JAXB Annotations

Learn about JAXB annotations in detail along with their usage during marshalling and unmarshalling operations.

1) JAXB Annotation Types

Read More : Convert Java Object to XML

1.1) @XmlRootElement

This maps a class or an enum type to an XML root element. When a top-level class or an enum type is annotated with the @XmlRootElement annotation, then its value is represented as XML element in an XML document.

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

Above will result into:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<employee>
	//....
</employee>

1.2) @XmlAccessorType

It defines the fields or properties of your Java classes that the JAXB engine uses for including into generated XML. It has four possible values.

• FIELD – Every non static, non transient field in a JAXB-bound class will be automatically bound to XML, unless annotated by XmlTransient.
• NONE – None of the fields or properties is bound to XML unless they are specifically annotated with some of the JAXB annotations.
• PROPERTY – Every getter/setter pair in a JAXB-bound class will be automatically bound to XML, unless annotated by XmlTransient.
• PUBLIC_MEMBER – Every public getter/setter pair and every public field will be automatically bound to XML, unless annotated by XmlTransient.
• Default value is PUBLIC_MEMBER.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	private Integer id;
	private String firstName;
	private String lastName;
}

Above will result into:

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

1.3) @XmlAccessorOrder

Controls the ordering of fields and properties in a class. You can have predefined values ALPHABETICAL or UNDEFINED.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	private Integer id;
	private String firstName;
	private String lastName;
	private Department department;
}

Above will result into:

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

1.4) @XmlType

It maps a Java class or enum type to a schema type. It defines the type name, namespace and order of its children. It is used to match the element in the schema to element in the model.

@XmlRootElement(name = "employee")
@XmlType(propOrder={"id", "firstName" , "lastName", "department" })
public class Employee implements Serializable 
{
	private Integer id;
	private String firstName;
	private String lastName;
	private Department department;
}

1.5) @XmlElement

Maps a JavaBean property to an XML element derived from property name.

@XmlRootElement(name = "employee")
public class Employee implements Serializable 
{
	@XmlElement(name=employeeId)
	private Integer id;

	@XmlElement
	private String firstName;

	private String lastName;
	private Department department;
}

Above will result into:

<?xml version="1.0" encoding="UTF-8"?>
<employee>
	<employeeId>1</employeeId>
   	<firstName>Lokesh</firstName>
</employee>

1.6) @XmlAttribute

Maps a JavaBean property to an XML attribute.

@XmlRootElement(name = "employee")
public class Employee implements Serializable 
{
	@XmlAttribute
	private Integer id;

	private String firstName;
	private String lastName;
	private Department department;
}

Above will result into:

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

1.7) @XmlTransient

Prevents the mapping of a JavaBean property/type to XML representation. When placed on a class, it indicates that the class shouldn’t be mapped to XML by itself. Properties on such class will be mapped to XML along with its derived classes as if the class is inlined.

@XmlTransient is mutually exclusive with all other JAXB defined annotations.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	@XmlTransient
	private Integer id;

	private String firstName;
	private String lastName;
	private Department department;
}

Above will result into:

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

1.8) @XmlValue

Enables mapping a class to an XML Schema complex type with a simpleContent or an XML Schema simple type. It’s more related to schema mapping to model mapping.

1.9) @XmlList

Used to map a property to a list simple type. It allows multiple values to be represented as whitespace-separated tokens in a single element.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	private List<String> hobbies;
}

//

<?xml version="1.0" encoding="UTF-8"?>
<employee>
	<hobbies>Swimming</hobbies>
    <hobbies>Playing</hobbies>
    <hobbies>Karate</hobbies>
</employee>

After using @XmlList, observe the output.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	@XmlList 
	private List<String> hobbies;
}

//

<?xml version="1.0" encoding="UTF-8"?>
<employee>
	<hobbies>Swimming Playing Karate</hobbies>
</employee>

]

1.10) @XmlElementWrapper

Generates a wrapper element around XML representation. This is primarily intended to be used to produce a wrapper XML element around collections. So, it must be used with collection property.

@XmlRootElement(name = "employee")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee implements Serializable 
{
	@XmlElementWrapper(name="hobbies")
	@XmlElement(name="hobby")
	private List<String> hobbies;
}

Above will result into:

<?xml version="1.0" encoding="UTF-8"?>
<employee>
	<hobbies>
        <hobby>Swimming</hobby>
        <hobby>Playing</hobby>
        <hobby>Karate</hobby>
    </hobbies>
</employee>

2) JAXB Annotation Example

Learn to apply JAXB annotations on model classes and then marshal the object into the XML file.

package com.howtodoinjava.demo.model;

import java.io.Serializable;
import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

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

	private static final long serialVersionUID = 1L;

	private Integer id;
	private String firstName;
	private String lastName;
	
	private Department department;
	
	@XmlElementWrapper(name="hobbies")
	@XmlElement(name="hobby")
	private List<String> hobbies;

	public Employee() {
		super();
	}

	public Employee(int id, String fName, String lName, Department department) {
		super();
		this.id = id;
		this.firstName = fName;
		this.lastName = lName;
		this.department = department;
	}

	//Setters and Getters
}

package com.howtodoinjava.demo;

import java.io.File;
import java.util.Arrays;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import com.howtodoinjava.demo.model.Department;
import com.howtodoinjava.demo.model.Employee;

public class JaxbExample 
{
	public static void main(String[] args) 
	{
		Employee employee = new Employee(1, "Lokesh", "Gupta", new Department(101, "IT"));

		employee.setHobbies(Arrays.asList("Swimming","Playing", "Karate"));

		jaxbObjectToXML(employee);
	}

	private static void jaxbObjectToXML(Employee employee) 
	{
	    try {
	        JAXBContext jaxbContext = JAXBContext.newInstance(Employee.class);
	        Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

	        jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); // To format XML

	        //Print XML String to Console
	        jaxbMarshaller.marshal(employee, new File("employee.xml"));
	        
	    } catch (JAXBException e) {
	        e.printStackTrace();
	    }
	}
}

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

Drop me your questions in comments section.

Happy Learning !!

Reference: JAXB Annotations Java Doc