how to generate barcode in vb.net 2008 Referencing session beans from helper classes in Java

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12.2.2 Referencing session beans from helper classes
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Sometimes you ll find that you need to access a session bean from a class that is not managed. Dependency injection is not supported in nonmanaged classes. For example, your JSF managed bean may be using some utility classes that are not managed by the container. You cannot inject an instance of an EJB into those classes. Again, in this case you must use JNDI lookup to access your session bean. This method is also used by managed classes when you want to avoid injection. For looking up an EJB from a helper class you have to do the following:
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Accessing session beans from the web tier
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Establish the reference to EJB by using the @EJB annotation at the class level or the ejb-ref (ejb-local-ref) descriptor element. Look up the session bean.
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Remember from our discussion in part 2 of this book that the @EJB annotation can be used for injecting session bean references to a field or a setter method or can be applied at the class level to establish a reference that can be used with JNDI lookup. The class where you use the @EJB annotation should be the managed class that uses a helper class. For example, say you have a helper class named BidProcessor that is used by ActionBazaarBidControllerServlet. The BidProcessor class looks up the PlaceBid EJB. You cannot use the @EJB annotation with the BidProcessor class because it is not a managed class. Here the entry point for the BidProcessor class is ActionBazaarBidControllerServlet, and that s the reason we can use the @EJB annotation as follows:
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@EJB (name = "ejb/PlaceBid", beanInterface = PlaceBid.class) public class ActionBazaarBidControllerServlet extends HttpServlet { }
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Then look up the EJB in the helper class (BidProcessor) like this:
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PlaceBid placeBid = (PlaceBid)context.lookup("java:comp/env/ejb/PlaceBid"); placeBid.addBid(bidderId, itemId, bidPrice);
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In other cases the entry point of your web framework may be a managed class, but you may not be able to modify the code in a way that allows you to use an annotation to establish EJB references. For example, if you are using a framework such as Struts, the entry point for your application is the controller class in the framework, and modifying such frameworks to establish EJB references may not be part of your project. In this case you can use the ejb-ref element in web.xml to establish the EJB references so that the EJBs being used will be bound to the JNDI tree, and thereby visible to your classes via JNDI lookup. Using the global JNDI name With some application servers, you may be able to work around specifying references using the @EJB annotation or the web.xml descriptor element by using the global JNDI name. Recall from our discussion earlier that many vendors allow EJB access using global JNDI names, such as the EJB name or by using an EJB class name without having to specify the ejb-ref or ejb-local-ref.
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Effectively integrating EJB 3 across your application tiers
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For example, some application servers will allow the lookup of an EJB as follows:
PlaceBid placeBid = (PlaceBid)context.lookup("PlaceBid");
while others may allow the following type of lookup:
PlaceBid placeBid = (PlaceBid)context.lookup("actionbazaar.buslogic.PlaceBid");
Keep in mind that these approaches are not portable across containers and we recommend you use an EJB reference during lookup.
JNDI and Service Locator design pattern
If you have used EJB 2 or J2EE 1, then you are probably very familiar with service locators. If you haven t used them, take a look at http://java.sun.com/blueprints/ corej2eepatterns/Patterns/ServiceLocator.html. Simply put, the Service Locator design pattern is used to abstract the complexities of JNDI by helping reduce repetitive JNDI code, enforcing a single point of control for lookup, and improving performance of EJB lookups with caching. Many developers believe that the Service Locator pattern will no longer be used with EJB 3 due to dependency injection taking a front-row seat. However, the reality is that EJB 3 dependency injection is not supported in all circumstances and you may still need to rely on good ol JNDI lookup. Therefore, service locators may not be dead just yet. There are alternatives to using the Service Locator pattern and JNDI for using resources or EJBs. One such alternative is injecting a bean instance in the managed class and passing it to the helper class as a parameter to its constructor. For example, the BidManager EJB uses a helper class, BidManagerHelper, that invokes a method in the ItemManager EJB. BidManagerHelper is a regular POJO, so we cannot inject the ItemManager instance. However, we can inject the ItemManager EJB into BidManagerEJB and pass it to the helper class as follows:
@Stateless public class BidManagerBean implements BidManager { @EJB ItemManagerLocal itemManager; public Bid placeBid() { BidManagerHelper helper = new BidManagerHelper (itemManager); ... } }
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