I want to iterate through xml and trying to extract the specific content from the xml using java. Everywhere I am getting solution using xpath only but xpath works on tags basis but in my case I am not sure which tag will come. Tag name can vary dynamically. Below is the xml:

<Employees>  
    <Employee>
        <id>1</id>  
        <username>user1</username>
    </Employee>

    <Detail>
        <greet>Hi</greet>
    </Detail>

    <Employee>  
        <id>2</id>  
        <username>user2</username>
    </Employee>

    <Note>
        <date>2023-01-20</date>
        <heading>reminder</heading>
    </Note>

    <Detail>
        <greet>Hello</greet>
    </Detail>

    <Employee>
        <id>3</id>  
        <username>user3</username>
    </Employee>
</Employees> 

I want to extract tags after each Employee tag. I don't want to iterate through child tags of an Employee. For example I should get :

<Employee>
    <id>1</id>  
    <username>user1</username>
</Employee>

<Detail>
    <greet>Hi</greet>
</Detail>

and next I should get :

<Employee>  
    <id>2</id>  
    <username>user2</username>
</Employee>

<Note>
    <date>2023-01-20</date>
    <heading>reminder</heading>
</Note>

<Detail>
    <greet>Hello</greet>
</Detail>

and next I should get :

<Employee>
    <id>3</id>  
    <username>user3</username>
</Employee>

Can anyone please help me on this how can I implement like this.

CodePudding user response：

You can use XPath to extract all root node's child elements, then iterate over these elements and use Element.getTagName() to check for Employee elements.

Here is a complete example:

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

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

public class ExtractEmployee {


  private static String xml = "<Employees>  \n"  
    "  <Employee>\n"  
    "    <id>1</id>  \n"  
    "    <username>user1</username>\n"  
    "  </Employee>\n"  
    "  <Detail>\n"  
    "    <greet>Hi</greet>\n"  
    "  </Detail>\n"  
    "  <Employee>  \n"  
    "    <id>2</id>  \n"  
    "    <username>user2</username>\n"  
    "  </Employee>\n"  
    "  <Note>\n"  
    "    <date>2023-01-20</date>\n"  
    "    <heading>reminder</heading>\n"  
    "  </Note>\n"  
    "  <Detail>\n"  
    "    <greet>Hello</greet>\n"  
    "  </Detail>\n"  
    "  <Employee>\n"  
    "    <id>3</id>  \n"  
    "    <username>user3</username>\n"  
    "  </Employee>\n"  
    "</Employees> \n";
  public static void main(String[] args) {
    try {
      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
      DocumentBuilder builder = factory.newDocumentBuilder();
      StringReader reader = new StringReader(xml);
      InputSource source = new InputSource(reader);
      Document document = builder.parse(source);
      XPath xpath = XPathFactory.newInstance().newXPath();
      NodeList list = (NodeList) xpath.evaluate("/Employees/*", document, XPathConstants.NODESET);

      List<List<Element>> result = new ArrayList<>();
      List<Element> current = null;

      for(int i = 0; i < list.getLength(); i  ) {
        Element el = (Element) list.item(i);
        if(el.getTagName().equals("Employee")) {
          if(current != null) {
            result.add(current);
          }
          current = new ArrayList<>();
          current.add(el);
        } else {
          if(current != null) {
            current.add(el);
          }
        }
      }
      if(current != null) {
        result.add(current);
      }

      int partNr = 1;
      for(List<Element> part: result) {
        System.out.println("--------------------------------------------------------------------------------");
        System.out.println(String.format("Part number: %d", partNr  ));
        for(Element el: part) {
          System.out.println(element2String(el));
        }
      }
    } catch (ParserConfigurationException e) {
      e.printStackTrace();
    } catch (SAXException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    } catch (XPathExpressionException e) {
      e.printStackTrace();
    }
  }

  private static String element2String(Element element) {
    String xmlString = null;
    try {
      TransformerFactory tf = TransformerFactory.newInstance();
      Transformer transformer = tf.newTransformer();
      transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
      StringWriter writer = new StringWriter();
      transformer.transform(new DOMSource(element), new StreamResult(writer));
      xmlString = writer.getBuffer().toString();
    }
    catch (TransformerException e) {
      e.printStackTrace();
    }
    catch (Exception e) {
      e.printStackTrace();
    }
    return xmlString;
  }

}

Output is:

--------------------------------------------------------------------------------
Part number: 1
<Employee>
    <id>1</id>  
    <username>user1</username>
  </Employee>
<Detail>
    <greet>Hi</greet>
  </Detail>
--------------------------------------------------------------------------------
Part number: 2
<Employee>  
    <id>2</id>  
    <username>user2</username>
  </Employee>
<Note>
    <date>2023-01-20</date>
    <heading>reminder</heading>
  </Note>
<Detail>
    <greet>Hello</greet>
  </Detail>
--------------------------------------------------------------------------------
Part number: 3
<Employee>
    <id>3</id>  
    <username>user3</username>
  </Employee>