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EJB Fundamentals

EJB Fundamentals. Swapnil Shrivastava. Contents. Introduction Technology Overview EJB Architecture EJB Specification Sample Application. Sun’s Definition.

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EJB Fundamentals

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  1. EJB Fundamentals Swapnil Shrivastava

  2. Contents • Introduction • Technology Overview • EJB Architecture • EJB Specification • Sample Application (c)CDAC(Formerly NCST)

  3. Sun’s Definition • EJB architecture is a component architecture for the development and deployment of component based distributed business applications. • Applications written using EJB architecture are scalable, transactional, and multi-user secure. • These applications may be write once, and then deployed on any server platform that supports the EJB specification. (c)CDAC(Formerly NCST)

  4. Short Definition • EJB is a server-side component architecture that simplifies the process of building enterprise-class distributed component applications in Java. • EJB provides standard for component architecture. (c)CDAC(Formerly NCST)

  5. Enterprise Bean • Server side software components that can be deployed in distributed multi tier environment. • They encapsulate business logic of an application. • Consists of one or more java objects. (c)CDAC(Formerly NCST)

  6. Types of Beans • Session Bean • Entity Bean • Message driven Bean (c)CDAC(Formerly NCST)

  7. Session Bean • Session beans model business processes. • They are like ‘verbs’ because they are actions. • E.g. billing engine, catalog engine etc: (c)CDAC(Formerly NCST)

  8. Entity Bean • Entity Bean Models business data. • They are like ‘nouns’ because they are data objects • E.g. product, an order, an employee etc: • Session beans typically calls entity beans to perform business goals. (c)CDAC(Formerly NCST)

  9. Message Driven Bean • Message driven beans are similar to session beans. • They are actions. • They are called only when they receive some message. • E.g. : stock trade message. (c)CDAC(Formerly NCST)

  10. EJB Architecture HTML Client Business Partner System Presentation Tier HTTP SOAP,UDDI WSDL,ebXML Firewall Messaging Client C/C++ Client Java Applet Java Appl Servlet JSP Web Server CORBA-IIOP RMI-IIOP RMI-IIOP RMI-IIOP Messaging Application Server EJB Message Driven Bean EJB Session Bean EJB Session Bean Business Tier EJB Session Bean EJB Entity Bean EJB Session Bean (c)CDAC(Formerly NCST)

  11. EJB Foundation: Distributed Objects Client Distributed Object Remote Interface Remote Interface Skeleton Stub Network (c)CDAC(Formerly NCST)

  12. What do we need to worry about now? We take a monolithic application and break it into distributed system with multiple clients connecting to multiple servers and databases over network. (c)CDAC(Formerly NCST)

  13. Remote Method Invocation Load Balancing Transparent Fail Over Back end integration. Clustering Dynamic Re deployment Object life cycle Caching Security Resource Pooling System Management Message Oriented Middleware And many more….. Services Middleware (c)CDAC(Formerly NCST)

  14. Explicit Middleware Transaction API Transaction Services Security API Client Distributed Object Security Services Remote Interface Database API Remote Interface Database drivers Skeleton Stub Network (c)CDAC(Formerly NCST)

  15. Example – Bank account obj • Transfer(Acct acc1, Acct acc2,long amt) //1.Call middleware API to perform security check. //2.Call middleware API to start a trans //3.Call middleware API to load rows from db. //4.perform trans. //5.Call middleware API to store rows in db //6.Call middleware API to end the trans. (c)CDAC(Formerly NCST)

  16. Explicit Middleware • Difficult to Write. • Difficult to Maintain. • Difficult to Support. (c)CDAC(Formerly NCST)

  17. Implicit Middleware Distributed Object Client Transaction API Remote Interface Transaction Services Security API Request Interceptor Security Services Remote Interface Remote Interface Database API Database drivers Skeleton Stub Network (c)CDAC(Formerly NCST)

  18. Example – Bank account obj • Transfer(Acct acc1,Acct acc2,long amt) //1. Perform trans.(subtract bal from one account and add to other). (c)CDAC(Formerly NCST)

  19. Implicit Middleware • Easy to Write. • Easy to Maintain. • Easy to Support. (c)CDAC(Formerly NCST)

  20. EJB Container • House enterprise bean and makes them available to the client to invoke them remotely. • It intercepts the client request and delegates them to corresponding bean class. • It automatically performs implicit middleware that the distributed object needs. • EJB object is the physical part of the container. (c)CDAC(Formerly NCST)

  21. EJB Component Ingredients • Enterprise Bean Class • Interfaces • Remote and Home interface for remote access. • Local and Local Home interface for local access. • Deployment Descriptor. • Vendor Specific files. (c)CDAC(Formerly NCST)

  22. Enterprise Bean Class • It conforms to a well defined interface. • It contains business implementation details of our component. • Each bean type has more specific interface that extends javax.ejb.EnterpriseBean interface. • Bean class implements the interface corresponding to the bean type. (c)CDAC(Formerly NCST)

  23. EJB Object • Client request interceptor. • It duplicates all the business logic methods that the corresponding bean class exposes. • Proprietary and specific to each EJB container. (c)CDAC(Formerly NCST)

  24. Remote Interface • Interface to request interceptor. • Informs EJB Object auto generator which methods to clone. • All remote interfaces must derive from javax.ejb.EJBObject. • EJB remote interfaces must confirm to RMI rules. (c)CDAC(Formerly NCST)

  25. Home Object • EJB object factory. • Creates,finds and destroys EJB objects. • Proprietary and specific to each EJB container. • Home objects implements Home Interface. (c)CDAC(Formerly NCST)

  26. Home Interface • EJB Object factory interface. • They define methods for creating,destroying and finding EJB Objects. • All home interfaces must extend javax.ejb.EJBHome. • EJB remote interfaces must confirm to RMI rules. (c)CDAC(Formerly NCST)

  27. Local Access • Local objects make enterprise bean calls fast and efficient. • Local objects implements Local Interface. • Local home objects creates beans fast. • Local home object implemnts Local Home interface. (c)CDAC(Formerly NCST)

  28. Deployment Descriptor • Declare how the container should perform middleware services for the EJB component. • In EJB 2.0 deployment descriptor is a XML file. • Key to implicit middleware. (c)CDAC(Formerly NCST)

  29. Vendor Specific Files • All vendors have proprietary value added features. • Include files specific to that vendor. (c)CDAC(Formerly NCST)

  30. Package Remote Interface Local Interface EJB jar file Jar file creator Enterprise Bean Home Interface Deployment Descriptor Vendor Specific (c)CDAC(Formerly NCST)

  31. Sample ApplicationMy First Bean! (c)CDAC(Formerly NCST)

  32. Session Bean : FirstBean package example; public class FirstBean implements javax.ejb.SessionBean { private SessionContext ctx; public void ejbCreate() { System.out.println(“ejbCreate()”); } public void ejbRemove() { System.out.println(“ejbRemove()”); } public void ejbActivate() { System.out.println(“ejbActivate()”); } (c)CDAC(Formerly NCST)

  33. public void ejbPassivate() { System.out.println(“ejbPassivate()”); } public void setSessionContext(javax.ejb.SessionContext ctx) { this.ctx=ctx; } public String first() { System.out.println(“first()”); return “My First Bean”; } } (c)CDAC(Formerly NCST)

  34. Remote Interface : First.java package example; public interface First extends javax.ejb.EJBObject { public String first() throws java.rmi.RemoteException; } (c)CDAC(Formerly NCST)

  35. Home Interface : FirstHome package example; public interface FirstHome extends javax.ejb.EJBHome { First create() throws java.rmi.RemoteException, javax.ejb.CreateException; } (c)CDAC(Formerly NCST)

  36. Deployment Descriptor <ejb-jar> <enterprise-bean> <session> <ejb-name>First</ejb-name> <home>example.FirstHome</home> <remote>example.First</remote> <ejb-class>example.FirstBean<ejb-class> <session-type>Stateless</session-type> <transaction-type>Container</transaction-type> </session> </enterprise-bean> </ejb-jar> (c)CDAC(Formerly NCST)

  37. Client Application package example; import javax.naming.*; Import java.util.*; public class FirstClient { public static void main(String[] arg) throws Exception { Properties props=System.getProperties(); Context ctx=new InitialContext(props); Object obj=ctx.llokup(“FirstHome”); FisrtHome home=(FirstHome) javax.rmi.RemotePortableObject.narrow (obj,FirstHome.class); (c)CDAC(Formerly NCST)

  38. First first=home.create(); System.out.println(first.first()); first.remove(); } } (c)CDAC(Formerly NCST)

  39. EJB Object Model <<interface>> java.rmi.Remote <<interface>> java.io.Serializable Comes with Java2 platform <<interface>> javax.ejb.EJBObject <<interface>> Javax.ejb.EJBHome <<interface>> javax.ejb.EnterpriseBean <<interface>> javax.ejb.SessionBean Comes with EJB Distribution <<interface>> Remote Interface <<interface>> Home Interface Bean Implement Class Written by developer EJB Object Home Object (c)CDAC(Formerly NCST) Generated by Componet Vendor Tool

  40. EJB Container 3: Create a new EJB Object Home Interface Client Home Object 5: Return EJB Object Reference 4: Create a new EJB Object 6: Invoke Business Method 2 : Return Home object Reference 1 : Retrieve Home object Reference EJB Object Enterprise Bean Remote Interface 7: Delegate Request to Bean JNDI Naming Service (c)CDAC(Formerly NCST)

  41. Advantages of EJB • Helps to write scalable,reliable and secure applications. • Provides distributed component framework and hence supports rapid application development. • Supports application portablility and reusability across any vendor’s enterprise middleware services. • It is agreed upon by industry. (c)CDAC(Formerly NCST)

  42. References • Mastering Enterprise Java Beans • J2EE 1.4 Tutorials • Professional Java Server Programming, J2EE Edition (c)CDAC(Formerly NCST)

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