
        </Request>
    </config>

Answer 1

如果您的XML是String，那么您可以执行以下操作：

String xml = ""; //Populated XML String....

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.parse(new InputSource(new StringReader(xml)));
Element rootElement = document.getDocumentElement();

如果您的XML位于文件中，则Document document将实例化为：

Document document = builder.parse(new File("file.xml"));

document.getDocumentElement()会返回作为文档文档元素的节点（在您的案例中为<config>）。

获得rootElement后，您可以访问元素的属性（通过调用rootElement.getAttribute()方法）等。有关java的更多方法org.w3c.dom.Element

有关java DocumentBuilder＆amp;的更多信息DocumentBuilderFactory。 请记住，提供的示例创建了一个XML DOM树，因此如果您有一个巨大的XML数据，那么该树可能会非常庞大。

Related question。

更新以下是获取元素<requestqueue>的“值”的示例

protected String getString(String tagName, Element element) {
        NodeList list = element.getElementsByTagName(tagName);
        if (list != null && list.getLength() > 0) {
            NodeList subList = list.item(0).getChildNodes();

            if (subList != null && subList.getLength() > 0) {
                return subList.item(0).getNodeValue();
            }
        }

        return null;
    }

您可以有效地将其称为，

String requestQueueName = getString("requestqueue", element);

Answer 2

如果您只想从XML中获取单个值，则可能需要使用Java的XPath库。有关示例，请参阅我对上一个问题的回答：

How to use XPath on xml docs having default namespace

看起来像是：

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

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

public class Demo {

    public static void main(String[] args) {
        DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
        try {
            DocumentBuilder builder = domFactory.newDocumentBuilder();
            Document dDoc = builder.parse("E:/test.xml");

            XPath xPath = XPathFactory.newInstance().newXPath();
            Node node = (Node) xPath.evaluate("/Request/@name", dDoc, XPathConstants.NODE);
            System.out.println(node.getNodeValue());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Answer 3

如果您只需要从xml中检索一个（第一个）值：

public static String getTagValue(String xml, String tagName){
    return xml.split("<"+tagName+">")[1].split("</"+tagName+">")[0];
}

如果要解析整个xml文档，请使用JSoup：

Document doc = Jsoup.parse(xml, "", Parser.xmlParser());
for (Element e : doc.select("Request")) {
    System.out.println(e);
}

Answer 4

有许多不同的方法可以做到这一点。您可能需要查看XStream或JAXB。有教程和示例。

Answer 5

有两种一般方法可以做到这一点。您将创建该XML文件的域对象模型，请查看this

，第二个选择是使用事件驱动的解析，它是DOM xml表示的替代方法。你可以找到这两种基本技术here的最佳整体比较。当然，有关处理xml的更多信息，例如，如果您获得XML模式定义（XSD），则可以使用JAXB。

Answer 6

如果XML格式正确，则可以将其转换为Document。通过使用XPath，您可以获得XML元素。

String xml = "<stackusers><name>Yash</name><age>30</age></stackusers>";

表单XML字符串创建文档并使用其XML路径查找元素。

Document doc = getDocument(xml, true);

    public static Document getDocument(String xmlData, boolean isXMLData) throws Exception {
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        dbFactory.setNamespaceAware(true);
        dbFactory.setIgnoringComments(true);
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc;
        if (isXMLData) {
            InputSource ips = new org.xml.sax.InputSource(new StringReader(xmlData));
            doc = dBuilder.parse(ips);
        } else {
            doc = dBuilder.parse( new File(xmlData) );
        }
        return doc;
    }

使用 org.apache.xpath.XPathAPI 获取Node或NodeList。

System.out.println("XPathAPI:"+getNodeValue(doc, "/stackusers/age/text()"));

NodeList nodeList = getNodeList(doc, "/stackusers");
System.out.println("XPathAPI NodeList:"+ getXmlContentAsString(nodeList));
System.out.println("XPathAPI NodeList:"+ getXmlContentAsString(nodeList.item(0)));

    public static String getNodeValue(Document doc, String xpathExpression) throws Exception {
        Node node = org.apache.xpath.XPathAPI.selectSingleNode(doc, xpathExpression);
        String nodeValue = node.getNodeValue();
        return nodeValue;
    }
    public static NodeList getNodeList(Document doc, String xpathExpression) throws Exception {
        NodeList result = org.apache.xpath.XPathAPI.selectNodeList(doc, xpathExpression);
        return result;
    }

使用javax.xml.xpath.XPathFactory

System.out.println("javax.xml.xpath.XPathFactory:"+getXPathFactoryValue(doc, "/stackusers/age"));

    static XPath xpath = javax.xml.xpath.XPathFactory.newInstance().newXPath();
    public static String getXPathFactoryValue(Document doc, String xpathExpression) throws XPathExpressionException, TransformerException, IOException {
        Node node = (Node) xpath.evaluate(xpathExpression, doc, XPathConstants.NODE);
        String nodeStr = getXmlContentAsString(node);
        return nodeStr;
    }

使用文档元素。

System.out.println("DocumentElementText:"+getDocumentElementText(doc, "age"));

    public static String getDocumentElementText(Document doc, String elementName) {
        return doc.getElementsByTagName(elementName).item(0).getTextContent();
    }

在两个字符串之间获取值。

String nodeVlaue = org.apache.commons.lang.StringUtils.substringBetween(xml, "<age>", "</age>");
System.out.println("StringUtils.substringBetween():"+nodeVlaue);

完整示例：

public static void main(String[] args) throws Exception {
    String xml = "<stackusers><name>Yash</name><age>30</age></stackusers>";
    Document doc = getDocument(xml, true);
    
    String nodeVlaue = org.apache.commons.lang.StringUtils.substringBetween(xml, "<age>", "</age>");
    System.out.println("StringUtils.substringBetween():"+nodeVlaue);
    
    System.out.println("DocumentElementText:"+getDocumentElementText(doc, "age"));
    System.out.println("javax.xml.xpath.XPathFactory:"+getXPathFactoryValue(doc, "/stackusers/age"));
    
    System.out.println("XPathAPI:"+getNodeValue(doc, "/stackusers/age/text()"));
    NodeList nodeList = getNodeList(doc, "/stackusers");
    System.out.println("XPathAPI NodeList:"+ getXmlContentAsString(nodeList));
    System.out.println("XPathAPI NodeList:"+ getXmlContentAsString(nodeList.item(0)));
}
public static String getXmlContentAsString(Node node) throws TransformerException, IOException {
    StringBuilder stringBuilder = new StringBuilder();
    NodeList childNodes = node.getChildNodes();
    int length = childNodes.getLength();
    for (int i = 0; i < length; i++) {
        stringBuilder.append( toString(childNodes.item(i), true) );
    }
    return stringBuilder.toString();
}

输出：

StringUtils.substringBetween():30
DocumentElementText:30
javax.xml.xpath.XPathFactory:30
XPathAPI:30
XPathAPI NodeList:<stackusers>
   <name>Yash</name>
   <age>30</age>
</stackusers>
XPathAPI NodeList:<name>Yash</name><age>30</age>

Answer 7

以下链接可能会有所帮助

http://labe.felk.cvut.cz/~xfaigl/mep/xml/java-xml.htm

http://developerlife.com/tutorials/?p=25

http://www.java-samples.com/showtutorial.php?tutorialid=152

Answer 8

有各种API可用于通过Java读/写XML文件。我会使用StaX

来引用

这也很有用 - Java XML APIs

Answer 9

由于您使用此配置，最好的选择是apache commons-configuration。对于简单文件，它比“原始”XML解析器更容易使用。

请参阅XML how-to

Answer 10

您可以创建一个扩展org.xml.sax.helpers.DefaultHandler并调用

的类

start_<tag_name>(Attributes attrs);

和

end_<tag_name>();

因为它是：

start_request_queue(attrs);

等

然后扩展该类并实现所需的xml配置文件解析器。例如：

  ...
  public void startElement(String uri, String name, String qname,
                           org.xml.sax.Attributes attrs) 
                  throws org.xml.sax.SAXException {
    Class[] args = new Class[2];
    args[0] = uri.getClass();
    args[1] = org.xml.sax.Attributes.class;
    try {
      String mname = name.replace("-", "");
      java.lang.reflect.Method m = 
            getClass().getDeclaredMethod("start" + mname, args);
      m.invoke(this, new Object[] { uri, (org.xml.sax.Attributes)attrs }); 
    }

    catch (IllegalAccessException e) {
      throw new RuntimeException(e);
    }

    catch (NoSuchMethodException e) {
      throw new RuntimeException(e);    }

    catch (java.lang.reflect.InvocationTargetException e) {
      org.xml.sax.SAXException se = 
            new org.xml.sax.SAXException(e.getTargetException());
      se.setStackTrace(e.getTargetException().getStackTrace());
    }

并在特定的配置解析器中：

   public void start_Request(String uri, org.xml.sax.Attributes attrs) {
     // make sure to read attributes correctly
     System.err.println("Request, name="+ attrs.getValue(0);
   }

如何使用Java检索XML的元素值？

10 个答案: