8. As noted earlier, stateless session beans model tasks don’t maintain conversational state . This means that session beans model tasks can be completed in a single method call, such as placing a bid. However, this does not mean that all stateless session beans contain a single method.<o:p></o:p>
9. Three types of business interfaces correspond to the different access types:<o:p></o:p>
Local interface<o:p></o:p>
A local interface is designed for clients of stateless session beans collocated in the same container (JVM) instance.<o:p></o:p>
Remote interface<o:p></o:p>
Clients residing outside the EJB container’s JVM instance must use some kind of remote interface. Remote business interfaces do have one special requirement: all parameters and return types of interface methods must be Serializable. This is because only Serializable objects can be sent across the network using RMI.<o:p></o:p>
<o:p>?</o:p>
Web service endpoint interface<o:p></o:p>
The third type of interface is specific to stateless session beans that you haven’t seen yet: the web service endpoint interface (also known as SEI). The ability to expose a stateless session bean as a SOAP-based web service is one of the most powerful features of EJB 3.<o:p></o:p>
10. Stateful session beans are guaranteed to maintain conversational state.<o:p></o:p>
11. Since stateful session beans cannot be pooled and reused like stateless<o:p></o:p>
beans, there is a real danger of accumulating too many of them if we don’t have a way to destroy them. Therefore, we have to define a business method for removing the bean instance by the client using the @Remove annotation.<o:p></o:p>
( 由于有狀態 session bean 不能像無狀態 session bean 放入對象池而重復使用 , 所以如果我們不能及時銷毀，就會累積許多的風險。我們必須使用 @Remove 標注來定義一個業務方法去移去 bean 實例。 )<o:p></o:p>
12.A stateful session bean cannot have a web service endpoint interface.<o:p></o:p>
This is because SOAP-based web services are inherently stateless in nature.( 有狀態 session bean 不能實現 web 服務 endpoint 接口，這是由于基于 SOAP 的 web 服務本質上是無狀態的。 )<o:p></o:p>
13<o:p></o:p>
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<o:p>?
</o:p>
14. To outline some of the best practices for session beans: ??? <o:p></o:p>
n ?????? Choose your bean type carefully. Stateless session beans will be suitable most of the time.( 認真選擇 session 的類型，在大多時候無狀態 session bean 是最適合的。 )<o:p></o:p>
n ?????? Carefully examine interface types for session beans. Remote interfaces involve network access and may slow down your applications.( 仔細檢查 session bean 的接口類型。如果是遠程接口必須訪問網絡，這樣會減慢系統的訪問速度。 )<o:p></o:p>
n ?????? If you are using DI, make sure you don’t inject a stateful session bean into a stateless session bean or servlet.( 如果你使用依賴注入，確保不要將有狀態 session bean 注入到無狀態 session bean 或 servlet 中。 )<o:p></o:p>
n ?????? Separate crosscutting concerns such as logging and auditing using business interceptors (which we discuss in chapter 5) instead of spreading them all over the business logic.( 使用攔截器代替在整個業務邏輯中傳遞，來分離像日志和審核等之類的橫關切點 )<o:p></o:p>
n ?????? Closely examine what kind of data you are storing in the conversation state. Try to use small, primitive instance variables in a stateful bean whenever possible as opposed to large nested composite objects.<o:p></o:p>
n ?????? Don’t forget to define remove methods in a stateful session bean.<o:p></o:p>
n ?????? Tune passivation and timeout configurations to find the optimal values for your application.( 調整純化和超時配置，以錄求系統最佳性能。 ) <o:p></o:p>
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