JiBX - Part 1

When we consider XML as a data model while programming, focus is mostly given on strings/tags/elements in parsing data.The ETL operations are done on this ubiquitous document interchange model when communication is made between applications.To make things simple in the internet; which is fond of documents ; XML became the foundation of services through web.The object, which is accessed from object graphs in the memory have features such as inheritance / polymorphism and attributes / object-based relationships while XML does not have any of these features as objects have.It is merely a grammatical (hierarchical) representation of data with all its branches mangled to itself .But they have similarity in the sense of representation of real world data.Therefore they can exists as the representation of each other which eases in programming.They are effective in defining business uses cases.But there is an impedance mismatch between objects and xmls.An application written in Java, will have it data types defined within the scope while XML Schema which defines the data is richer than Java.Complex objects find difficulty in serializing.Have a look on this paper which explains the X/O impedance mismatch.

We can generate Java classes from XML or vice versa.In this case, it is a "Schema-Centric" approach.We define an XML schema.Then one or more XML documents.Then generate java classes based on them.In this case you need a stable schema which can be used to validate data.Essential for a "reliable" web service.But application code is forced to use an interface that reflects the XML structure which makes them tightly coupled to contracts defined.Any change in schema make a need to regenerate the object model and change application code to match.

If we map the classes using bindings, then its "Java technology-centric " approach.This can be adopted when you don't want object model tied to schema.When there is a need to support different versions of the schema with the same object model or a common data exchange format for existing objects is needed.Binding definitions are themselves XML documents, with a schema defined for it.

JiBX is fundamentally a Java technology-centric (mapped binding) approach uses binding definitions.You define how XML relates to Java objects.Start from schema, code, or both.Binding code is compiled (or wired ?) into files (which uses BCEL byte code enhancements ). It can be done at build time, or on-the-fly at runtime.This makes JiBX compact and fast.JiBX achieves its performance by using post-compilation bytecode manipulation rather than the reflection.The advantage is that there is no need for getters, setters and no-arg constructors.One can write the class without considering mapping issues and then map it without modifications. XML schema describe domain objects.JiBX really maps well to XSD. JiBX is based on a XML pull parser architecture (XPP3) . Rather than generating code from a DTD or Schema, JiBX works with a binding definition that associates user-supplied classes with XML structure. The binding compiler is executed after code is compiled and the marshalling/unmarshalling code is added on to the class files.There are tools along with it, like Bindgen that can generate schema from existing classes.


Pdfs - JiBX -Part1 JiBX-Part2 Intro

Previous articles
Creating a Java WebService using Axis 2 (a lazy approach)
A simple RSS parser

No comments:

Post a Comment