Overview of The Java Platform Solution for E-Business Applications : JSP, Servlet and EJB
Overview of The Java Platform Solution for E-Business Applications : JSP, Servlet and EJB.
Dec 20, 2015
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Overview of The Java Platform Solution for E-Business Applications :
JSP, Servlet and EJB
Outline
Big pictureServlets JavaServer PagesEJB
Multi-Tiered Web-based application
Browser
HTML
Browser
XML
Web Server
Servlet
JSP
EJB Server
EJB
EJB
DB
DB
What are Servlets?
Extend HTTP Server Dynamic content
Servlets are lightweight Run in web server process exploit Java security
Built on Java Platform Full access to Java APIs Easy to develop. Write once, run anywhere
HTTP Requests & Response
Client makes HTTP request Request is resolved to Servlet Container
creates servlet invokes init() creates request and response objects invokes service()
Sevlet interact with response Container replies to HTTP request Container may
invoke destroy(), dispose servlet at anytime
A servlet example
public class HelloServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response) {
response.setContentType("text/plain");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("Hello World!");
out.println("<br>");
JspCalendar clock = new JspCalender();
out.println("Today is");
out.println("<ul>");
out.println("<li>Day of month: ");
out.println(clock.getDayofMonth());
out.println("<li>Year: ");
out.println(clock.getYear());
out.println("/<ul>");
out.println("</html>");
}
}
As a JSP page
<html>
Hello World!
<br>
<jsp:useBean id="clock"
class="calendar.JspCalendar">
Today is
<ul>
<li>Day of month:<%=clock.getDayofMonth()%>
<li>Year: <%=clock.getYear()%>
</ul>
</html>
JavaServer Pages (JSP)
JSP builds on servlet semantics “inside-out” servlets (JSP can be precompiled into Servlet to reduce
start up time)
Benefits Easier to author, separate presentation logic from business logic
Exploits: server-side scripting templates encapsulation of functionality
Distributed Java Component Model -
The Problem
• Developing enterprise applications is HARD• Developing enterprise applications is EXPENSIVE• Enterprise applications are a NIGHTMARE TO MAINTAIN• Enterprise applications are COMPLEX TO ADMINISTER
Why is it HARD?
Difficult to reuse application code across hardware platforms software platforms servers databases
Service needs grow more complex threading persistence transactions
What is EJB?
It’s server component model It’s part of Java platform for the enterprise It’s a specification (for software interoperability) It enables development and deployment of Java
applications that are:
• Distributed – via RMI• Scalable • Transactional • Secure
Distributed component models -we are in heaven ...
CORBAServerService
RMIServerService
IIOPIIOPIIOP
RMIClient
JRMP
The underlying mechanism...
Advantages of server side component model
Using pre-developed pieces of application Transparent access to the distributed
services, i.e. hiding the complexity of the technical environment
Components can be shared across the Enterprise
Using tools to wire components together
EJB Architecture
EJB Architecture
EJB Main Components
Client Any application or service requesting a service Can be written in any language Can’t access EJBs directly; must go through RMI and container Name lookup via JNDI
EJB Servers Contains and runs 1 or more containers Resource management
process, thread, and connection pools Remote management API
EJB Main Components
EJB Containers Actually host the beans Provide naming (via JNDI), life cycle, persistence,
security, transactions through call interception EJB Components
Are distributed, transactional, and secure Simple, single threaded, and non-re-entrant Developer or tool generated Contain business logic
Roles in developing EJB
Enterprise Bean provider Application Assembler Deployer EJB Server Provider System Administrator
Varieties of EJBs
Session beans Model application tasks Not shared, client specific Transient state Short lived
Example – an object holds the logic for purchasing product items i.e. buyProduct
Varieties of EJBs
Entity bean Model persistent resources Shared by clients Persistent state Long lived
Example – a product to be purchased in a shop
Programming basics – Classes and Interfaces
Remote interface Defines the bean’s business methods Extends javax.ejb.EJBObject
Home interface Defines the bean’s life cycle methods (creating,
removing and finding a bean) Extends javax.ejb.EJBHome
Programming basics – Classes and Interfaces
Bean class Must have methods matching the signatures of
the methods defined in the remote interface Must have methods corresponding to some of the
methods in the home interface Primary key
Provides a pointer into the database Only entity beans need a primary key
The Unseen Pieces
Client EJB Server
home interface
EJB homehome interface
EJB home stub
EJB Object
remote interface bean class
remote interface
EJB object stub
RMI allows the downloadable stub
Big picture again
Several good introduction material on the web
http://java.sun.com/products/ejb/articles/multitier.html
This article shows a very good example on how to use EJB to develop multi-tier application!!! The example pretty much covers every thing (Session Bean, EntityBean and Servlet).
http://java.sun.com/products/ejb/faq.html
The FAQs on Sun EJB web site answered many general questions regarding to EJB.
http://internt.isk.kth.se/~enander/DistObj/ejb/ejbpre.htm
here's a good EJB presentation
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