Java2WSDL vs WSDL2Java its a long debate.
Theory: People say, it is better to have contract first and develop XSD. later generate code.
1. Working on XML tools and generating XSD is painful process.
2. We never use simple data types in real projects
3. Dont have much time to do small POCs, when depending on WSDL2Java (Proof of Concepts)
4. Difficult to handle frequent changes
Reality: Do your work using Java coding. Develop all business objects, ..etc.
Once you are confident and ready to interface with other applications go with Java2WSDL.
Java2WSDL wins and saves time for developers.
Here is the Maven Java2WSDL plugin (cxf-java2ws-plugin) for your reference.
cxf-java2ws-plugin : http://cwiki.apache.org/CXF20DOC/maven-java2ws-plugin.html
WSDL Document Structure: http://www.w3schools.com/WSDL/wsdl_documents.asp