JAXB: Marshalling and Unmarshalling list of objects

Project Description

In this JAXB example we will see how to marshall and unmarshall list of objects.

Environment Used:

JDK 6.
Eclipse Indigo IDE for Java EE Developers.

New project in Eclipse

Create a new Java project in Eclipse IDE and name it as “JAXBList“.

Create Bean class

Create a new Class “Book.java” in the package “com.theopentutorials.jaxb.to” and copy the following code.

package com.theopentutorials.jaxb.to;

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

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "book")
public class Book {
	private String name;
	private String author;
	private String publisher;
	private String isbn;
	
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}

	public String getPublisher() {
		return publisher;
	}

	public void setPublisher(String publisher) {
		this.publisher = publisher;
	}

	public String getIsbn() {
		return isbn;
	}

	public void setIsbn(String isbn) {
		this.isbn = isbn;
	}

	@Override
	public String toString() {
		return "Book [name=" + name + ", author=" + author + ", publisher="
				+ publisher + ", isbn=" + isbn 	+ "]";
	}	
}

This is a simple bean class containing JAXB annotations whose objects are marshalled and unmarshalled. When a top level class is annotated with @XmlRootElement annotation, then its value is represented as XML element, in our case <book> tag.

@XmlAccessorType annotation allows us to configure the use of fields or properties to access the data in our domain object (Book object). This is specified as an XmlAccessType (PUBLIC_MEMBER, PROPERTY, FIELD, or NONE) via the @XmlAccessorType annotation. We use access type FIELD to cause JAXB implementations to create bindings for fields and annotated properties. So in our case all fields – name, author, publisher, isbn are marshalled/unmarshalled by JAXB.

Create Bean class to hold list of objects

Now we need to a new Class “Books.java” in the package “com.theopentutorials.jaxb.to” to hold the list of Book objects by having an ArrayList instance variable in our class.

package com.theopentutorials.jaxb.to;

import java.util.ArrayList;
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.XmlRootElement;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "books")
public class Books {

	@XmlElement(name = "book", type = Book.class)
	private List<Book> books = new ArrayList<Book>();
	
	public Books() {}

	public Books(List<Book> books) {
		this.books = books;
	}

	public List<Book> getBooks() {
		return books;
	}

	public void setBooks(List<Book> books) {
		this.books = books;
	}	
}

This class is a simple holder of list of book objects. We will use this class to marshal and unmarshal list of objects.

Create JAXB Handler (Helper class)

Create a new Class “JAXBXMLHandler.java” in the package “com.theopentutorials.jaxb.xml” and copy the following code.

package com.theopentutorials.jaxb.xml;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.List;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import com.theopentutorials.jaxb.to.Book;
import com.theopentutorials.jaxb.to.Books;

public class JAXBXMLHandler {

	// Export
	public static void marshal(List<Book> books, File selectedFile)
			throws IOException, JAXBException {
		JAXBContext context;
		BufferedWriter writer = null;
		writer = new BufferedWriter(new FileWriter(selectedFile));
		context = JAXBContext.newInstance(Books.class);
		Marshaller m = context.createMarshaller();
		m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
		m.marshal(new Books(books), writer);
		writer.close();
	}

	// Import
	public static List<Book> unmarshal(File importFile) throws JAXBException {
		Books books = new Books();

		JAXBContext context = JAXBContext.newInstance(Books.class);
		Unmarshaller um = context.createUnmarshaller();
		books = (Books) um.unmarshal(importFile);

		return books.getBooks();
	}
}

This is a helper class which has methods to perform marshalling and unmarshalling. These methods are called from client code (in this case, main() method).

Create Java Application client (main())

Create a new Class “JAXBDemo.java” in the package “com.theopentutorials.jaxb.main” and copy the following code.

package com.theopentutorials.jaxb.main;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.JAXBException;

import com.theopentutorials.jaxb.to.Book;
import com.theopentutorials.jaxb.xml.JAXBXMLHandler;

public class JAXBDemo {
	public static void main(String[] args) {
		Book book = new Book();
		book.setAuthor("Kathy Sierra");
		book.setName("SCJP");
		book.setPublisher("Tata McGraw Hill");
		book.setIsbn("856-545456736");
		
		Book book1 = new Book();
		book1.setAuthor("Christian Bauer");
		book1.setName("Java Persistence with Hibernate");
		book1.setPublisher("Manning");
		book1.setIsbn("978-3832180577");
		
		List<Book> books = new ArrayList<Book>();
		books.add(book);
		books.add(book1);
		//Marshalling: Writing Java objects to XMl file
		try {
			JAXBXMLHandler.marshal(books, new File("books.xml"));
		} catch (IOException e) {
			e.printStackTrace();
		} catch (JAXBException e) {
			e.printStackTrace();
		}
		
		//Unmarshalling: Converting XML content to Java objects
		try {
			books = JAXBXMLHandler.unmarshal(new File("books.xml"));
		} catch (JAXBException e) {
			e.printStackTrace();
		}
		System.out.println(books);
	}
}

This class creates two book objects and stores it in list and calls marshal method from JAXBXMLHandler helper class passing list of objects and the file to write the object.
We call unmarshal method passing the marshalled file name which returns list of book objects.
Finally, printing the list of books (books object, which calls toString() from Book class).

Output

Run the JAXBDemo.java.

[Book [name=SCJP, author=Kathy Sierra, publisher=Tata McGraw Hill, isbn=856-545456736],
Book [name=Java Persistence with Hibernate, author=Christian Bauer, publisher=Manning, isbn=978-3832180577]]

Refresh your project in Project Explorer (press F5 on your project) to see the generated XML file.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<books>
    <book>
        <name>SCJP</name>
        <author>Kathy Sierra</author>
        <publisher>Tata McGraw Hill</publisher>
        <isbn>856-545456736</isbn>
    </book>
    <book>
        <name>Java Persistence with Hibernate</name>
        <author>Christian Bauer</author>
        <publisher>Manning</publisher>
        <isbn>978-3832180577</isbn>
    </book>
</books>