how to generate barcode in vb.net 2008 Renaissance of EJB in Java

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Renaissance of EJB
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1.4.4 Dependency injection vs. JNDI lookup
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One of the most tedious parts of EJB 2 development was writing the same few lines of boilerplate code many times to do a JNDI lookup whenever you needed to access an EJB or a container-managed resource, such as a pooled database connection handle. In POJOs in Action, Chris Richardson sums it up well:
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A traditional J2EE application uses JNDI as the mechanism that one component uses to access another. For example, the presentation tier uses a JNDI lookup to obtain a reference to a session bean home interface. Similarly, an EJB uses JNDI to access the resources that it needs, such as a JDBC DataSource. The trouble with JNDI is that it couples application code to the application server, which makes development and testing more difficult.
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In EJB 3, JNDI lookups have been turned into simple configuration using metadata-based dependency injection (DI). For example, if you want to access the HelloUser EJB that we saw in listing 1.1 from another EJB or servlet, you could use code like this:
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... @EJB private HelloUser helloUser; void hello(){ helloUser.sayHello("Curious George"); } ...
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Isn t that great The @EJB annotation transparently injects the HelloUser EJB into the annotated variable. EJB 3 dependency injection essentially gives you a simple abstraction over a full-scale enterprise JNDI tree. Note you can still use JNDI lookups where they are unavoidable.
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1.4.5 Simplified persistence API
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A lot of the problems with the EJB 2 persistence model were due to the fact that it was applying the container paradigm to a problem for which it was ill suited. This made the EJB 2 entity bean programming model extremely complex and unintuitive. Enabling remote access was one of the prime motivators behind making entity beans container-managed. In reality, very few clients made use of this feature because of performance issues, opting to use session beans as the remote access point.
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What s what in EJB 3
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Undoubtedly entity beans were easily the worst part of EJB 2. EJB 3 solves the problem by using a more natural API paradigm centered on manipulating metadata-based POJOs through the EntityManager interface. Moreover, EJB 3 entities do not carry the unnecessary burden of remote access. Another limitation with EJB 2 was that you couldn t send an EJB 2 entity bean across the wire in different tiers. EJB developers discovered an anti-pattern for this problem: adding another layer of objects the data transfer objects (DTOs). Chris sums it up nicely:
You have to write data transfer objects A data transfer object (DTO) is a dumb data object that is returned by the EJB to its caller and contains the data the presentation tier will display to the user. It is often just a copy of the data from one or more entity beans, which cannot be passed to the presentation tier because they are permanently attached to the database. Implementing the DTOs and the code that creates them is one of the most tedious aspects of implementing an EJB.
Because they are POJOs, entities can be transferred between different tiers without having to resort to anti-patterns such as data transfer objects. The simplification of the persistence API leads to several other benefits, such as standardization of persistence frameworks, a separable persistence API that can be used outside EJB container, and better support of object-oriented features such as inheritance and polymorphism. We ll see EJB 3 persistence in action in chapter 2, but now let s take a close look at some of the main features of the persistence API. Standardized persistence One of the major problems with EJB 2 entity beans was that ORM was never standardized. EJB 2 entity beans left the details of database mapping configuration to the provider. This resulted in entity beans that were not portable across container implementations. The EJB 2 query mechanism, EJB -QL, had a similar unfinished feel to it. These standardization gaps have in effect given rise to highly divergent alternative ORM paradigms like Hibernate, Oracle TopLink, and JDO. A major goal of JPA is to close the standardization gaps left by EJB 2. EJB 3 solidifies automated persistence with JPA in three distinct ways. First, it provides a robust ORM configuration set capable of handling most automated persistence complexities. Second, the Java Persistence Query Language (JPQL) significantly improves upon EJB -QL, standardizing divergent OR query technologies. Third,
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