JAVA EE: How to convert an object into XML and XML into an object using JAXB?

Saturday, 14 September 2019

How to convert an object into XML and XML into an object using JAXB? - BookStore Example

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What is JAXB? (Java Architecture for XML Binding)

JAXB stands for Java Architecture for XML Binding. It provides a quick and convenient way to bind XML schemas and Java representations, making it easy for Java developers to read and write XML data without needing low-level XML parsers like DOM or SAX.

Key Concepts: Marshalling & Unmarshalling

Working with JAXB revolves around two fundamental operations:

Marshalling (Object to XML): The process of serializing a Java object tree into an XML document or stream.
Unmarshalling (XML to Object): The process of deserializing XML data back into a structured Java object.

Essential JAXB Annotations

To map your Java classes to XML structures, JAXB uses simple annotations:

@XmlRootElement: Defines the top-level root element of the XML document.
@XmlElement: Maps a Java field or getter/setter to an XML child tag.
@XmlAttribute: Maps a field as an attribute within an XML element.
@XmlElementWrapper: Generates a wrapper XML element around collection elements (such as a list of books).

Step-by-Step BookStore Example

1. Define the Book & BookStore Classes

Create your POJO classes and annotate them so JAXB knows how to convert the properties:

@XmlRootElement(name = "bookstore")
public class BookStore {
    private String name;
    private List<Book> bookList;

    @XmlElement(name = "name")
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    @XmlElementWrapper(name = "bookList")
    @XmlElement(name = "book")
    public List<Book> getBookList() { return bookList; }
    public void setBookList(List<Book> bookList) { this.bookList = bookList; }
}

2. Marshalling: Converting Java Object to XML

JAXBContext context = JAXBContext.newInstance(BookStore.class);
Marshaller marshaller = context.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

// Write to console or file
marshaller.marshal(bookStore, System.out);

3. Unmarshalling: Converting XML to Java Object

JAXBContext context = JAXBContext.newInstance(BookStore.class);
Unmarshaller unmarshaller = context.createUnmarshaller();

BookStore bookStore = (BookStore) unmarshaller.unmarshal(new File("bookstore.xml"));
System.out.println("Store Name: " + bookStore.getName());