Annotation processing tool generates source code for a metamodel class given 
the annotated source code of persistent entity. 
This tool is invoked during compilation for JDK6 compiler if OpenJPA and JPA 
libraries are specified in the compiler -classpath option and
Annotation processor option -Aopenjpa.metamodel=true is specified.
    
 $ javac -classpath path/to/openjpa-all.jar -Aopenjpa.metamodel=true mypackage/MyEntity.java
    
will generate source code for canonical meta-model class mypackage.MyEntity_.
The source code is generated relative to the directory specified in -s option
of javac compiler and defaulted to the current directory.
      
The Annotation Processor recognizes the following options specified in the command-line with -A 
(none of them are mandatory).
    
              -Aopenjpa.log=TRACE|INFO|WARN|ERROR : The logging level. Default is WARN.
            
             -Aopenjpa.source=<n> : where <n> denotes the integral number for Java source 
             version of the generated code. Default is 6.
             
               -Aopenjpa.naming=class name : fully-qualified name of a class implementing 
               org.apache.openjpa.meta.MetaDataFactory that determines
the name of a meta-class given the name of the original persistent Java entity class. Defaults to
org.apache.openjpa.persistence.PersistenceMetaDataFactory which appends a underscore character
(_) to the original Java class name. 
             
               -Aopenjpa.header=<url> : A url whose content will appear as comment header to the generated file(s). 
               Recognizes special value ASL for Apache Source License header as comment. 
               By default, adds a OpenJPA proprietary text as comment block.