Web hosts - Introduction to Session Beans 81 Another example of
Introduction to Session Beans 81 Another example of a drawn-out business process is a banking application. You may have code representing a bank teller who deals with a particular client for a long period of time. That teller may perform a number of banking transactions on behalf of the client, such as checking the account balance, depositing funds, and making a withdrawal. A stateful session bean is a bean that is designed to service business processes that span multiple method requests or transactions. To accomplish this, stateful session beans retain state on behalf of an individual client. If a stateful session bean s state is changed during a method invocation, that same state will be available to that same client upon the following invocation. Stateless Session Beans Some business processes naturally lend themselves to a single request conversation. A single request business process is one that does not require state to be maintained across method invocations. A stateless session bean is a bean that holds conversations that span a single method call. They are stateless because they do not hold multimethod conversations with their clients. After each method call, the container may choose to destroy a stateless session bean, or recreate it, clearing itself out of all information pertaining to past invocations. It also may choose to keep your instance around, perhaps reusing it for all clients who want to use the same session bean class. The exact algorithm is container specific. The takeaway point is this: Expect your bean to forget everything after each method call, and thus retain no conversational state from method to method. If your bean happens to hang around longer, then great but that s your container s decision, and you shouldn t rely on it. For a stateless session bean to be useful to a client, the client must pass all client data that the bean needs as parameters to business logic methods. Alternatively, the bean can retrieve the data it needs from an external source, such as a database. Stateless really means no conversational state. Stateless session beans can contain state that is not specific to any one client, such as a database connection factory that all clients would use. You can keep this around in a private variable. So long as you re willing to lose the data in your private variable at any time, you ll be fine. An example of a stateless session bean is a high-performance engine that solves complex mathematical operations on a given input, such as compression of audio or video data. The client could pass in a buffer of uncompressed data, as well as a compression factor. The bean returns a compressed buffer and is
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