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RE: [wtp-dev] Java EE 5 models design overview

Title: Java EE 5 models design overview
Hi Shaun,
 
The Dali project was the place where I looked how annotation processing is done. After reviewing the tools in the org.eclipse.dali.core.util.jdt package I came to the idea to use the AST API.
 
May be a common package for annotation processing that is placed down in org.eclipse.jst will be of great benefit for many WTP components.
 
Can you provide some overview what is covered by the Dali tools for annotations and xml descriptors processing?
 
Thanks and greetings
Kaloyan


From: wtp-dev-bounces@xxxxxxxxxxx [mailto:wtp-dev-bounces@xxxxxxxxxxx] On Behalf Of Shaun Smith
Sent: Tuesday, November 14, 2006 9:16 PM
To: General discussion of project-wide or architectural issues.
Cc: General Dali EJB ORM developer discussion.
Subject: Re: [wtp-dev] Java EE 5 models design overview

I just want to point out that the Dali team has been dealing with the Java Annotation/XML Descriptor combination issue for some time, as this is how object-relational mappings are defined in JPA, and has a fair amount of expertize in this area.  Dali 0.5 has annotation support with XML support under development for 1.0.  Neil Hauge has previously solicited feedback on dealing with this issue.  Nothing much came of that effort so we've been patiently waiting for other teams to "hit the wall" on this so that we could start building the community of projects requiring Java 5 annotations that would be large enough to push for better annotation support from the platform projects we all rely on.

    Shaun
 
Raev, Kaloyan wrote:

Hello,

This is a follow up of the WTP 2.0 Requirements meeting held on 26 Oct:
http://wiki.eclipse.org/index.php/2006-10-26_wtp-requiremements-minutes

I want to present an overview of my vision how Java EE 5 models should be implemented in WTP.

Currently, there are J2EE 1.4 models implemented in WTP. These are EMF models generated from the deployment descriptors' XML Schemas of the J2EE 1.4 specification. Overview of the J2EE 1.4 models is presented in the following page:

http://www.eclipse.org/webtools/jst/components/j2ee/api/j2ee_models_overview.html

Java EE 5 models should be implemented in a similar way. The EMF models should utilize the new deployment descriptors' XML Schemas from the Java EE 5 specification. Additional complexity to the models is added by the fact that the Java EE 5 specification uses Java Annotations in addition to the deployment descriptors. Therefore, the problematic shifts on how to integrate these annotations to the EMF model.

It was a natural approach that I had a look to the JEM (Java EMF Model) project. JEM contains functions for modeling Java classes in EMF. Unfortunately, JEM does not cover Java Annotations at the moment and there is no plan for the future yet:

http://dev.eclipse.org/newslists/news.eclipse.tools.ve/msg05989.html

There are to approaches to model Java Annotations:
1. Extend JEM with new features to cover Java Annotations and integrate both EMF models (the other one is the one generated from the XML Schemas).

2. Implement custom utility to parse and index Java Annotation from the source files and make the EMF model (made from XML Schemas) to use it.

Due to the lack of any documentation in the JEM project, approach 1. is feasible only long-term. This is why I want to concentrate on approach 2.

Now, the Java EE 5 models problem can be split in the following tasks:
1. Build an EMF model based on the deployment descriptors' XML Schemas.
2. Parse Java Annotations from the Java files.
3. Index the parsed annotations in a way they can be easily retrieved.
4. Make the EMF model to be influenced by the available annotations.
5. Update Java Annotation with changes on the EMF model.

Task 1. Build an EMF model based on the deployment descriptors'' XML Schemas.
This can be done easily with the available toolset provided by the EMF project. The EMF model is generated by the XML Schemas for the Java EE 5 deployment descriptors. A problem appears if we want to split the generated classes in separate packages for better structure:

http://www.eclipse.org/newsportal/article.php?id=20770&group=eclipse.tools.emf#20770

However, this problem is solvable at least with manual refactoring of the generated classes.

Task 2. Parse Java Annotations from the Java files.
Here Java files can be:
  - Java Class files in JAR library in the classpath;
  - Java source files in the Eclipse project.

Java Annotations from the Java Class files can be easily parsed using the Sun's Java Reflect API.
Java Annotations from the Java source files can be parsed using the Java DOM/AST API provided by the Eclipse JDT Core project. The latter API models the Java source code as a structured document. There, annotations are treated as member modifiers (like public, private, static, final, etc.). There is a function that checks if a modifier is an annotation.

The parser utility will listen to events to trigger the parsing process:
  - ResourceChangeListener/Event - notifies for resource changes in the workspace: project open/close, files added/deleted, etc;

  - ElementChangedListener/Event - notifies for changes in the Java Editor. The parser will be notified that the user has changed a java file in the editor and it has to be reparsed for changes in the annotations.

Task 3. Index the parsed annotations in a way they can be easily retrieved.
The parser will update an appropriate structure with the added or removed annotations. The structure should allow quick and flexible way to retrieve the indexed annotation. For beginning even an ArrayList that holds references to the org.eclipse.jdt.core.dom.Annotation objects is enough. Annotation objects hold references to the parent Java members and parent workspace resources and that should be all the information we need. Of course, the ArrayList is far away from the optimal solution and it should be optimized later with a better structure.

Task 4. Make the EMF model to be influenced by the available annotations.
The generated EMF model from the deployment descriptors' XML Schemas will be modified in a way that it not only looks into the XML data, but also looks up the Annotation Model utility for the corresponding annotation. If there are such annotations indexed, the EMF model will update it state appropriately. The Annotation Model utility also has to provide notification framework, so the EMF model to register a listener and be notified with events on changes in the annotation model.

5. Update Java Annotation with changes on the EMF model.
Properties in the EMF model now declared in two sources: XML files and Java Annotations. When this property is changes it has to be updated in the same source. If the property is declared in XML then its new value has to be updated again in the XML file. If the property is declared as a Java Annotation it has to be updated again in the same Java Annotation.

To achieve the above, the EMF model has to be changed in a way that it remembers the source type of each property.
Updating Java Annotation will be done again using the Java DOM/AST API.


This is the overview for the moment. I want to here your comments. Especially, I want to hear your opinion about the "Extending JEM" <--> "Custom Annotation Model utility" dilemma. Due to the lack of documentation, my knowledge to JEM is not enough and I cannot estimate the effort to extend it with Java Annotation support. This is why I prefer the latter approach that I have described in more details.

There are no comments about the UI from my side for the moment. Here your comments would be also interesting. Do we stick to the Deployment Descriptor node in the Project Navigator? What features would be needed there for future enhancements?

Greetings,
Kaloyan Raev
Senior Developer
NW AS JS TOOLS JEE (BG)
SAP Labs Bulgaria
T +359/2/9157-416
mailto:kaloyan.raev@xxxxxxx
www.sap.com


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