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Session EJB
Entity EJB
Ask for data bean
Get information from EJB
Set copy of
Obtain data
for display
Figure 8.6 This sequence diagram is characteristic of the facade design pattern. The distributed
interface appears just before the session EJB. Note that the communication is reduced to a single
call. (Actually, one additional call at lower levels is required to initialize the communication with
the stateless session bean.)
mechanisms with our command architecture, or we can use session EJB s. The
key is to reduce chatty interfaces by collecting multiple communications
around a single point.
Roots of round-tripping
As all beginners on the riverbanks watch, the pour-over cartwheels Eric's kayak
several terrifying times before finally releasing him. Frantically, we fumble for
ropes and throw one end uselessly behind him. Suddenly Eric rolls up, effortlessly,
without his paddle. The beginners now see Eric's mishap in a different light: he
didn't blunder over the pour-over--he aggressively fought the current to get his
boat right in that monstrous maw in the river. He then bravely disdained his sole
means of control and propulsion, as if to say, “I don't need a stinking paddle.” He
executed some carefully planned linked moves in the hydraulic, disengaged, and
did an Eskimo roll, sans paddle. On this day, Eric is everyone's paddling idol.
When Eric went into his first rapid, he was equipped with a new tool: a hands
Eskimo roll. It was an advanced technique that few had mastered, and one that
gave him a false sense of security. He went into the rapid underequipped and
overconfident. Though his roll worked in this instance, he knew it wouldn't be
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