Chapter 13. The Seam Application Framework

Seam makes it easy to create applications with annotated plain Java classes. We can make common programming tasks even easier by providing a set of pre-built components that are reusable with configuration or extension.
The Seam Application Framework can reduce the amount of code you need to write in a web application for basic database access with either Hibernate or JPA. The framework contains a handful of simple classes that are easy to understand and to extend where required.

13.1. Introduction

The components provided by the Seam Application Framework can be used in two separate approaches. The first approach is to install and configure an instance of the component in components.xml, as with other built-in Seam components. For example, the following fragment (from components.xml) installs a component that performs basic CRUD operations for a Person entity: 
<framework:entity-home name="personHome" entity-class="eg.Person" 
           entity-manager="#{personDatabase}"> 
<framework:id>#{param.personId}</framework:id> 
</framework:entity-home>
If this approach seems too XML-heavy, you can approach this through extension: 
@Name("personHome") 
public class PersonHome extends EntityHome<Person> { 
@In EntityManager personDatabase; 
  public EntityManager getEntityManager() { 
    return personDatabase; 
  } 
}
The major advantage to the second approach is that the framework classes were designed for extension and customization, so it is easy to add extra functionality or override the built-in functionality.
Another advantage is that you have the option of using EJB stateful session beans (or plain JavaBean components) as your classes: 
@Stateful 
@Name("personHome") 
public class PersonHome extends EntityHome<Person> 
                        implements LocalPersonHome { }
You can also make your classes stateless session beans. In this case you must use injection to provide the persistence context, even if it is called entityManager: 
@Stateless 
@Name("personHome") 
public class PersonHome extends EntityHome<Person> 
                        implements LocalPersonHome { 
  @In EntityManager entityManager; 
  public EntityManager getPersistenceContext() { 
    entityManager; 
  } 
}
At present, the Seam Application Framework provides four main built-in components: EntityHome and HibernateEntityHome for CRUD, and EntityQuery and HibernateEntityQuery for queries.
The Home and Query components are written so that they can be session-, event- or conversation-scoped. The scope depends upon the state model you wish to use in your application.
The Seam Application Framework works only with Seam-managed persistence contexts. By default, components will expect a persistence context named entityManager.