Web server extensions - Introduction to Entity Beans 123 Bank account
Introduction to Entity Beans 123 Bank account information, such as account number and balance Human resources data, such as names, departments, and salaries of employees Lead tracking information, such as names, addresses, and phone numbers of prospective customers that you want to keep track of over time Note that these components represent people, places, and things (they re nouns). They are well suited to handling business data. The big difference between session beans and entity beans is that entity beans have an identity and client-visible state, and that their lifetime may be completely independent of the client application s lifetime. For entity beans, having an identity means that different entity beans can be distinguished by comparing their identities. It also means that clients can refer to individual entity bean instances by using that identity, pass handles to other applications, and actually share common entities with other clients. All this is not possible with session beans. You might question the need for such persistent data components. Why should we deal with our business data as objects, rather than deal with raw database data, such as relational rows? It is handy to treat data as objects because they can be easily handled and managed and because they are represented in a compact manner. We can group related data in a unified object. We associate some simple methods with that data, such as compression or other data-related activities. We can also use implicit middleware services from an application server, such as relationships, transactions, network accessibility, and security. We can also cache that data for performance. Entity beans are these persistent data components. Entity beans are enterprise beans that know how to persist themselves permanently to a durable storage, such as a database or legacy system. They are physical, storable parts of an enterprise. Entity beans store data as fields, such as bank account numbers and bank account balances. They also have methods associated with them, such as getBankAccountNumber() and getAccountBalance(). For a full discussion of when to (and when not to) use entity beans, see Chapter 16. In some ways, entity beans are analogous to serializable Java objects. Serializable objects can be rendered into a bit-blob and then saved into a persistent store; entity beans can persist themselves in many ways, including Java serialization, O/R mapping, or even an object database persistence. Nothing in the EJB 2.x specification dictates any particular persistence mechanism, although O/R mappings are the most frequently used mechanism in practice. Entity beans are different from session beans. Session beans model a process or workflow (actions that are started by the user and that go away when the user goes away). Entity beans, on the other hand, contain core business data product information, bank accounts, orders, lead tracking information,
The UK has been a member of the European Union since 1973. The attitude of the present government towards further integration is conservative, with the official opposition favoring a return of some powers and competencies to the UK.From our experience, we can recommend Cheap UK Web Hosting services.