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I'm new to using JAXB, and I used JAXB 2.1.3's xjc to generate a set of classes from my XML Schema. In addition to generating a class for each element in my schema, it created an ObjectFactory class.
There doesn't seem to be anything stopping me from instantiating the elements directly, e.g.
MyElement element = new MyElement(); whereas tutorials seem to prefer
MyElement element = new ObjectFactory().createMyElement(); If I look into ObjectFactory.java, I see:
public MyElement createMyElement() { return new MyElement(); } so what's the deal? Why should I even bother keeping the ObjectFactory class around? I assume it will also be overwritten if I were to re-compile from an altered schema.
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jaxb package. An ObjectFactory allows you to programatically construct new instances of the Java representation for XML content. The Java representation of XML content can consist of schema derived interfaces and classes representing the binding of schema type definitions, element declarations and model groups.
The ObjectFactory class is part of the primer. po package. ObjectFactory provides factory methods for instantiating Java interfaces representing XML content in the Java content tree. Method names are generated by concatenating: The string constant create.
The content tree of data objects represents the structure and content of the source XML documents. You can use the set methods defined for a class to modify the content of elements and attributes. Marshal Java content objects back to XML.
JAXB stands for Java Architecture for XML Binding. It provides mechanism to marshal (write) java objects into XML and unmarshal (read) XML into object. Simply, you can say it is used to convert java object into xml and vice-versa.
Backward compatibility isn't the only reason. :-P
With more complicated schemas, such as ones that have complicated constraints on the values that an element's contents can take on, sometimes you need to create actual JAXBElement objects. They are not usually trivial to create by hand, so the create* methods do the hard work for you. Example (from the XHTML 1.1 schema):
@XmlElementDecl(namespace = "http://www.w3.org/1999/xhtml", name = "style", scope = XhtmlHeadType.class) public JAXBElement<XhtmlStyleType> createXhtmlHeadTypeStyle(XhtmlStyleType value) { return new JAXBElement<XhtmlStyleType>(_XhtmlHeadTypeStyle_QNAME, XhtmlStyleType.class, XhtmlHeadType.class, value); } This is how you get a <style> tag into a <head> tag:
ObjectFactory factory = new ObjectFactory(); XhtmlHtmlType html = factory.createXhtmlHtmlType(); XhtmlHeadType head = factory.createXhtmlHeadType(); html.setHead(head); XhtmlStyleType style = factory.createXhtmlStyleType(); head.getContent().add(factory.createXhtmlHeadTypeStyle(style)); The first three uses of the ObjectFactory could be considered superfluous (though useful for consistency), but the fourth one makes JAXB much, much easier to use. Imaging having to write a new JAXBElement out by hand each time!
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