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Performance considerations for stateful beans
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instance to 100 and we usually have 150 active clients, the container will continue to passivate and activate bean instances, thus causing performance problems. You can go a long way toward solving potential memory problems by explicitly removing the no longer required bean instances rather than depending on the container to time them out. As discussed earlier, you can annotate a method with the @Remove annotation that signals the container to remove the bean instance. Given the fact that stateful session beans can become performance bottlenecks whether through improper usage or under certain circumstances, it is worth inspecting the alternatives to using them.
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3.5.2 Stateful session bean alternatives
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This section examines a few alternative strategies to implementing stateful business processing, as well as some issues you may need to consider when using them. The first alternative to stateful beans is replacing them with a combination of persistence and stateless processing. In this scheme, we essentially move state information from memory to the database on every request. You should carefully examine whether you want to maintain state between conversations in memory. Base your decision completely based on your application requirements and how much tolerance of failure you have. For example, in the BidderAccountCreator EJB you can probably avoid the use of conversational state by not maintaining instance variables to store the user information in memory and save data in the database on each method call. Second, you may choose to build some mechanism at the client side to maintain state. This requires additional coding, such as storing the state as an object in client memory or in a file. The downside of these two approaches is that it is difficult to guarantee high availability and they may not be viable options for your application. In fact, you would lose all of the advantages that the container provides by hand-coding proprietary solutions such as the ones outlined here, including automated passivation and robust, transparent state maintenance. Third, you may choose to maintain session state in the web container if you re building a web application. Although HTTP is a stateless protocol, the Java Servlet API provides the ability to maintain state by using the HttpSession object. The servlet container does not have to do heavy lifting like passivation and activation, and may perform better in certain situations. Be aware that too much data in the HttpSession could decrease performance of the servlet container as well, so this is not a silver bullet either. Moreover, you cannot use this option with thick or Java SE clients.
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Building business logic with session beans
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So when you need to maintain state in your applications and your clients are Java SE clients, then the first two options we discussed earlier may be more difficult to implement. Hence, stateful session beans are probably the only viable option as long as you carefully weigh the performance considerations we outlined earlier. We ll close our discussion on session beans by outlining some best practices for session beans that you can use to build your application s business logic.
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3.6 Session bean best practices
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In this section we outline some of the best practices for session beans that you can use while building the business logic tier for your application. Choose your bean type carefully. Stateless session beans will be suitable most of the time. Carefully examine whether your application needs stateful session beans, because it comes with a price. If the EJB client lies in the web tier, then using HttpSession may be a better choice than stateful session beans under some circumstances. Carefully examine interface types for session beans. Remote interfaces involve network access and may slow down your applications. If the client will always be used within the same JVM as the bean, then use a local interface. If you are using DI, make sure you don t inject a stateful session bean into a stateless session bean or servlet. Injected EJB instances are stored in an instance variable and are available globally for subsequent clients even if a stateless bean instance is returned to the pool, and an injected stateful bean instance may contain inaccurate state information that will be available to a different client. It s legal to inject a stateful bean instance to another stateful session bean or an application client. 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. 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. Don t forget to define remove methods in a stateful session bean. Tune passivation and timeout configurations to find the optimal values for your application.
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Summary
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3.7 Summary
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In this chapter, we examined the various session bean types and how stateless session beans and stateful session beans differ. We looked at the programming rules for both stateless and stateful session beans, and you saw comprehensive examples of both bean types. As you learned, stateless session beans have a simple lifecycle and can be pooled. Stateful beans require instances for each client, and for that reason they can consume a lot of resources. In addition, passivation and activation of stateful beans can impact performance if used inappropriately. You learned about alternatives for using stateful session beans, and that session bean clients can be either local or remote. We showed you that dependency injection simplifies the use of EJB and saves you from having to perform complex JNDI lookups. Finally, we provided some best practices for developing session beans. At this point you have all the ammunition necessary to build the business logic of your application using stateless and stateful session beans. In the next chapter we ll discuss how you can build messaging applications with messagedriven beans.
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