JAXb, Hibernate and beans

Question

Currently I am working on a project with Spring web-service, hibernate and JAXb.

1) I have generated hibernate beans using IDE 'hibernate code generation,

2) also, I have generated the jaxb beans using maven compiler.

..

Now, my question is,

1) Is this the right approach? (to have so many beans).

2) Shall I use JAXb beans for processing into the service layer? How can I keep layers decoupled?

3) Or, do I need to create another set of beans ie. map (JAXb beans) to (new beans) to (hibernate beans)?

.

Please tell your views?

Thanks, adi

Answer 1

You know, you cannot have everything fully decoupled. There will be always a layer that will know the other two layers.

Usually when I design 3 layers architecture, like:

1. Service Layer - the one that probably uses JAXB, exposes web services or other APIs
2. Business Layer - any real logic
3. Persistence Layer - hibernate

I allow the Business layer to know about the Service Layer (JAXB) and about the Persistence Layer (hibernate beans). But I don't allow the Service Layer and the Persistence Layer to know about each other.

Answer 2

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group. EclipseLink also provides an excellent JPA implementation (open sourced from TopLink).

There are costs to maintaining multiple models. Each model you add introduces a bean-to-bean conversion that must be written, tested, and maintained.

Another approach is to use the same beans for both the JPA and JAXB bindings. For this use case it will be easier to start with domain model and add JAXB & JPA metadata to apply mappings to XML and the database. Below is example of where a single model is leveraged to create a RESTful web service:

• http://blog.bdoughan.com/2010/08/creating-restful-web-service-part-35.html

Since EclipseLink provides both JAXB and JPA implementations we provide a number of extensions to make this easier:

• http://wiki.eclipse.org/EclipseLink/Examples/MOXy/JPA
• http://blog.bdoughan.com/2010/07/jpa-entities-to-xml-bidirectional.html

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UPDATE

In response to:

Agree to what you are saying. However, using same beans will couple the code very tightly and will be highly dependent. Change in one layer will need changes elsewhere as well. What you say?

It all depends how you look at things. My preference for building data access services is to design and build a solid domain model. Then use JPA and JAXB to solve the impedance mismatches between object-relational and object-XML.

One Model Approach

Using one model for both JPA and JAXB means that when you make a change to the model you need to decide at that time how it will be handled for both JPA and JAXB (this can be good or bad). If you don't want every new addition to the model to affect the JAXB mapping you can leverage JAXB concepts like @XmlAccessorType(XmlAccessType.NONE).

• http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html

Two (or More) Models Approach

When you want to add a field that is mapped to both relational and XML you need to add it to two models and add the necessary conversion logic. In this case there is a cost to keeping the models de-coupled.