In this chapter we covered the basic usage of the validation framework, its built-in validations, and how to expand it by creating custom constraints. We also covered how to insert records to a database using JPA and JTA along with considerations about transaction isolation and the different ways of dealing with a transaction. Furthermore, we looked at how to expose web services using SOAP; how to generate a web service client with WebLogic's utility, adding it to our business scenario; and how to implement and configure singleton session beans to control concurrency.
In the next chapter, we will take a tour of the event system available to Java EE applications, understanding and using events and interceptors, among other features.