Servlet FudamentalsServlet Fudamentals

E-CommerceUnit-2

Three tier ModelThree tier ModelBy means of a three tier model, we can separate the

business logic of the web application from “frontend”(web client) to the “backend” (database).

The First tier- Web Client◦ Provides a web based GUI displayed through a web browser in

the client computer.◦ Implementation of the web client in the web application is called

“Web Publishing” and “Client Side Programming”

The Second tier- Server Side application◦ Consists of server side applications that run on a web server or a

dedicated application server.◦ Server side programming techniques are-

Common Gateway Interface (CGI) Active Server Pages(ASP) Java Servlets

The third tier- DBMS◦ Provides data storage/retrieval services for the second tier so that

dynamic web pages can be created.◦ To bridge the second tier SSA’s and the backend DBMS, there are

many ways for database connectivity.◦ Most popular method is by means of JDBC such as JDBC-ODBC(Java

database Connectivity-Open Database Connectivity) bridge.

CGI – Common Gateway InterfaceCGI – Common Gateway Interface

Need for CGINeed for CGI

HTML/XHTML is static, it is not parameterized;

using only HTML/XHTML, CSS and JS one can not write dynamic web pages: pages that look differently depending on the user who visit it (client, administrator etc.), pages that display different products depending on what is in a database, pages that should be displayed depending on the value of some parameters.

using only HTML/XHTML, CSS and JS one can not develop distributed web applications (e-commerce sites, hotel booking, web search applications etc.)

OverviewOverview

A plain HTML document is staticA CGI program is executed in real-time, so that

it can output dynamic information.CGI (Common Gateway Interface) is the language

or protocol that the browser uses to communicate the data from the form to the web server.

A standard for interfacing external applications with information servers, such as HTTP or Web servers.

When the user submits his/her answers on a form, the browser bundles them up and sends them to the web server, which passes them on to your CGI script/program for processing. ◦ The web page itself does not process the data

entered on the form. Neither does the web server.

A CGI script/program is any program which knows how to read that bundle of data.◦ The script/program must build up and return the

html source for a web page◦ Shell and Perl scripts are easier and are more

commonly used for CGI scripts.

What is CGI?What is CGI?a standard protocol for interfacing external application

software with the web serverdeveloped in 1993 at NCSA (National Center for

Supercomputing Applications)CGI 1.1 specified in RFC 3875, 2004allows an external executable file to respond to an HTTP

Request from the browserCGI defines how information is passed from the web server

to the executable program and how information is passed from this back to the server

Server-side web programmingServer-side web programming

the HTTP Response consists of the output of an exernal program located on the server machine:

browserweb server

HTTP Request

HTTP Response

executable file/CGI,php file, jsp file, aspfile

Server-side Request

Response Header +Html file

2 methods-◦ Visit Counter

< IMG SRC=“/cgi-bin/visit-counter”>

This causes the web browser to start a CGI script on the server side on encountering the <IMG> tag.

◦ HTML Form To pass Data from web client to the web Server for data

processing using HTML forms, one can include the CGI program called “order.pl” in the <FORM> tag.

<FORM METHOD=“POST” ACTION=“/cgi-bin/order.pl”>

The Action attribute invokes the CGI script.

It is a Perl Script called “orde.pl” stored under the “cgi-bin” directory of the web server.

Drawbacks of CGIDrawbacks of CGI

because no special web-oriented language is used for writing CGI scripts (e.g. shell, perl, c/c++, python etc.) errors are highly probable and so, security vulnerabilities due to these problems

usually a new process is created for each run of a CGI script; this increases the load on the server

CGI scripts are executable file; they can write/delete from the local disk, so this is a security vulnerability

Active Server Pages (ASP)Active Server Pages (ASP)To develop Interactive web pages, Microsoft introduced

a server side programming tool called ASP.ASP is a “scripting” technique that runs on web servers

rather than web clients, unlike JavaScript and VBScript.

It generates dynamic HTML documents for the web client.

Execution of the ASP Code by the server returns the corresponding HTML document to the client.

The server-side code written in ASP can be embedded in the HTML document, which allows one to insert it into web pages even though it is executed on server.

Disadvantages of ASPDisadvantages of ASP

Not a formal programming language, so debugging can be more difficult.

Not object-oriented

24.1 Introduction24.1 Introduction◦ Servlets – Web-based solutions

Secure access to Website Interact with databases Dynamically generate custom HTML documents

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Overview of Java ServletOverview of Java Servlet

ServletsServlets

What can you build with Servlets?What can you build with Servlets?

Search EnginesE-Commerce ApplicationsShopping CartsProduct CatalogsIntranet ApplicationsGroupware Applications: ◦ bulletin boards ◦ file sharing

Servlets vs. CGIServlets vs. CGI

A Servlet does not run in a separate process.

A Servlet stays in memory between requests.

A CGI program needs to be loaded and started for each CGI request.

There is only a single instance of a servlet which answers all requests concurrently.

Browser 1

WebServer

Browser 2

Browser N

Perl 1

Perl 2

Perl N

Browser 1

WebServer

Browser 2

Browser N

Servlet

Performance ◦ The performance of servlets is superior to CGI because there is no

process creation for each client request. ◦ Each request is handled by the servlet container process. ◦ After a servlet has completed processing a request, it stays resident in

memory, waiting for another request.Portability◦ Like other Java technologies, servlet applications are portable.

Rapid development cycle◦ As a Java technology, servlets have access to the rich Java library that

will help speed up the development process.Robustness◦ Servlets are managed by the Java Virtual Machine. ◦ Don't need to worry about memory leak or garbage collection, which

helps you write robust applications.Widespread acceptance◦ Java is a widely accepted technology.

Benefits of Java Servlets

DefinitionsDefinitions

A servlet is a Java class that can be loaded dynamically into and run by a special web server.

This servlet-aware web server, is known as servlet container.

Servlets interact with clients via a request-response model based on HTTP.

Therefore, a servlet container must support HTTP as the protocol for client requests and server responses.

A servlet container also can support similar protocols such as HTTPS (HTTP over SSL) for secure transactions.

Servlet Overview and ArchitectureServlet Overview and Architecture

Servlets used when small portion of content sent to client is static

Java Server Pages (JSPs) used when only small portion of content set to client is dynamic, most is static

HyperText Transfer Protocol (HTTP)Uniform Resource Locator (URL)Servlets communicate between clients

and servers using HTTP27

Servlet Overview and ArchitectureServlet Overview and Architecture

Client sends HTTP requestServlet container receives request,

directs it to the appropriate servletServlet does processing (including

interacting with databases)Servlet returns results to client in form

of HTML document

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Browser HTTP Server

Static Content

ServletContainer

HTTP Request

HTTP ResponseServlet

Servlet Container ArchitectureServlet Container Architecture

Servlet APIsServlet APIs

Every servlet must implement javax.servlet.Servlet interface

Most servlets implement the interface by extending one of these classes◦ javax.servlet.GenericServlet◦ javax.servlet.http.HttpServlet

Initializationinit()

Serviceservice()

doGet()doPost()

doDelete()doHead()doTrace()

doOptions()

Destructiondestroy()

Concurrent Threadsof Execution

Servlet Life CycleServlet Life Cycle

Servlet ExampleServlet Example

1: import java.io.*; 2: import javax.servlet.*; 3: import javax.servlet.http.*; 4: 5: public class MyServlet extends HttpServlet 6: { 7: protected void doGet(HttpServletRequest req, 8: HttpServletResponse res) 9: {10: res.setContentType("text/html");11: PrintWriter out = res.getWriter();12: out.println( "<HTML><HEAD><TITLE> Hello You!” +13: “</Title></HEAD>” +14: “<Body> HelloYou!!!</BODY></HTML>“ );14: out.close();16: }17: }

An Example of Servlet (I)An Example of Servlet (I)

Lines 1 to 3 import some packages which contain many classes which are used by the Servlet (almost every Servlet needs classes from these packages).

The Servlet class is declared in line 5. Our Servlet extends javax.servlet.http.HttpServlet,

the standard base class for HTTP Servlets.

In lines 7 through 16 HttpServlet's doGet method is getting overridden

An Example of Servlet (II)An Example of Servlet (II)

In line 12 we request a PrintWriter object to

write text to the response message.

In line 11 we use a method of the HttpServletResponse object to set the content type of the response that we are going to send. All response headers must be set before a PrintWriter or ServletOutputStream is requested to write body data to the

response.

In lines 13 and 14 we use the PrintWriter to write the text of type text/html (as specified through the content type).

An Example of Servlet (III)An Example of Servlet (III)

The PrintWriter gets closed in line 15 when we are finished writing to it.

In lines 18 through 21 we override the getServletInfo() method which is supposed to return information about the Servlet, e.g. the Servlet name, version, author and copyright notice. This is not required for the function of the HelloClientServlet but can provide valuable information to the user of a Servlet who sees the returned text in the administration tool of the Web Server.

Server Side Programming: Database Server Side Programming: Database ConnectivityConnectivity

IntroductionIntroduction As most databases are relational, the SQL plays an important role

in web-based database interactions in these e-commerce applications.

All types of e-com apps, ranging from B2C applications such as e-shopping to B2B applications such as virtual marketplace, require one to connect to and access information from the back end database system.

An Application Program Interface(API) is a

useful piece of middleware, which provides an interface that allows one to access the necessary functionality for that application.

Java provides an API, JDBC, to allow one to develop web applications that can access and update backend database systems.

Am imp feature of JDBC is that it is database independent.

JDBCJDBCIs an API spec. whose implementation

comes in the form of jdbc drivers.JDBC API :◦ java.sql.*◦ javax.sql.*

JDBC DriverJDBC DriverIs a bridge s/w between java application

and database s/w.Is a java class that implements

java.sql.Driver interface.Why we use JDBC Driver?

JDBC ArchitectureJDBC Architecture

Java code calls JDBC libraryJDBC loads a driver Driver talks to a particular databaseCan have more than one driver -> more than one

database

Application JDBC Driver

JDBC DriversJDBC DriversType I: “Bridge”Type II: “Native”Type III: “Middleware”Type IV: “Pure”

Type 1 Driver (Type 1 Driver (jdbc - odbc bridge driver )jdbc - odbc bridge driver )

Java App that uses JDBC API

Jdbc driver type1

ODBC Driver for Oracle

ODBC Driver for MS-Access

Oracle DB

MS Access

Vendor DB Library for Oracle

Vendor DB Library for M S Access

JDBC Drivers (Fig.)JDBC Drivers (Fig.)

JDBC

Type I“Bridge”

Type II“Native”

Type III“Middleware”

Type IV“Pure”

ODBCODBCDriver

CLI (.lib)

MiddlewareServer

Steps to develop java/jdbc AppSteps to develop java/jdbc Appjava.sql

Classes------------

TypesDriverManagerDateTimeStamp

Interfaces ---------------ConnectionStatementResultSet

DriverPreparedStatementCallableStatement

Steps to develop java/jdbc AppSteps to develop java/jdbc AppLoad the JDBC Driver class and register

with DriverManager.Establish the connection with database

s/w.Prepare Statement objectExecute the query.Get result and process the resultClose the connection.

Preparing for Your First JDBC Preparing for Your First JDBC programprogram

To start with:-