How to deserialize Java objects from XML?

Question

I\'m sure this might have been discussed at length or answered before, however I need a bit more information on the best approach for my situation...

Problem

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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;

}

Answer 5

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