This set of slides introduces the basic concepts of Java development. First, the difference between Java as the programming language and Java as a platform is stated. Then, the different Java platforms are presented, with a particular interest in Java Standard Edition and Java Enterprise Edition. With respect to the latter, the roles and differences between the many JEE containers are discussed.

1. Java & Java pla(orms
Ilio Catallo - info@iliocatallo.it

2. Outline
• Java technology
• JEE applica2ons
• References

3. Java technology

4. Java technology
Java is both a programming language and a pla-orm

5. The Java programming language
The Java programming language is a high-level, object-oriented
programming language firstly released in 1995
class App {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}

6. Pla$orms
A pla$orm is the hardware and so.ware environment in which a
program runs

7. Java pla'orms
A Java pla'orm is a par(cular environment in which Java
applica(ons run

8. Pla$orms
Pla$orms usually consist of a combina2on of the opera&ng system
and the underlying hardware

9. Pla$orms
Example: Microso) Windows on Intel architecture

10. Java pla'orm
The Java pla*orm is a so#ware-only pla*orm that runs on top of
other pla*orms
┌───────────────────────────────────┐
│ Java program │
├───────────────────────────────────┤
│ Java platform │
├───────────────────────────────────┤
│ Host platform │
└───────────────────────────────────┘

11. Java pla'orm
Every Java pla+orm consists of:
• A Java Virtual Machine (JVM)
• A set of applica8on programming interfaces (APIs)

12. Java virtual machine
The Java Virtual Machine (JVM) is an abstract computer that runs
compiled Java programs
┌───────────────────────────────────┐
│ Java program │
├─────────┬─────────────────────────┤
│ API │ │
├─────────┘ Java VM │
│ │
├───────────────────────────────────┤
│ Host platform │
└───────────────────────────────────┘

13. Java virtual machine
The JVM is virtual because it is implemented in so7ware on top of
a real host pla:orm
┌───────────────────────────────────┐
│ Java program │
├─────────┬─────────────────────────┤
│ API │ │
├─────────┘ Java VM │
│ │
├───────────────────────────────────┤
│ Host platform │
└───────────────────────────────────┘

14. Java virtual machine
Java programs are compiled into Java bytecode

15. Java virtual machine
Java bytecode is the machine language of the JVM

16. Java API
The Java API is a large collec2on of ready-made so9ware
components

17. Java API
It is grouped into libraries (packages) of related classes and
interfaces

18. Java API
For instance, the Collec0on API (java.util) provides the most
commonly used data structures

19. Java pla'orm specifica0ons
There exist three Java pla/orm specifica4ons
• Java Standard Edi-on
• Java Enterprise Edi-on
• Java Micro Edi-on

20. Java pla'orm specifica0ons
There exist three Java pla/orm specifica4ons
• Java Standard Edi,on
• Java Enterprise Edi,on
• Java Micro Edi-on

21. Java Standard Edi,on
Java Standard Edi,on (JSE) is a pla,orm specifica3on for
developing desktop applica,ons

22. Java Standard Edi,on
Java Standard Edi,on is the founda,on for developing in the Java
language, as it contains the set of Java standard libraries

23. Java Standard Edi,on
Java Standard Edi,on is just a specifica(on, not an implementa,on

24. Java Standard Edi,on
Vendors and open source projects are free to provide their own
implementa6on
• Oracle JDK
• OpenJDK

25. Java Enterprise Edi.on
Java Enterprise Edi.on (JEE) provides APIs and the run6me
environment for developing enterprise applica.ons

26. Java Enterprise Edi.on
Typical features of an enterprise applica1on
• Large-scale
• Distributed
• Highly-available

27. Java Enterprise Edi.on
Java Enterprise Edi.on is a superset of Java Standard Edi.on

28. Java Enterprise Edi.on
Therefore, JSE APIs can be used in any JEE applica:on

29. Java Enterprise Edi.on
JEE extends the JSE pla/orm with addi$onal APIs:
• Java Servlet API (javax.servlet)
• JavaServer Pages API (javax.servlet)
• Java Persistence API (java.persistence)
• Enterprise JavaBeans API (javax.ejb)

30. JEE specifica+on
Java Enterprise Edi.on is just a specifica(on, not an
implementa.on

31. JEE specifica+on
Namely, JEE is an umbrella specifica.on that references a number
of other more detailed specifica9on
┌──────────────────────────────────────────────┐
│ ┌──────────────┐ │
│ │ EJB │ │
│ ┌─────────────┐ │Specification │ │
│ │ Servlet │ └──────────────┘ │
│ │Specification│ │
│ └─────────────┘ ┌─────────────┐ │
│ │ JPA │ │
│ ┌─────────────┐ │Specification│ │
│ │ JSP │ └─────────────┘ │
│ │Specification│ │
│ └─────────────┘ │
└──────────────────────────────────────────────┘
JEE specification

32. JEE implementa,ons
Vendors and open source projects are free to implement one or
more JEE APIs
┌──────────────────────────────────────────────┐
│ ┌──────────────┐ │
│ │ EJB │ │
│ ┌─────────────┐ │Specification │ │
│ │ Servlet │ └──────────────┘ │
│ │Specification│ │
│ └─────────────┘ ┌─────────────┐ │
│ │ JPA │ │
│ ┌─────────────┐ │Specification│ │
│ │ JSP │ └─────────────┘ │
│ │Specification│ │
│ └─────────────┘ │
└──────────────────────────────────────────────┘
JEE specification

33. JEE implementa,ons
"Apache Tomcat 8.0 implements the Servlet 3.1 and JavaServer Pages
2.3 specifica?ons"
(Apache Tomcat 8.0 documenta3on)

34. JEE implementa,ons
"In addi(on to its own "na(ve" API, Hibernate is also an
implementa(on of the Java Persistence API (JPA) specifica(on"
(Hibernate ORM)

35. JEE Applica*ons

36. JEE Components
Java EE applica*ons are made up of components

37. JEE Components
A JEE component is a self-contained so/ware unit

38. JEE Components
You may already know a par0cular JEE component: servlets
public class MyServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response);
public void doPost(HttpServletRequest request,
HttpServletResponse response);
public void init();
public void destroy();
}

39. JEE Components
There exist different types of JEE components
• Web components
• Business components
• Applica3on client components

40. JEE Components
Web components:
• Servlets
• JavaServer Pages (JSP) and JavaServer Faces (JSF)

41. JEE Components
Business components:
• Enterprise JavaBeans

42. JEE Components
Applica'on client components:
• Applets
• Applica+on Clients

43. JEE Containers
JEE components live within a container. A container is the JEE
run6me environment

44. JEE Containers
A container provides certain services to the components it hosts,
such as:
• Life-cycle management
• Dependency injec4on
• Concurrency

45. JEE Containers
Different kinds of components live in different kinds of containers

46. JEE servers
A Java EE server (also called applica&on server) implements the
en6re set of JEE APIs and provides the standard JEE containers

47. JEE servers
The reference JEE server is Oracle Glassfish. Possible alterna8ve
implementa8ons:
• IBM WebSphere
• Apache TomEE
• Red Hat JBoss

48. JEE servers
JEE server
┌────────────────────────────────────────────────────┐
│ Web container EJB container │
│ ┌──────────────────────┐ ┌─────────────────────┐ │
│ │ ┌─────────────┐ │ │ ┌─────────────┐ │ │
│ │ │ Servlet A │ │ │ │ EJB D │ │ │
│ │ └─────────────┘ │ │ └─────────────┘ │ │ ┌──────┐
┌─────────┐ │ │ ┌──────────┐│ │ ┌──────────┐│ │ │ │
│ Browser ├───┼─┤ │ JSP C │├───┤ │ EJB E │├─┼───┤ DB │
└─────────┘ │ │ └──────────┘│ │ └──────────┘│ │ │ │
│ │┌─────────────┐ │ │┌─────────────┐ │ │ └──────┘
│ ││ Servlet B │ │ ││ EJB F │ │ │
│ │└─────────────┘ │ │└─────────────┘ │ │
│ └──────────────────────┘ └─────────────────────┘ │
└────────────────────────────────────────────────────┘

49. Business logic
At the heart of any applica0on lies its business logic

50. "We call business logic any program code that pertains to the purpose
of a so6ware applica8on"

51. Business logic
In a chess game, the business logic handles:
• The board and pieces
• Their movements
• The rules of the game

52. Business logic
Such concerns are independent of, e.g., how pieces will be
displayed

53. Business logic
Such concerns are independent of, e.g., how pieces will be
displayed

54. The role of EJBs
In a JEE applica+on, EJBs encapsulate the business logic
@Stateless
public class FlightServiceBean {
List<SpecialDeal> getSpecialDeals() { ... }
List<Flight> findFlights(String queryString) { ... }
}

55. The role of EJBs
Moreover, the EJB container provides fundamental services such as
security and transac+ons
@Stateless
@TransactionManagement(TransactionManagementType.CONTAINER)
public class FlightServiceBean {
List<SpecialDeal> getSpecialDeals() { ... }
List<Flight> findFlights(String queryString) { ... }
}

56. The role of EJBs
Thanks to this, developers are free to focus of defining and
implemen6ng the business logic

57. JEE stack
However, many vendors and open source projects implement only
a subset of the JEE specifica;on

58. JEE stack
For instance, Apache Tomcat provides only a Web container

59. Web container
Web server
┌──────────────────────────┐
│ │
│ Web container │
│ ┌──────────────────────┐ │
│ │ ┌─────────────┐ │ │
│ │ │ Servlet A │ │ │
│ │ └─────────────┘ │ │ ┌──────┐
┌─────────┐ │ │ ┌──────────┐│ │ │ │
│ Browser ├───┼─┤ │ JSP C │├─┼───┤ DB │
└─────────┘ │ │ └──────────┘│ │ │ │
│ │┌─────────────┐ │ │ └──────┘
│ ││ Servlet B │ │ │
│ │└─────────────┘ │ │
│ └──────────────────────┘ │
│ │
└──────────────────────────┘

60. Can we built enterprise applica0ons without the whole JEE stack?

61. Can we write enterprise applica.on without the need of an applica.on
server?

62. The Spring Framework
The solu)on comes in the form of the Spring framework

63. The Spring Framework
…but this is something we will inves1gate in the next lecture ;-)

64. References

65. References
• Antonio Goncalves, Beginning Java EE 7, Apress Publica:ons
• Chris Richardson, POJOs in Ac:on, Manning Publica:ons
• D, Panda, R. Rahman, D. Lane, EJB3 In Ac:on, Manning
Publica:ons
• Oracle, GeGng Started

66. References
• Bill Venners, The lean, mean, virtual machine
• Oracle, Java EE 7 Tutorial
• Wikipedia, Java EE