Use of XPath in Java: Part 1

Introduction

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 a specific node in an XML document. I will be creating a XML file and then, I 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:

< 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();

The following is an Expression to get the root element of the XML file.
1. NodeList name = (NodeList) xpath.compile("/*").evaluate(doc, XPathConstants.NODESET);

This expression will return a NodeList and we will get the element name of the root node, used for a loop. The code is as follows:
1. for (int i = 0; i < name.getLength(); i++) {
2. System.out.println(name.item(i).getNodeName());
3. }
The output after the running this code is:

Technologies
The following is an Expression to get the text of all Node0 elements.
1. 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 used for a loop. The code is as follows.
1. for (int i = 0; i < name.getLength(); i++) {
2. System.out.println(name.item(i).getTextContent());
3. }
The output after running this code is:

.Net

Java

PHP

C#
The following, is an Expression to get all the child nodes inside of a specific node (Node0).
1. 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:
1. for (int i = 0; i < name.getLength(); i++) {
2. System.out.println(name.item(i).getTextContent());
3. }
The output after running this code is:

Abstract

Class

Oops

CLR
The following is an Expression, to get the element names of all the children, of a specific node (Node0).
1. 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, used for a loop. The code is as follows:
1. for (int i = 0; i < name.getLength(); i++) {
2. System.out.println(name.item(i).getNodeName());
3. }
The output after the running this code is:

Node1

Node1

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