1. Enterprise Applications & Java/J2EE Technologies Dr. Douglas C. Schmidt d.schmidt@vanderbilt.edu http://www.dre.vanderbilt.edu/~schmidt/ Professor of EECS Vanderbilt University Nashville, Tennessee

2. Tutorial on J2EE Douglas C. Schmidt 2 Agenda What makes an application “Enterprise”? Java/J2EE to develop Enterprise Applications EJB Specification JBoss Application Server + AOP What is an Architect’s role?

3. Tutorial on J2EE Douglas C. Schmidt 3 Enterprise Architectures They all have well thought out solutions to the “-ilities” of software development.

4. Tutorial on J2EE Douglas C. Schmidt 4 Enterprise = “-ilities” Availability Dependability Distributability Maintainability Reusability Reliability Scalability Recoverability Etc…

5. Tutorial on J2EE Douglas C. Schmidt 5 Availability The accessibility of a system resource in a timely manner; for example, the measurement of a system's uptime.

6. Tutorial on J2EE Douglas C. Schmidt 6 Dependability "[..] the trustworthiness of a computing system which allows reliance to be justifiably placed on the service it delivers [..]" –IFIP WG10.4 on DEPENDABLE COMPUTING AND FAULT TOLERANCEIFIP WG10.4 on DEPENDABLE COMPUTING AND FAULT TOLERANCE

7. Tutorial on J2EE Douglas C. Schmidt 7 Distributability Involve Multiple Environments/Servers Can span across geographical locations Hand held devices to Multiprocessor Servers

8. Tutorial on J2EE Douglas C. Schmidt 8 Maintainability “You are developing tomorrow’s legacy code” To keep up or carry on; continue. To keep in a condition of good repair or efficiency. –What makes a system maintainable?

9. Tutorial on J2EE Douglas C. Schmidt 9 Reusability To use again, especially after salvaging or special treatment or processing. Reduces duplicate code / “Copy & Paste” Easier to maintain Faster to develop

10. Tutorial on J2EE Douglas C. Schmidt 10 Reliability The trustworthiness to do what the system is expected or designed to do. Available 24-7-365 Performs within acceptable thresholds

11. Tutorial on J2EE Douglas C. Schmidt 11 Scalability “Refers to how much a system can be expanded. The term by itself implies a positive capability. For example, "the device is known for its scalability" means that it can be made to serve a larger number of users without breaking down or requiring major changes in procedure.” –Computer Desktop Encyclopedia

12. Tutorial on J2EE Douglas C. Schmidt 12 Recoverability Single point of failure Clustered servers Emergency backup plans Disaster backup plans

13. Questions / Comments?

14. Tutorial on J2EE Douglas C. Schmidt 14 Java/J2EE to develop Enterprise Applications EE = Enterprise Edition Specifications and Standards Enabled Vendors to build Application Servers Focus on Business Logic, not on infrastructure Removed some complexities, introduced others

15. Tutorial on J2EE Douglas C. Schmidt 15 Standards & Specifications EJB JSP JAXP JMS JNDI JMX Servlets JDBC JTA JCA RMI JNI Some but not all…

16. Tutorial on J2EE Douglas C. Schmidt 16 J2EE Architecture

17. Tutorial on J2EE Douglas C. Schmidt 17 Containers “Containers provide the runtime support for J2EE application components. Containers provide a federated view of the underlying J2EE APIs to the application components. J2EE application components never interact directly with other J2EE application components. They use the protocols and methods of the container for interacting with each other and with platform services. Interposing a container between the application components and the J2EE services allows the container to transparently inject the services defined by the components’ deployment descriptors, such as declarative transaction management, security checks, resource pooling, and state management.” -J2EE Specification v1.4

18. Tutorial on J2EE Douglas C. Schmidt 18 EJB Specification Session, Entity, and Message Driven Beans Instance Lifecycle Declarative Transaction Management Security Threading/Locking Remote/Local Invocation

19. Tutorial on J2EE Douglas C. Schmidt 19 Session Beans Executes on behalf of a single client. Can be transaction-aware. Updates shared data in an underlying database. Does not represent directly shared data in the database, although it may access and update such data. Is relatively short-lived. Is removed when the EJB container crashes. The client has to re- establish a new session object to continue computation. Can be either Stateful or Stateless.

20. Tutorial on J2EE Douglas C. Schmidt 20 When to use Session Beans Session Façade pattern Front end a web service Manage transactions, threading, pooling, etc. Expose a remote interface

21. Tutorial on J2EE Douglas C. Schmidt 21 Entity Beans Provides an object view of data in the database. Allows shared access from multiple users. Can be long-lived (lives as long as the data in the database). The entity, its primary key, and its remote reference survive the crash of the EJB container.

22. Tutorial on J2EE Douglas C. Schmidt 22 When to use Entity Beans Services that have a small limited object model. Object model needs to perform CrUD operations. No complex joins are needed to retrieve data. No need to walk complex object graphs.

23. Tutorial on J2EE Douglas C. Schmidt 23 Message Driven Beans Executes upon receipt of a single client message (JMS). Is asynchronously invoked. Can be transaction-aware. May update shared data in an underlying database. Does not represent directly shared data in the database, although it may access and update such data. Is relatively short-lived. Is stateless. Is removed when the EJB container crashes. The container has to re-establish a new message-driven object to continue computation.

24. Tutorial on J2EE Douglas C. Schmidt 24 When to use MDB Distributed systems JMS Asynchronous calls Manage Transactions, threading, pooling, etc.

25. Tutorial on J2EE Douglas C. Schmidt 25 Bean Lifecycle

26. Tutorial on J2EE Douglas C. Schmidt 26 Declarative Transactions Declare the transaction level through configuration of a bean. Container manages these transactions for you. Valid transaction Values: –Not Supported –Required –Supports –Requires New –Mandatory –Never

27. Tutorial on J2EE Douglas C. Schmidt 27 Application Servers Implement the specification for EJB containers. Provide environment which allows developers to focus on business logic.

28. Tutorial on J2EE Douglas C. Schmidt 28 JBoss Application Server J2EE application server – open source www.jboss.org EJB Container and more Implements Specification through “Interceptors” – AOP-like

29. Tutorial on J2EE Douglas C. Schmidt 29 AOP – Aspect Oriented Programming “Aspect-Oriented Programming (AOP) complements OO programming by allowing the developer to dynamically modify the static OO model to create a system that can grow to meet new requirements. Just as objects in the real world can change their states during their lifecycles, an application can adopt new characteristics as it develops.” -Graham O’Regan

30. Tutorial on J2EE Douglas C. Schmidt 30 JBoss EJB Interceptor Stack

31. Tutorial on J2EE Douglas C. Schmidt 31 Implementing Declarative Transactions using Interceptors Not Supported Required Supports Requires New Mandatory Never

32. Tutorial on J2EE Douglas C. Schmidt 32 Not Supported

33. Tutorial on J2EE Douglas C. Schmidt 33 Required

34. Tutorial on J2EE Douglas C. Schmidt 34 Supports

35. Tutorial on J2EE Douglas C. Schmidt 35 Requires New

36. Tutorial on J2EE Douglas C. Schmidt 36 Mandatory

37. Tutorial on J2EE Douglas C. Schmidt 37 Never

38. Tutorial on J2EE Douglas C. Schmidt 38 Custom Interceptors AOP – Aspect Oriented Programming Logging Timing Metrics Any business logic that should be applied widely

39. Tutorial on J2EE Douglas C. Schmidt 39 Developers Focus on Business Logic