overview of j2ee

8/9/2019 Overview of J2EE

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Overview to J2EE

By:Jayita Mukhopadhyay


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Why J2EE?

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Presentation world is web-centric

Tried other approaches

Static HTML, CGI, Applets, ASP

Need integration with campus-wide services

Capitalize on developers strengths

Programming

Presentation DBM

Framework is being widely adopted by vendors


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Evolution of J2EE

Advantages of separating view from business logic and datastorage became apparent (MVC Design Pattern)

Enterprise Java Beans (EJB) introduced in 1999 as a way of

isolating server-sided logic into components that were all managedby a container that provided common (and often complicated)runtime management for these components

Sun marketing took Servlets+JSP+EJB+JDBC and packagedthem together as a core enterprise Java Development Kit called

the Java 2 Enterprise Edition, hence the name J2EE

Today also includes Java Messaging (JMS) API, Java DatabaseConnectivity (JDBC), and Remote Method Invocation (RMI)

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J2EE Architecture

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ExternalApplication

Java Technologies

ExternalApplication

Java Technologies


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Web APIs

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Initial Days Applets

Applets

Not part of the J2EE framework

Web-deliverable applications Run on client

Problems

Require correct JVM on client

Difficult to write and change Presentation and logic combined

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Servlets

Servlets

Used for web applications

Extend functionality of an HTTP server

Replace CGIs

Servlet support defined by specification

Filters are part of the spec

Consist of get and post methods for requests

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Anatomy of a Servlet

init() the init() function is called when the servlet is

initialized by the server. This often happens on the first

doGet() or doPut() call of the servlet.

destroy() this function is called when the servlet is

being destroyed by the server, typically when the

server process is being stopped.

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Anatomy of a Servlet

doGet() the doGet() function is called when the servlet is

called via an HTTP GET.

doPost() the doPost() function is called when the servlet

is called via an HTTPPOST.

POSTs are a good way to get input from HTML forms

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Sample Servlet

import java.io.*; //Apache Tomcat

sample code

importjavax.servlet.*;

importjavax.servlet.http.*;

public class HelloWorld extends HttpServlet

{

public void doGet(HttpServletRequest request, HttpServletResponseresponse) throws IOException,

ServletException

{

response.setContentType("text/html");

PrintWriter out = response.getWriter(); out.println("");

out.println(""); out.println("");

out.println("Hello World!");out.println(""); out.println("");

out.println("Hello World!");

out.println(""); out.println("");

}

}

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How do Servlet Engines work?

Server

HTTPD

Servlet Runner

Servlet

HTMLGET/POST

Servlets can be pre-loaded (compiled by

the VM into native code and placed intomemory) makes them as fast as native

code

Servlet invocation creates a new thread

not a new instance of the servlet runner

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Problems with Java Servlets

Any changes to even a simple output required recompiling

the Servlet, uploading it, and restarting the Servlet engine

(disruption in service)

All the View, Data storage/access, and Business logic aretogether in multiple servlets

Difficult to maintain over time

jPortal has >100 servlets and all have database access and

output code intertwined!!

Does not align well with object oriented design/UML

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Problem output from Servlets

HTML output

from a Servlet

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JSP: Dealing with the output

HTML output in Servlets had to be printed into the outgoingstream Hard to maintain any changes to the look&feel required

programmers to change source code, recompile, stop the server,upload the new servlet, start the server again

Solution Java ServerPages Invented byPaul Colton of LiveSoftware, first company to have a

JSP solution for its servlet container

JSP are files that have java source code embedded within tags among HTML they are specialized web pages.

The servlet engine simply converts everything outside these tags

into output print statements on the fly Programmers can edit the HTML in JSPs using an HTML editor

The JSP/servlet engine will covert the HTML lines into output printstatements and recompile into bytecode and reload into memory ---dynamic reloading

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JSP: Introduction

Java ServerPages

Interactive web pages


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Example JSP page

Java code is embedded

within the HTML

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How JSP works

HTTPD

Servlet Runner

Servlets

JSP Converter

jsp page (html+java)

Javaservlet

HTML

1. HTTP-Browser requests

JSP page

2. Parser recognizes JSP

extension means file

should be given to

JSP

/Servlet engine ratherthan sent back to browser

3. JSP container converts

JSP into a java servlet

4. Java servlet is compiled

on the fly and given to the

servlet runner

5. Servlet runner loads

servlet and executes it

6. Output from the servlet is

given to the HTTPD for

return to the browser

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Problems with JSP

Java code in HTML pages difficult to read the javacode and debug

Encourages putting display, data, logic code all

together hard to maintain, not MVC

Looping is difficult/error-prone

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Enterprise JavaBeans (EJB)

EJB Container:Manages security, transactions, and state management, multi-threading, resource pooling, clustering, distributed naming,automatic persistence, remote invocation, transaction boundarymanagement, and distributed transaction management

Deals with common functionality required in business logiccomponents running on a server

Assumes a genericclient-server framework, of which the Web isone of many

Basically, a java server plug-in architecture where rather thanbuilding/re-building a server connection/security / clusteringcomponent, you simply create the functional modules and plug theminto such a framework already built (EJB container)

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EJB

Enterprise Java Bean

Bean

originally a Java class with get() and set() methods e.g.:getFirstName(), setFirstName()

EJBs come in 3 flavors:

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EJB Entity Bean

Entity Bean

Represent actual data items (e.g. rows in a result set)

Two forms of Entity Bean

Container managed persistence: DB interactions handled by the

J2EE environment

Bean managed persistence:requires that the bean carries out DBinteractions itself

May be called across network connection (RMI)

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Session Bean

Model a process or task

Represent resources private to the client

May update shared data

Two forms of Session Bean

Stateful: state maintained between method calls

Stateless

One client per session bean instance

EJB Session Bean

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When to use EJB?

EJBs are not required components of a web

application web apps must be servlets, but

can be JSP, and sometimes can invoke EJBs

EJBs are an advantage when: one has business logic that is easily

compartmentalized

one needs/wants a high degree of scalability (for

example, distribute processing among multi-machine cluster)

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JDBC

Java DataBase Connectivity

Java equivalent of ODBC (Open DataBase Connectivity)

Java API that enables Java programs to execute SQL

statements. This allows Java programs to interact with

any SQL-compliant database

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JTA

Java Transaction API

Specifies standard interfaces between a transaction manager

(e.g. JBoss) and the parties involved in a distributed transaction

system:

the resource manager

the application server

and the transactional applications

Two types of transaction paradigm Declarative for entity & session beans

Programmaticfor session beans & servlets

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JMS

Java Message Service

Point to point messaging

each message has only one

consumer

used to decouple applications

Publish/subscribe messaging

each

message mayh

ave

multiple consumers

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JNDI

Java Naming & Directory Interface

Provides namespace support for J2EE

Beans located by name within container namespace

Application attributes located by name within application local

namespace

Controlled access from external servers

Access to LDAP directories

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JAAS

Java Authentication and Authorization Service

Implements a Java version of the standard Pluggable

Authentication Module (PAM) framework

Supports user-based authorization

Access control at every level

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Java tools forWeb Applications

Java Servlets

Java ServerPages (JSP)

Java Tag Libraries

Jakarta Struts JDBC, JMS

Enterprise Java Beans (EJB)

JavaMail (all e-mail capabilities)

JNDI (java naming and directory services)

Emerging additional frameworks Hibernate (object-relational persistence bridge)

AspectJ (cross cutting code insertion)

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J2EE Applications

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Anatomy of J2EE Web Application

MVC designed Apps typically

include:

View (JSPs)

Controller (one ActionServlet)

Model (EJB or javabeans as

needed)

Object-relational

bridge/connection pooling (forapps that use databases)

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THANK YOU

overview of j2ee

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