02: JAXB with StAX Tutorial step by step for unmarshalling

Posted on December 1, 2016 by

This tutorial extends JAXB Tutorial for XML processing in Java step by step – unmarshall & marshall

When to use JAXB with StAX?

When you want to process large XML files, reading the whole file into memory can cause “OutOfMemoryError” as discussed in Java String & Array limitations and OutOfMemoryError post.

This approach is also good to process the middle of an XML document.

How to read the “book” author & title one by one?


<?xml version="1.0" encoding="utf-8"?>
<books>
  <header>
    <name>Programming Books</name>
  </header>
  <book>
    <author>John Darcy</author>
    <title>Learning Java</title>
  </book>
  <book>
    <author>Peter Smith</author>
    <title>Learning Scala</title>
  </book>
  <footer>
    <records>2</records>
  </footer>
</books>

<?xml version="1.0" encoding="utf-8"?>

<books>

<name>Programming Books</name>

</header>

<book>

<author>John Darcy</author>

<title>Learning Java</title>

</book>

<book>

<author>Peter Smith</author>

<title>Learning Scala</title>

</book>

</footer>

</books>

JAXB and StAX in action


package com.mytutorial;

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.file.Path;
import java.nio.file.Paths;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;

public class App {
    public static void main(String[] args) throws JAXBException, IOException, XMLStreamException, URISyntaxException {
        // Java 1.6 onwards
        JAXBContext jaxbContext = JAXBContext.newInstance(Books.class);

        // unmarshall: String "source" to Java object
        Unmarshaller um = jaxbContext.createUnmarshaller();

        XMLInputFactory xmlFactory = XMLInputFactory.newInstance();
        XMLStreamReader reader = xmlFactory.createXMLStreamReader(new FileReader(getFile()));

        // interested in "book" elements only. Skip up to first "book"
        while (reader.hasNext() && (!reader.isStartElement() || !reader.getLocalName().equals("book"))) {
            reader.next();
        }

        // read a book at a time
        while (reader.getEventType() == XMLStreamConstants.START_ELEMENT) {
            JAXBElement<Book> boolElement = um.unmarshal(reader, Book.class);
            Book book = boolElement.getValue();
            if (book.getAuthor() != null) {  //skip footer tag
                System.out.println(book.getAuthor() + " wrote " + book.getTitle());
            }

            if (reader.getEventType() == XMLStreamConstants.CHARACTERS) {
                reader.next();
            }
        }

        reader.close();
    }

    /**
     * 
     * @return
     * @throws IOException
     * @throws URISyntaxException
     */
    private static final File getFile() throws IOException, URISyntaxException {
        Path path = Paths.get(ClassLoader.getSystemResource("xml/books.xml").toURI());
        return path.toFile();
    }
}

package com.mytutorial;

import java.io.File;

import java.io.FileReader;

import java.io.IOException;

import java.net.URISyntaxException;

import java.nio.file.Path;

import java.nio.file.Paths;

import javax.xml.bind.JAXBContext;

import javax.xml.bind.JAXBElement;

import javax.xml.bind.JAXBException;

import javax.xml.bind.Unmarshaller;

import javax.xml.stream.XMLInputFactory;

import javax.xml.stream.XMLStreamConstants;

import javax.xml.stream.XMLStreamException;

import javax.xml.stream.XMLStreamReader;

public class App {

public static void main(String[] args) throws JAXBException, IOException, XMLStreamException, URISyntaxException {

// Java 1.6 onwards

JAXBContext jaxbContext = JAXBContext.newInstance(Books.class);

// unmarshall: String "source" to Java object

Unmarshaller um = jaxbContext.createUnmarshaller();

XMLInputFactory xmlFactory = XMLInputFactory.newInstance();

XMLStreamReader reader = xmlFactory.createXMLStreamReader(new FileReader(getFile()));

// interested in "book" elements only. Skip up to first "book"

while (reader.hasNext() && (!reader.isStartElement() || !reader.getLocalName().equals("book"))) {

reader.next();

}

// read a book at a time

while (reader.getEventType() == XMLStreamConstants.START_ELEMENT) {

JAXBElement<Book> boolElement = um.unmarshal(reader, Book.class);

Book book = boolElement.getValue();

if (book.getAuthor() != null) { //skip footer tag

System.out.println(book.getAuthor() + " wrote " + book.getTitle());

}

if (reader.getEventType() == XMLStreamConstants.CHARACTERS) {

reader.next();

}

reader.close();

}

/**

* @return

* @throws IOException

* @throws URISyntaxException

private static final File getFile() throws IOException, URISyntaxException {

Path path = Paths.get(ClassLoader.getSystemResource("xml/books.xml").toURI());

return path.toFile();

}

Output:


John Darcy wrote Learning Java
Peter Smith wrote Learning Scala

John Darcy wrote Learning Java

Peter Smith wrote Learning Scala

(Visited 48 times, 2 visits today)

The contents in this Java-Success are copyrighted and from EmpoweringTech pty ltd. The EmpoweringTech pty ltd has the right to correct or enhance the current content without any prior notice. These are general advice only, and one needs to take his/her own circumstances into consideration. The EmpoweringTech pty ltd will not be held liable for any damages caused or alleged to be caused either directly or indirectly by these materials and resources. Any trademarked names or labels used in this blog remain the property of their respective trademark owners. Links to external sites do not imply endorsement of the linked-to sites. Privacy Policy

Responsive WordPress Theme powered by CyberChimps

Top

02: JAXB with StAX Tutorial step by step for unmarshalling

When to use JAXB with StAX?

How to read the “book” author & title one by one?

JAXB and StAX in action

800+ Java & Big Data Interview Q&As

200+ Java & Big Data Tutorials

Disclaimer