Using an exposed domain model - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 295

8.2 Managing connections using a Spring filter

Lazy loading requires the persistence framework connection— JDO Persistence-
Manager or Hibernate Session —used to load the root object to remain open. When
the application traverses a relationship to an unloaded object, the persistence
framework uses that connection to load it. Consequently, when using the Exposed
Domain Model pattern the application must keep the persistence framework con-
nection open while handling a request in order to allow the view components to
load objects lazily. We have seen that a good way to accomplish this is to use a serv-
let filter, which intercepts requests and opens the connection, executes the servlet
and the JSP page, and closes the connection. Figure 8.4 shows how a request is han-
dled in an application that uses a servlet filter to manage connections.

:Web
Container

:Persistence
Framework

:Domain
Object

:Filter :Servlet :JSP

doFilter()

getConnection()

service()

<<forward>>

closeConnection()

Figure 8.4 Using a servlet filter to handle connections