Java Architecture for XML Binding (JAXB)

Java Architecture for XML Binding (JAXB)

Q. What is Java Architecture for XML Binding (JAXB)?

A. The Java Architecture for XML Binding (JAXB) simplifies the creation and maintenance of XML-enabled Java applications. JAXB provides a binding compiler and a runtime framework to support a two-way mapping between XML documents and Java objects. The binding compiler translates W3C XML Schema into one or more Java classes without requiring the developer to write complex parsing code. The schema-derived classes and binding framework enable error and validity checking of incoming and outgoing XML documents, thereby making it possible to ensure that only valid, error-free messages are accepted, processed, and generated by a system. For more information, see the Reference Implementation and the Public Draft Specification, both available for download from the JAXB homepage.

Q. What is the difference between JAXB, SAX, and DOM? Which one should I use?

A. SAX is an event-driven XML parser that is appropriate for high-speed processing of XML because it does not produce a representation of the data in memory. DOM, on the other hand, produces an in-memory data representation, which allows an application to manipulate the contents in memory. Both SAX and DOM automatically perform structure validation. An application could perform content validation with SAX and DOM, but such an application must provide the necessary extra code, which might be complicated, error-prone, and difficult to maintain.

A JAXB application can perform structure and content validation with Java classes that it generates from a schema. A JAXB application builds an in-memory data structure, like a DOM, by marshalling an XML document to build a content tree, which contains objects that are instances of the derived classes. However, unlike a DOM tree, a content tree is specific to one source schema, does not contain extra tree-manipulation functionality, allows access to its data with the derived classes' accessor methods, and is not built dynamically. For these reasons, a JAXB application uses memory more efficiently than a DOM application does. If the content of a document is more dynamic and not well-constrained, DOM and SAX are more appropriate than JAXB for processing XML content that does not have a well-known schema prior to processing the content.

Q. How does JAXB work?

A. To build a JAXB application, start with an XML schema. The beta release requires that the schema language be W3C 2001 Recommendation for XML Schema.


After obtaining an XML Schema, you build and use a JAXB application by performing these steps:

Generate the Java source files by submitting the XML Schema to the binding compiler.

You can use custom binding declarations to override the default binding of XML Schema components to Java representations

Compile the Java source code.

With the classes and the binding framework, write Java applications that:

Build object trees representing XML data that is valid against the XML Schema by either unmarshalling the data from a document or instantiating the classes you created.

Access and modify the data.

Optionally validate the modifications to the data relative to the constraints expressed in the XML Schema

Marshal the data to new XML documents.

Q. Who is involved in developing JAXB?

A. JAXB is being developed through the Java Community Process (JCP) with an expert group consisting of IBM, Software AG, BEA Systems, Hewlett-Packard, TIBCO Software Inc., Oracle, Fujitsu Limited, Breeze Factor LLC, Macromedia, Inc. and Intalio, Inc. Sun is an active member of the W3C XML Schema Working Group and is also working with other industry consortia such as OASIS and xml.org.

Q. Where can I read more about JAXB?

A. For a higher-level explanation of JAXB, refer to the JAXB chapters in the Java Web Services Tutorial. Also note that a detailed user's guide is included as part of the JAXB distribution. For a more technical and detailed description of JAXB, see the the latest version of the Specification, which you can download from the JAXB homepage. Please note that the Specification is in Adobe Acrobat PDF format. Download Adobe Acrobat for free.