Marshalling: How to Convert Java Objects to XML Using JAXB

Marshalling is the process of converting a Java object into XML format, making it easier to store or share data in a platform-independent manner. JAXB (Java Architecture for XML Binding) is a popular framework in Java for handling XML and binding it to Java objects. It simplifies the task of mapping Java classes to XML representations and vice versa.

In this post, we'll walk through the process of converting Java objects to XML using JAXB.

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What Is JAXB?

JAXB is a part of the Java Standard Edition and provides a standard way to map Java objects to XML and back. It uses annotations to define the relationship between Java classes and XML elements, making it easy to serialize objects into XML or deserialize XML into objects.

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Key Steps in Marshalling Using JAXB

Here's a step-by-step guide to converting a Java object into XML:

1. Add JAXB Dependency

If you are using Java 9 or above, JAXB is no longer included in the JDK. Add the following 

Maven dependency to your pom.xml file:

<dependency>

    <groupId>javax.xml.bind</groupId>

    <artifactId>jaxb-api</artifactId>

    <version>2.3.1</version>

</dependency>

<dependency>

    <groupId>com.sun.xml.bind</groupId>

    <artifactId>jaxb-impl</artifactId>

    <version>2.3.1</version>

</dependency>

2. Create a Java Class

Define the Java class that represents the data you want to convert to XML. Use JAXB annotations to specify how the class maps to XML.

import javax.xml.bind.annotation.XmlElement;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement // Marks this class as the root element of the XML

public class Employee {

    private int id;

    private String name;

    private double salary;

    // Default constructor is required for JAXB

    public Employee() {}

    public Employee(int id, String name, double salary) {

        this.id = id;

        this.name = name;

        this.salary = salary;

    }

    @XmlElement // Maps this field to an XML element

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    @XmlElement

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @XmlElement

    public double getSalary() {

        return salary;

    }

    public void setSalary(double salary) {

        this.salary = salary;

    }

}

3. Perform Marshalling

Write the logic to convert the Employee object into an XML string or file.

import javax.xml.bind.JAXBContext;

import javax.xml.bind.JAXBException;

import javax.xml.bind.Marshaller;

import java.io.File;

public class MarshallingExample {

    public static void main(String[] args) {

        try {

            // Create an Employee object

            Employee employee = new Employee(101, "John Doe", 75000.0);

            // Create a JAXB context for the Employee class

            JAXBContext context = JAXBContext.newInstance(Employee.class);

            // Create a Marshaller

            Marshaller marshaller = context.createMarshaller();

            // Format the XML output for better readability

            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

            // Marshal the object to a file

            marshaller.marshal(employee, new File("employee.xml"));

            // Marshal the object to the console

            marshaller.marshal(employee, System.out);

        } catch (JAXBException e) {

            e.printStackTrace();

        }

    }

}

4. Output XML

Running the above program will generate an XML file (employee.xml) and print the following output to the console:

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

<employee>

    <id>101</id>

    <name>John Doe</name>

    <salary>75000.0</salary>

</employee>

JAXB Annotations Cheat Sheet

Here are some commonly used JAXB annotations:

Annotation	Purpose
@XmlRootElement	Specifies the root element in the XML document.
@XmlElement	Maps a field to an XML element.
@XmlAttribute	Maps a field to an XML attribute.
@XmlType	Defines the order of elements in the XML schema.
@XmlTransient	Excludes a field from the XML output.

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Benefits of Using JAXB

1. Ease of Use: JAXB simplifies XML handling with minimal configuration.
2. Annotation-Based: The annotations are straightforward, reducing the need for external mapping files.
3. Integration: JAXB works seamlessly with Java and is widely supported in various frameworks.