JAXB Unmarshaller Example

The JAXB Unmarshaller interface is responsible for governing the process of deserializing the XML data to Java Objects. The unmarshalling to objects can be done to variety of input sources.

1. How to unmarshal XML to Object

1.1. Create Unmarshaller

Generally, to create Unmarshaller you can reuse this code.

JAXBContext jaxbContext 	= JAXBContext.newInstance( Employee.class );
Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

//Overloaded methods to unmarshal from different xml sources
Employee employee = (Employee) jaxbUnmarshaller.unmarshal( xmlSource );

1.2. Unmarshalling from an InputStream

InputStream inStream = new FileInputStream( "employee.xml" );

Employee employee = (Employee) jaxbUnmarshaller.unmarshal( inStream );

1.3. Unmarshalling from a URL

URL url = new URL( "http://localhost:8080/employee.xml" );

Employee employee = (Employee) jaxbUnmarshaller.unmarshal( url );

1.4. Unmarshalling the String content

String xmlString = "...";

Employee employee = (Employee) jaxbUnmarshaller.unmarshal(new StringReader(xmlString));

1.5. Unmarshalling from a org.w3c.dom.Node

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
DocumentBuilder db = dbf.newDocumentBuilder();
Document document = db.parse(new File( "employee.xml")); //Node

Employee employee = (Employee) jaxbUnmarshaller.unmarshal( document );

2. JAXB Unmarshaller Properties

There currently are not any properties required to be supported by all JAXB Providers on Unmarshaller. However, some providers may support their own set of provider specific properties.

3. Unmarshaller Event Callbacks

You can customize the Unmarshalling operation by adding these callback methods inside JAXB annotated class e.g. Employee.java. You need to define two methods which will listen before and after the Unmarshaller process that class.

  • void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {}
  • void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {}
package com.howtodoinjava.demo.model;

import java.io.Serializable;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Employee implements Serializable {

	private static final long serialVersionUID = 1L;

	private Integer id;
	private String firstName;
	private String lastName;
	private Department department;

	public Employee() {
		super();
	}

	//Setters and Getters

	@Override
	public String toString() {
		return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", department="
				+ department + "]";
	}

	// It is called immediately after the object is created and before the unmarshalling begins.
	// The callback provides an opportunity to initialize JavaBean properties prior to unmarshalling.
	void beforeUnmarshal(Unmarshaller unmarshaller, Object parent) {
		System.out.println("Before Unmarshaller Callback");
	}

	// It is called after all the properties are unmarshalled for this object,
	// but before this object is set to the parent object.
	void afterUnmarshal(Unmarshaller unmarshaller, Object parent) {
		System.out.println("After Unmarshaller Callback");
	}
}

4. JAXB Unmarshaller Example

Example of unmarshalling XML file to Java Object.

package com.howtodoinjava.demo;

import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import com.howtodoinjava.demo.model.Employee;

public class JaxbExample 
{
	public static void main(String[] args) 
	{
		String fileName = "employee.xml";

		jaxbXmlFileToObject(fileName);
	}

	private static void jaxbXmlFileToObject(String fileName) {
		
		File xmlFile = new File(fileName);
		
		JAXBContext jaxbContext;
		try 
		{
			jaxbContext = JAXBContext.newInstance(Employee.class);
			Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
			
			Employee employee = (Employee) jaxbUnmarshaller.unmarshal(xmlFile);
			
			System.out.println(employee);
		}
		catch (JAXBException e) 
		{
			e.printStackTrace();
		}
	}
}

Program Output.

Before Unmarshaller Callback
After Unmarshaller Callback

Employee [id=1, firstName=Lokesh, lastName=Gupta, department=Department [id=101, name=IT]]

Where employee.xml file is:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<employee>
    <department>
        <id>101</id>
        <name>IT</name>
    </department>
    <firstName>Lokesh</firstName>
    <id>1</id>
    <lastName>Gupta</lastName>
</employee>

Drop me your questions in comments section related to unmarshalling in java using jaxb.

Happy Learning !!

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