1. 6/19/20151

2. 2 Enterprise Java Beans Introduction –Application ServerApplication Server –Java 2 Enterprise EditionJava 2 Enterprise Edition What is an Enterprise Bean ? –EJB PropertiesEJB Properties –EJB OverviewEJB Overview –Deployment PhaseDeployment Phase –Type of beansType of beans Client access with interfaces –Remote accessRemote access –Local AccessLocal Access

3. 6/19/20153 Enterprise Java Beans Contents of an Enterprise Bean EJB Example EJB vs MTS A few EJB implementationsA few EJB implementations What’s new in EJB 2.0 Bibliography

4. 6/19/20154 Introduction Enterprise Java Beans ( EJB ) is –a middleware component model for Java and CORBA –a specification for creating server-side, scalable, transactional, multi-user and secure enterprise- level applications Presented by Sun in the 1999, they are easier than other technologies as RMI or Corba

5. 6/19/20155 Introduction This is the three level structure for Application Server

6. 6/19/20156 Applicaton Server Presentation –HTML Application –Java Application Business Logic Data Access

7. 6/19/20157 Presentation HTML –Generated server- side HTML –Runs on any Web browser –Less client-side power Java –Required Java virtual Machine –More client side power –Runned on a page –Launched from a browser or a standalone application

8. 6/19/20158 Business Logic Implements the logic of the application defining all the function that may be used from a client –Change Business Rules Easily –Re-use components –Make complex applications manageable

9. 6/19/20159 Data Access Utility to access external datas such as Database or other Web component

10. 6/19/201510 J2EE Application Server Java 2 Enterprise Edition standardizes interfaces for Application Server components

11. 6/19/201511 What is an Enterprise Bean ? Is a server side component written in Java Language Industry standard distribuited component model Incorporates the business logic of an application ( the code that implements the purpose of the application)

12. 6/19/201512 EJB Properties Bean writers need not write –Remote access Protocols –Transactional Behaviour –Threads –Security –State Management –Object life cycle –Resource pooling –Persistence

13. 6/19/201513 EJB Overview

14. 6/19/201514 Deployment Phase

15. 6/19/201515 Deployment Phase

16. 6/19/201516 When to use Enterprise bean The application must be scalable.It will run on different machine and their location will remain transparent to the client Transaction requirement The application will have lot of different type of clients

17. 6/19/201517 Type of beans Session Bean Entity Bean Message Driven Bean

18. 6/19/201518 Session Bean Represents a single client inside the server The client calls the session bean to invoke methods of an application on the server Perform works for its client, hiding the complexity of interaction with other objects in the server Is not shared Is not persistent When the client stops the session,the bean can be assigned to another client from the server

19. 6/19/201519 Session Bean Stateful session bean Stateless session bean

20. 6/19/201520 Stateful Session Bean Contains the state of a single client session: –Information on the client –On method called –Return values This state is called conversational state and is not retained when the session ends, also if the client not removes the bean

21. 6/19/201521 Stateless Session Bean Not maintain a conversational state for a particular client Contains values only for the duration of the single invocation Except during method invocation, all instances of stateless session bean are equivalent

22. 6/19/201522 Entity Bean Represents a business object in a persistent storage mechanism such as a relational database Usually is a table in the database and each instance of that entity bean is a row in that table Properties: PersistentPersistent Allow shared accessAllow shared access Have primary keyHave primary key Have relationship with other entity beans.Have relationship with other entity beans.

23. 6/19/201523 Entity Bean persistent Bean managed persistence Container managed persistence

24. 6/19/201524 Bean managed persistence Who write the bean’s code must access the database and save his own data

25. 6/19/201525 Container managed persistence The container save the data There is no code in the bean for access the database The container handles all database access required for the bean Links between beans are created using a structure called abstract schemaabstract schema

26. 6/19/201526 Entity bean’s shared access Entity beans can be used by different clients It’s important that they work whithin transactions The EJB container provides transaction management The transaction’s attribute are specified in the bean’s deployment description

27. 6/19/201527 Entity bean’s primary key Each entity bean has a unique object identifier like a key in a database table

28. 6/19/201528 Entity bean’s relationship Container managed persistent –The container performs all the operation to create relationship Bean managed persistent –The code to perform relations must be written in the bean

29. 6/19/201529 Message Driven bean Allows applications to process messages asynchronously The messages may be sent by : –An application client –Another enterprise bean –A Web component

30. 6/19/201530 Message Driven bean Retain no data or conversational state for a specific client All instances are equivalent, allowing the EJB container to assign a message to any message-driven bean instance. The container can pool these instances to allow streams of messages to be processed concurrently Can process messages from multiple clients

31. 6/19/201531 Message Driven bean A client can’t access directly to a message driven bean When a message arrive, the container gives it to a message driven bean The bean process the message

32. 6/19/201532 Client access with interfaces A client may access a session or an entity bean only through the methods defined in the bean's interfaces They define the client's view of a bean Types of access: –Remote access –Local access

33. 6/19/201533 Remote access A remote client of an enterprise bean has the following traits: –It may run on a different machine and a different Java virtual machine than the enterprise bean it accesses (It is not required to run on a different JVM ) –It can be a Web component –It can be another enterprise bean

34. 6/19/201534 Remote access To create an enterprise bean with remote access, you must : –Code a remote interface Business methods –Code a home interface Finder methods Home methods

35. 6/19/201535 Remote access example

36. 6/19/201536 Local access A local client has these characteristics –It must run in the same JVM as the enterprise bean it accesses –It may be a Web component or another enterprise bean –To the local client, the location of the enterprise bean it accesses is not transparent –It is often an entity bean that has a container- managed relationship with another entity bean

37. 6/19/201537 Local access To create an enterprise bean with local access, you must : –Code the local interface Bean's business methods –Code the local home interface Life cycle Finder methods

38. 6/19/201538 Local interfaces If an entity bean is the target of a container managed relationship it MUST have local interfaces

39. 6/19/201539 Contents of an Enterprise Bean Deployment descriptor –Persistence type –Transaction attribute Enterprise bean class Interfaces Helper classes –Exception –Utility classes

40. 6/19/201540 EJB Example The OnLine Bank We will take a not completed system to give an idea to how choose if a component is an entity, session or message driven bean.

41. 6/19/201541 EJB Example Virtual Bank Client SecurityAccounts Services

42. 6/19/201542 EJB Example The example has three component: –Services: what the client can do in the system such as see the foreign currency, listed shares or make operations on his hown account. –Accounts: a database containing the accounts of all the clients of the bank with information about credit,debit,access etc.. –Security: is a subsystem that receives all the alarm caused from wrong access and performs action about the situation ( calls police and stops operation of that client keeping information about him )

43. 6/19/201543 EJB Example In this example is easy to create an EJB structure. –Client will have a web page at client side to insert values and connect the system.This will be done using JSP ( Java Servlet Pages ) –Services will be a Statefull Session Bean and it will be different for each client connecting the system mantaining data about the client connected. –Accounts will be formed by an Entity Bean for each account in the system with a code-account as primary key. –Security will be a Message driven bean and will be called only from container if some operation are abnormal for result or the autentification for the same client fails too much times.

44. 6/19/201544 EJB vs MTS Microsoft Transaction Server is based on the Component Object Model (COM) which is the middleware component model for Windows NT MTS can be defined as a component-based programming model

45. 6/19/201545 EJB vs MTS Analogies Implement business logic for Application Server components Have a Server and a container ( for MTS called MTS Executive ) Similar architecture in both modelsboth models A client invokes wrapped method

46. 6/19/201546 EJB vs MTS Difference EJB –Component instance are pooled –Don’t support heterogeneous transactions –Portability accross multiple platforms using Java platform MTS –Component is not created until the call from a client reaches the container –Support heterogeneous transactions –Portability only on Windows NT

47. 6/19/201547 EJB vs MTS Difference EJB –Invoked by clients using RMI –Has both persistent and non-persistent components MTS –Invoked by clients using DCOM or through local COM calls –Components are not persistent, even though they may contain information

48. 6/19/201548 A few EJB implementations WebLogic Bluestone Novera Persistence Oracle AS Oracle8i

49. 6/19/201549 What’s new in EJB 2.0 Released On April 26, 2001 Integration with Java TM Message Service (JMS) -- Asynchronous Capabilities Streamline Systems –Send asynchronous messages via the JMS API Container-Managed Persistence (CMP) -- Simplifying and Expediting Application Development –Used to isolate the application developer from the physical database schema –Introduces for the first time a portable query language, based on the abstract schema

50. 6/19/201550 What’s new in EJB 2.0 Local Interfaces -- Streamlining Calls Between Local Beans –The local interface may be defined for a bean during development, to allow streamlined calls to the bean if a caller is in the same container Inter-Server Interoperability -- Enabling Heterogeneous Environments –Takes the benefit of cross-server application portability –Able to deploy the EJB technology-based application across a heterogeneous environment mixing application servers from different vendors

51. 6/19/201551 Bibliography The J2EE Tutorial –http://java.sun.com/j2ee/tutorial/1_3- fcs/doc/EJBConcepts.htmlhttp://java.sun.com/j2ee/tutorial/1_3- fcs/doc/EJBConcepts.html Meeting about Application servers –http://www.phxjug.org/meetings/silverstream/sld001.htmhttp://www.phxjug.org/meetings/silverstream/sld001.htm Developing Enterprise components –http://spectral.mscs.mu.edu/EJB20001113/index.htmlhttp://spectral.mscs.mu.edu/EJB20001113/index.html A detailed Comparison of EJB & MTS models –http://members.tripod.com/gsraj/misc/ejbmts/ejbmtscomp.ht mlhttp://members.tripod.com/gsraj/misc/ejbmts/ejbmtscomp.ht ml

52. 6/19/201552 Bibliography What's new in the Enterprise JavaBeans TM 2.0 Specification? –http://java.sun.com/products/ejb/2.0.htmlhttp://java.sun.com/products/ejb/2.0.html Introduction to Enterprise JavaBeans –http://cosmos.inesc.pt/~a01/javacourses/ejb/http://cosmos.inesc.pt/~a01/javacourses/ejb/ Programming WebLogic Enterprise JavaBeans –http://e-docs.bea.com/wls/docs61/ejb/index.htmlhttp://e-docs.bea.com/wls/docs61/ejb/index.html

53. 6/19/201553 The MTS architecture Is made up of: –The MTS Executive (mtxex.dll) –The Factory Wrappers and Context Wrappers for each component –The MTS Server Component –MTS clients –Auxiliary systems like COM runtime services, Service Control Manager (SCM) The Microsoft Distributed Transaction Coordinator (MS- DTC) The Microsoft Message Queue (MSMQ) The COM-Transaction Integrator (COM-TI)

54. 6/19/201554 The MTS architecture

55. 6/19/201555 The EJB architecture Consists of: –An EJB server –EJB containers that run within the server –Home objects –Remote EJBObjects –Enterprise Beans –EJB clients –Auxiliary systems like Java Naming and Directory Interface (JNDI) Java Transaction Service (JTS) Security services

56. 6/19/201556 The EJB architecture

57. 6/19/201557 Stateful session bean’s life cycle The client invoke the create method The EJB container : –Instantiates the bean –Invokes the setSessionContext –Invokes ejbCreate The bean is ready

58. 6/19/201558 Stateful session bean’s life cycle While in the ready state –EJB container may passivate the bean moving it from memory to secondary storage –A client may invoke a business method –EJB container may activate a bean,moving it back to the ready stage, and then calls the bean's ejbActivate method –A client may invoke the remove method and the container calls the bean's ejbRemove method

59. 6/19/201559 Stateful session bean’s life cycle

60. 6/19/201560 Stateless session bean’s life cycle The client invoke the create method The EJB container : –Instantiates the bean –Invokes the setSessionContext –Invokes ejbCreate The bean is ready

61. 6/19/201561 Stateless session bean’s life cycle While in the ready state –A client may invoke a business method –A client may invoke the remove method and the container calls the bean's ejbRemove method –It’s never passivate

62. 6/19/201562 Stateless session bean’s life cycle

63. 6/19/201563 Entity bean’s life cycle The EJB container : –Creates the instance –Calls the setEntityContext The entity bean moves to a pool of available instances

64. 6/19/201564 Entity bean’s life cycle While in the pool : –Instance is not associated with any particular object identity –All instances in the pool are identical –EJB container may assign an identity to an instance when moving it to the ready stage invoking the ejbActivate method –A client may invoke the create method EJB container calls ejbCreate and ejbPostCreate –EJB container may remove the instance invoking unsetEntityContext

65. 6/19/201565 Entity bean’s life cycle While in the ready state : –A client may invoke entity bean's business methods –A client may invoke the remove method EJB container calls the ejbRemove method –EJB container may invoke the ejbPassivate method

66. 6/19/201566 Entity bean’s life cycle

67. 6/19/201567 Message driven bean’s life cycle EJB container creates a pool of message- driven bean instances For each instance, the EJB container instantiates the bean : –It calls the setMessageDrivenContext –It calls the instance's ejbCreate Like a stateless session bean,it’s never passivated, It has only two states: –Nonexistent –Ready to receive messages.

68. 6/19/201568 Message driven bean’s life cycle While in the ready state : –EJB container may call onMessage –EJB container may call the ejbRemove

69. 6/19/201569 Message driven bean’s life cycle

70. 6/19/201570 Abstract schema Part of an entity bean's deployment descriptor Defines the bean's persistent fields and relationships.The term abstract distinguishes this schema from the physical schema of the underlying data store You specify the name of an abstract schema in the deployment descriptor

71. 6/19/201571 Example of Abstract schema

72. 6/19/201572 Abstract schema Persistent fields –Are stored in the underlying data store –Constitute the state of the bean. At runtime, the EJB container automatically synchronizes this state with the database –During deployment, the container Maps the entity bean to a database table Maps the persistent fields to the table's columns

73. 6/19/201573 Abstract schema Relationship fields –It’s like a foreign key in a database table.It identifies a related bean –Like a persistent field, a relationship field is virtual and is defined in the enterprise bean class with access methods –Unlike a persistent field, a relationship field does not represent the bean's state

74. 6/19/201574 Abstract schema Multiplicity in Container-Managed Relationships –One-to-one: Each entity bean instance is related to a single instance of another entity bean –One-to-many: An entity bean instance may be related to multiple instances of the other entity bean –Many-to-one: Multiple instances of an entity bean may be related to a single instance of the other entity bean –Many-to-many: The entity bean instances may be related to multiple instances of each other

75. 6/19/201575 Abstract schema Direction in Container-Managed Relationships –Bidirectional relationship: each entity bean has a relationship field that refers to the other bean. Through the relationship field, an entity bean's code can access its related object –Unidirectional relationship: only one entity bean has a relationship field that refers to the other

76. 6/19/201576 EJB 3.0 This section based on Mastering EJB 3.0 4 th Ed

77. 6/19/201577 EJB 3.0 Key issues for distributed systems –Remote Method Invocation –Load Balancing –Transparent failover –Back-end integration to legacy systems –Transactions –Clustering (state replication across servers) –Dynamic redeployment (upgrade while running)

78. 6/19/201578 EJB 3.0 More key issues –Clean shutdown –Logging & auditing –Systems management –Threading –Message-oriented middleware –Component lifecycle –Resource pooling

79. 6/19/201579 EJB 3.0 Yet more issues –Security –Caching –Etc., etc.

80. 6/19/201580 EJB 3.0 All of these can be thought of as middleware services Developer of distributed app shouldn’t have to worry about them –Should concentrate on business logic –Much too expensive to build from scratch –Distributed app should be portable across middleware service providers

81. 6/19/201581 EJB 3.0 EJB spec defines standard interfaces between distributed components & their containers

82. 6/19/201582 EJB 3.0 Advantages –Industry standard Vendors design containers to EJB specs –Portability possible across containers –RAD capable because services provided by container

83. 6/19/201583 EJB 3.0 What’s an EJB? –Server-side component encapsulating application functionality Business logic DB access Integrate with other legacy systems Serve multiple clients –Browser –Desktop apps –Other EJBs –Web app components (e.g., Servlets) –Web Service clients

84. 6/19/201584 EJB 3.0 How do they work? –EJB can be located anywhere, usually on another machine –Use RMI-IIOP for remote invocation of methods (P. 15) –Location transparency Client thinks remot EJB is local –Run inside EJB container Application servers

85. 6/19/201585 EJB 3.0 Who makes containers? –Most of the usual enterprise suspects BEA, IBM, Red Hat (JBOSS), Sun, Oracle Closely related to web services –P. 29

86. 6/19/201586 EJB 3.0 EJB 2.1 was NASTY!! –HelloWorld EJB 2.1 (pp. 40-49) –Many disappointed enterprise developers Vastly simplified in EJB 3.0 –HelloWorld EJB 3.0 (pp. 83-85) –Many ‘once burned twice shy’ developers Sun’s dilemma: –‘If we simplify it, will they resume coding EJBs?’

87. 6/19/201587 EJB 3.0 EJB best practices For appropriate use only –Remoting is required –Distributed transactions required –Component security required –Persistence required –Legacy system integration –Scalability required

88. 6/19/201588 EJB 3.0 If your application components don’t need to be distributed across servers, avoid using distributed components like EJBs

89. 6/19/201589 EJB 3.0 This section based on: J2EE Development Without EJB

90. 6/19/201590 EJB 3.0 Written by a ‘once burned twice shy’ EJB developer Observations apply to EJB 2.1 (and earlier) experiences –EJB 3.0 spec in early stages when book written

91. 6/19/201591 EJB 3.0 Basic thesis is EJBs…. –Rarely necessary for web-based applications –Commonly overused –Symptom of over-engineering –Can obtain most of needed EJB services via other programming techniques using lightweight containers (e.g., Spring) Java EE & Java SE Aspect-oriented programming Dynamic proxies

92. 6/19/201592 EJB 3.0 He’s not alone Many other enterprise architects and developers have critized EJBs since early 2000s Martin Fowler’s Law of Distributed Objects ‘Don’t do it!!’

93. 6/19/201593 EJB 3.0 Some criticisms –Too complex Specifications getting more complex EJB 3.0 tries to address this –Unit testing hard to do Have to isolate app from container If something broken, is it container related or app related?

94. 6/19/201594 EJB 3.0 –Other technologies (AOP) get the job done more easily –Entity beans are a flop EJB 3.0 doesn’t upgrade entity beans Left to wither on the Java EE vine Persistence API tries to address this

95. 6/19/201595 EJB 3.0 Metadata (a la.NET) are better than descriptor files –Annotations designed to address this Only truly unique service provided by EJB is remote access to a component Java EE provides other services already –JNDI, JTA, JCA, resource pooling, etc.

96. 6/19/201596 EJB 3.0 EJBs remain best choice for apps that genuinely need object distribution or use IIOP protocol EJBs also pretty good for apps based around asynchronous messaging –Message-drive beans pretty simple

97. 6/19/201597 EJB 3.0 Financial services middleware likely good place for EJB-driven apps Argues that EJBs are declining technology & will be legacy within 3 years Doesn’t think EJB 3.0 will make much of a difference

98. 6/19/201598 EJB 3.0 Advocates use of lightweight containers like Spring…. Oh btw, author is co-founder of Spring framework! Bias is always an issue!

99. 6/19/201599 EJB 3.0 What’s an enterprise developer to do? Distributed systems a holy grail of system architecture & deployment since early 90s –CORBA initiative began in 91 –Web Services are current frontier IT profession still learning when & how to do distributed systems

100. 6/19/2015100 EJB 3.0 References Master Enterprise JavaBeans 3.0, 4 th Ed, Sriganesh et. Al., 2006 J2EE Development Without EJB, Johnson, 2004