Streaming API for XML, called StaX, is an API for reading and writing XML Documents.

StaX is a Pull-Parsing model. Application can take the control over parsing the XML documents by pulling (taking) the events from the parser.

The core StaX API falls into two categories and they are listed below. They are

Applications can any of these two API for parsing XML documents. The following will focus on the event iterator API as I consider it more convenient to use.

The event iterator API has two main interfaces: XMLEventReader for parsing XML and XMLEventWriter for generating XML.

This example is stored in project "de.vogella.xml.stax.reader".

Applications loop over the entire document requesting for the Next Event. The Event Iterator API is implemented on top of Cursor API.

In this example we will read the following XML document and create objects from it. file.

				
<?xml version="1.0" encoding="UTF-8"?>
<config>
	<item date="January 2009">
		<mode>1</mode>
		<unit>900</unit>
		<current>1</current>
		<interactive>1</interactive>
	</item>
	<item date="February 2009">
		<mode>2</mode>
		<unit>400</unit>
		<current>2</current>
		<interactive>5</interactive>
	</item>
	<item date="December 2009">
		<mode>9</mode>
		<unit>5</unit>
		<current>100</current>
		<interactive>3</interactive>
	</item>
</config>

			

Define therefore the following class to store the individual entries of the XML file.

				
package de.vogella.xml.stax.model;

public class Item {
	private String date; 
	private String mode;
	private String unit;
	private String current;
	private String interactive;
	
	public String getDate() {
		return date;
	}
	
	public void setDate(String date) {
		this.date = date;
	}
	public String getMode() {
		return mode;
	}
	public void setMode(String mode) {
		this.mode = mode;
	}
	public String getUnit() {
		return unit;
	}
	public void setUnit(String unit) {
		this.unit = unit;
	}
	public String getCurrent() {
		return current;
	}
	public void setCurrent(String current) {
		this.current = current;
	}
	public String getInteractive() {
		return interactive;
	}
	public void setInteractive(String interactive) {
		this.interactive = interactive;
	}

	@Override
	public String toString() {
		return "Item [current=" + current + ", date=" + date + ", interactive="
				+ interactive + ", mode=" + mode + ", unit=" + unit + "]";
	}
}

			

The following reads the XML file and creates a List of object Items from the entries in the XML file.

				
package de.vogella.xml.stax.read;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Attribute;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;

import de.vogella.xml.stax.model.Item;

public class StaXParser {
	static final String DATE = "date";
	static final String ITEM = "item";
	static final String MODE = "mode";
	static final String UNIT = "unit";
	static final String CURRENT = "current";
	static final String INTERACTIVE = "interactive";

	@SuppressWarnings({ "unchecked", "null" })
	public List<Item> readConfig(String configFile) {
		List<Item> items = new ArrayList<Item>();
		try {
			// First create a new XMLInputFactory
			XMLInputFactory inputFactory = XMLInputFactory.newInstance();
			// Setup a new eventReader
			InputStream in = new FileInputStream(configFile);
			XMLEventReader eventReader = inputFactory.createXMLEventReader(in);
			// Read the XML document
			Item item = null;

			while (eventReader.hasNext()) {
				XMLEvent event = eventReader.nextEvent();

				if (event.isStartElement()) {
					StartElement startElement = event.asStartElement();
					// If we have a item element we create a new item
					if (startElement.getName().getLocalPart() == (ITEM)) {
						item = new Item();
						// We read the attributes from this tag and add the date
						// attribute to our object
						Iterator<Attribute> attributes = startElement
								.getAttributes();
						while (attributes.hasNext()) {
							Attribute attribute = attributes.next();
							if (attribute.getName().toString().equals(DATE)) {
								item.setDate(attribute.getValue());
							}

						}
					}

					if (event.isStartElement()) {
						if (event.asStartElement().getName().getLocalPart()
								.equals(MODE)) {
							event = eventReader.nextEvent();
							item.setMode(event.asCharacters().getData());
							continue;
						}
					}
					if (event.asStartElement().getName().getLocalPart()
							.equals(UNIT)) {
						event = eventReader.nextEvent();
						item.setUnit(event.asCharacters().getData());
						continue;
					}

					if (event.asStartElement().getName().getLocalPart()
							.equals(CURRENT)) {
						event = eventReader.nextEvent();
						item.setCurrent(event.asCharacters().getData());
						continue;
					}

					if (event.asStartElement().getName().getLocalPart()
							.equals(INTERACTIVE)) {
						event = eventReader.nextEvent();
						item.setInteractive(event.asCharacters().getData());
						continue;
					}
				}
				// If we reach the end of an item element we add it to the list
				if (event.isEndElement()) {
					EndElement endElement = event.asEndElement();
					if (endElement.getName().getLocalPart() == (ITEM)) {
						items.add(item);
					}
				}

			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (XMLStreamException e) {
			e.printStackTrace();
		}
		return items;
	}

}

			

You can test the parser via the following test program. Please note that the file config.xml must exist in the Java project folder.

				
package de.vogella.xml.stax.read;

import java.util.List;

import de.vogella.xml.stax.model.Item;

public class TestRead {
	public static void main(String args[]) {
		StaXParser read = new StaXParser();
		List<Item> readConfig = read.readConfig("config.xml");
		for (Item item : readConfig) {
			System.out.println(item);
		}
	}
}

			

This example is stored in project "de.vogella.xml.stax.writer".

Lets assume you would like to write the following simple XML file.

				
<?xml version="1.0" encoding="UTF-8"?>
<config>
	<mode>1</mode>
	<unit>900</unit>
	<current>1</current>
	<interactive>1</interactive>
</config>

			

StaX does not provide functionality to format the XML file automatically. So you have to add end-of-lines and tab information to your XML file.

				
package de.vogella.xml.stax.writer;

import java.io.FileOutputStream;

import javax.xml.stream.XMLEventFactory;
import javax.xml.stream.XMLEventWriter;
import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Characters;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartDocument;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;

public class StaxWriter {
	private String configFile;

	public void setFile(String configFile) {
		this.configFile = configFile;
	}

	public void saveConfig() throws Exception {
		// Create a XMLOutputFactory
		XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
		// Create XMLEventWriter
		XMLEventWriter eventWriter = outputFactory
				.createXMLEventWriter(new FileOutputStream(configFile));
		// Create a EventFactory
		XMLEventFactory eventFactory = XMLEventFactory.newInstance();
		XMLEvent end = eventFactory.createDTD("\n");
		// Create and write Start Tag
		StartDocument startDocument = eventFactory.createStartDocument();
		eventWriter.add(startDocument);

		// Create config open tag
		StartElement configStartElement = eventFactory.createStartElement("",
				"", "config");
		eventWriter.add(configStartElement);
		eventWriter.add(end);
		// Write the different nodes
		createNode(eventWriter, "mode", "1");
		createNode(eventWriter, "unit", "901");
		createNode(eventWriter, "current", "0");
		createNode(eventWriter, "interactive", "0");

		eventWriter.add(eventFactory.createEndElement("", "", "config"));
		eventWriter.add(end);
		eventWriter.add(eventFactory.createEndDocument());
		eventWriter.close();
	}

	private void createNode(XMLEventWriter eventWriter, String name,
			String value) throws XMLStreamException {

		XMLEventFactory eventFactory = XMLEventFactory.newInstance();
		XMLEvent end = eventFactory.createDTD("\n");
		XMLEvent tab = eventFactory.createDTD("\t");
		// Create Start node
		StartElement sElement = eventFactory.createStartElement("", "", name);
		eventWriter.add(tab);
		eventWriter.add(sElement);
		// Create Content
		Characters characters = eventFactory.createCharacters(value);
		eventWriter.add(characters);
		// Create End node
		EndElement eElement = eventFactory.createEndElement("", "", name);
		eventWriter.add(eElement);
		eventWriter.add(end);

	}

}

			

And a little test.

				
package de.vogella.xml.stax.writer;

public class TestWrite {

	public static void main(String[] args) {
		StaxWriter configFile = new StaxWriter();
		configFile.setFile("config2.xml");
		try {
			configFile.saveConfig();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

			

For another (more complex example of using Stax please see Reading and creating RSS feeds via Java (with Stax)