A minor version difference between the number 1012 and 1013, however the underlying mechanisms and libraries have huge changes.
|Corresponding JDeveloper Version||JDeveloper 1012||JDeveloper 1013|
|Clustering||Manual joining server farm via EM||Dynamic Discovery with broadcasting address in opmn.xml|
|JSF Support||Need extra tweaking||Supported|
|WEB-INF/web.xml||(plain)||Define namespace such as xmlns:xsi, xsi:schemaLocation, etc, which is not compatible with AS1012|
|Misc Java libraries||Working with JDK1.4.2||Working with JDK1.5. Not completely compatible with AS1012.|
|Startup||opmnctl and emctl||opmnctl|
The above are the list of difference I have encountered.
What it means is that, at this point of time when you develop web application, you need to explicitly synchronize Oracle AS version and environment.
For example, you use JDeveloper 1013 to develop web application and deploy it into OracleAS1013 only. If you try to deploy it into AS1012, it is very problematic. You need to manually edit web.xml and bundle older underlying libraries (such as classes12.jar) into your EAR file.