Use of XPath in Java: Part 1

XPath is a query language for traversinig through XML files. It is a syntax for defining parts of XML documents. It uses a path expression to navigate through XML documents.

Xpath expressions are of great help when we want to operate on some specific node in an XML document. I will be creating a XML file and then will create a Java class to read that file and use XPath expressions to navigate through elements in XML. The following procedure will help you in performing some operations.

1. I have created a XML file named file.xml and placed it in my E drive. The File.xml content is:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   <Technologies>
      <Node0>.Net
         <Node1>Abstract
         <Node2>Class
         <Node3>Oops</Node3></Node2></Node1>
         <Node1>CLR</Node1>
      </Node0>
      <Node0> Java</Node0>
      <Node0>PHP</Node0>
      <Node0>C#</Node0>
   </Technologies>

2. Now we will create a Java class file to read this XML file and then do various XPath operations on this file. The code to read the XML file is:

File f = new File("E:\\file.xml");
Document doc =null;
DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance(); DocumentBuilder docBuilder;
docBuilder = docFactory.newDocumentBuilder();
doc = docBuilder.parse(f);
doc.getDocumentElement().normalize();

3. Now we will create an instance of XPath and then will use expressions to navigate through the XML.

XPath xpath = XPathFactory.newInstance().newXPath();

1. The following is an Expression to get the root element of the XML file.
   

   NodeList name = (NodeList)xpath.compile("/*").evaluate(doc, XPathConstants.NODESET);

   This expression will return a NodeList and we get the element name of the root node using a for loop. The code is as follows:
   

   for(int i=0;i<name.getLength();i++)
   {
      System.out.println(name.item(i).getNodeName());
   }

   The output after the running this code is:
   
   Technologies
   
   
2. The following is an Expression to get the text of all Node0 elements.
   

   NodeList name = (NodeList)xpath.compile("//Node0/text()").evaluate(doc, XPathConstants.NODESET);

   This expression will return a NodeList and we can get the text content of all the nodes using a for loop. The code is as follows.
   

   for(int i=0;i<name.getLength();i++)
   {
      System.out.println(name.item(i).getTextContent());
   }

   The output after the running this code is:
   
   .Net
   
   Java
   
   PHP
   
   C#
   
   
3. The following is an Expression to get all the child nodes inside a specific node (Node0).
   

   NodeList name = (NodeList)xpath.compile("//Node0/*").evaluate(doc, XPathConstants.NODESET);

   This expression will return a NodeList and we can get the text content of all the nodes using a for loop. The code is as follows:
   

   for(int i=0;i<name.getLength();i++)
   {
   System.out.println(name.item(i).getTextContent());
   }

   The output after running this code is:
   
   Abstract
   Class
   Oops
   CLR
   
   
4. The following is an Expression to get the element names of all the children of a specific node (Node0).
   

   NodeList name = (NodeList)xpath.compile("//Node0/*").evaluate(doc, XPathConstants.NODESET);

   This expression will return a NodeList and we get the element name of the root node using a for loop. The code is as follows:
   

   for(int i=0;i<name.getLength();i++)
   {
      System.out.println(name.item(i).getNodeName());
   }

   The output after the running this code is:
   
   Node1
   Node1

I will be coming up with XPath operators and some more expressions in future articles. I hope this article was useful to you.