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Java DOM4J parser is an API in Java to parse XML documents. It creates DOM4J document from a built-in SAX parser or a DOM parser. After getting the document, we can retrieve the information of elements and attributes using the built-in methods of DOM4J Document and Element interfaces.
In this chapter, we have used getRootElement() to extract root element of the document and the elements() method to get all of its child elements.
Parse XML Using Java DOM4J Parser
Following are the steps used while parsing a document using Java DOM4J Parser −
- Step 1: Creating SAXReader object
- Step 2: Reading the XML file
- Step 3: Parsing the XML
- Step 4: Extracting the root
- Step 5: Retrieving Elements
Step 1: Creating SAXReader object
The SAXReader class is used to create a DOM4J document from an XML file or stream. It has its own built-in SAX parser to parse the file. We create a SAXReader object as follows −
SAXReader reader = new SAXReader();
Step 2: Reading the XML file
To read XML content as a string, we can use StringBuilder class and later convert it into a ByteStream to create XML document. If XML content is available in the form of a file, we can read it using File class of java.io as follows −
File inputFile = new File("src/input.txt");
Step 3: Parsing the XML
To parse the XML file, we have created SAXReader object in step 1. Using the read() method of SAXReader, we create DOM4J document by passing the file we read in step 2 as an argument as follows −
Document document = reader.read(inputFile);
Step 4: Extracting the Root
The root element needs to be extracted from DOM4J document to obtain any information of elements. Using the getRootElement() method of Document interface we obtain the root element as follows −
Element RootElement = document.getRootElement();
Step 5: Retrieving Elements
After we have followed the first four steps, we now have the root element to obtain the information of its child elements. Now, we are going to perform some tasks such as retrieving the root, retrieving attributes and retrieving element text of an XML document with examples.
Retrieving the Root
The getRootElement() method of Document interface returns the root element of the document in the form of an Element object. To get the name of the element, we use getName() method of Element interface. It returns the name of the element in the form of a String.
Example
The studentData.xml file we need to parse is as follows −
<?xml version = "1.0"?>
<class>
<student rollno = "393">
<firstname>dinkar</firstname>
<lastname>kad</lastname>
<nickname>dinkar</nickname>
<marks>85</marks>
</student>
<student rollno = "493">
<firstname>Vaneet</firstname>
<lastname>Gupta</lastname>
<nickname>vinni</nickname>
<marks>95</marks>
</student>
<student rollno = "593">
<firstname>jasvir</firstname>
<lastname>singn</lastname>
<nickname>jazz</nickname>
<marks>90</marks>
</student>
</class>
The RetrieveRoot.java program reads the above studentData.xml file using a SAXReader and obtains a DOM4J document. After getting the document, we use getRootElement() method to extract the root.
import java.io.File;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class RetrieveRoot {
public static void main(String[] args) {
try {
//Creating SAXReader
SAXReader reader = new SAXReader();
//Reading the XML file
File inputFile = new File("studentData.xml");
//Parsing the XML
Document document = reader.read(inputFile);
//Extracting the root
Element RootElement = document.getRootElement();
//Printing the Root Element Name
System.out.println("Root element Name :" + RootElement.getName());
} catch(Exception e) {
e.printStackTrace();
}
}
}
Output
The root element name, ”class” is displayed on the output screen.
Root element Name :class
Retrieving Attributes
The attributeValue() method of Element interface retrieves the value of the specified attribute in the form of a String. If there is no such attribute for that element, it returns null. If there is no value specified for the attribute, it returns an empty string.
Example
The following RetrieveAttributes.java program uses the attributeValue() method and retrieves all the roll numbers of student elements.
import java.io.File;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class RetrieveAttributes {
public static void main(String[] args) {
try {
//Creating SAXReader
SAXReader reader = new SAXReader();
//Reading the XML file
File inputFile = new File("studentData.xml");
//Parsing the XML
Document document = reader.read(inputFile);
//Extracting the root
Element RootElement = document.getRootElement();
//Iterating over the List
List<Element> elements = RootElement.elements();
System.out.println("Student Roll numbers - ");
for (Element ele : elements) {
System.out.println(ele.attributeValue("rollno") );
}
} catch(Exception e) {
e.printStackTrace();
}
}
}
All the student roll numbers are displayed on the output screen.
Output
Student Roll numbers - 393 493 593
Retrieving Element Text
The elements() method of Element interface returns the list of Elements contained in it. The elementText() method of Element interface returns the text content of the element in the form of a string.
import java.io.File;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class DemoParse {
public static void main(String[] args) {
try {
//Creating SAXReader
SAXReader reader = new SAXReader();
//Reading the XML file
File inputFile = new File("studentData.xml");
//Parsing the XML
Document document = reader.read(inputFile);
//Extracting the root
Element RootElement = document.getRootElement();
System.out.println("Root Element: " + RootElement.getName());
List<Element> elements = RootElement.elements();
System.out.println("---------------------------------");
//Iterating over the List
for (Element ele : elements) {
System.out.println("nCurrent Element :"
+ ele.getName());
System.out.println("Student roll no : "
+ ele.attributeValue("rollno") );
System.out.println("First Name : "
+ ele.elementText("firstname"));
System.out.println("Last Name : "
+ ele.elementText("lastname"));
System.out.println("First Name : "
+ ele.elementText("nickname"));
System.out.println("Marks : "
+ ele.elementText("marks"));
}
} catch (DocumentException e) {
e.printStackTrace();
}
}
}
Output
All the information of students is displayed on the output screen.
Root Element: class --------------------------------- Current Element :student Student roll no : 393 First Name : dinkar Last Name : kad First Name : dinkar Marks : 85 Current Element :student Student roll no : 493 First Name : Vaneet Last Name : Gupta First Name : vinni Marks : 95 Current Element :student Student roll no : 593 First Name : jasvir Last Name : singn First Name : jazz Marks : 90
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