How to deserialize Java objects from XML?

Use XSLT to transform the large XML files into a local domain model that is mapped to java objets with JAXB.

Start with the JDK 5+ built in XML libraries (unless you absolutely need XSLT 2.0, in which case use Saxon)

Don't focus on relative performance of SAX/DOM, focus on learning how to write XPath expressions and use XSLT, and then worry about performance later if and only if you find it to be a problem.

The Eclipse XML editors are decent, but if you can afford it, spring for Oxygen XML, which will let you do XPath evaluation in realtime.

We had a similar situation and I just threw together some XPath code that parsed the stuff I needed.

It was amazingly quick even on 100k+ XML files. We went as low tech as possible. We handle around 1000 files a day of that size and parsing time is very low. We have no memory issues, leaks etc.

We wrote a quick prototype in Groovy (if my memory is accurate) - proof of concept took me about 10 minutes

JAXB, the Java API for XML Binding might be what you want. You use it to inflate an XML document into a Java object graph made up of "Java content objects". These content objects are instances of classes generated by JAXB to match the XML document's schema

But if you already have a set of Java classes, or don't yet have a schema for the document, JAXB probably isn't the best way to go. I'd suggest doing a SAX parse and then building up your Java objects during the parse. Alternatively you could try a DOM parse and then walk the resulting Document tree to pull out the parts of interest (maybe with XPath) -- but 5MB of XML might turn into 50MB of DOM tree objects in Java.

DOM, SAX and XSLT are different animals.

DOM parsing loads the entire document into memory, which for 100K to 5MB (very small by today's standards) would work.

SAX is a stream parser which reads the XML and delivers events to your code for each tag.

XSLT is a system for transforming one XML tree into another. Even if you wrote a transform that converts the input to a more suitable format, you'd still have to write something using DOM or SAX to convert it into Java objects.

You can use the @XmlPath extension in EclipseLink JAXB (MOXy) to easily handle this use case. For a detailed example see:

• http://bdoughan.blogspot.com/2010/09/xpath-based-mapping-geocode-example.html

Sample Code:

package blog.geocode;

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement(name="kml")
@XmlType(propOrder={"country", "state", "city", "street", "postalCode"})
public class Address {

    @XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:Thoroughfare/ns:ThoroughfareName/text()")
    private String street;

    @XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:LocalityName/text()")
    private String city;

    @XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:AdministrativeAreaName/text()")
    private String state;

    @XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:CountryNameCode/text()")
    private String country;

    @XmlPath("Response/Placemark/ns:AddressDetails/ns:Country/ns:AdministrativeArea/ns:SubAdministrativeArea/ns:Locality/ns:PostalCode/ns:PostalCodeNumber/text()")
    private String postalCode;

}