Applets & Servlets

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Overview This presentation will provide an overview of

the basics of applets and servlets as well as their roles in web development and enrichment. The presentation will answer the following questions:

What is an applet? How do applets work? What is a servlet? How do servlets work? What are the advantages and disadvantages of

servlets? Is there a relationship between applets and servlets?

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What is an applet?

An applet is a Java program that is embedded and ran in some other Java interpreter program such as a Java technology-enabled

browser Sun’s applet viewer program

called appletviewer

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Java Interpreter Programs

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How do applets work? Step 1

Download and install Sun’s Java Software Development Kit (SDK) to allow compilation and interpretation of compiled class files

Write the Java source code for the applet in any text editor.

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How do applets work? Step 2

Compile the source code to obtain the necessary bytecodes known as “.class” for interpreting

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How do applets work? Step 3

Web page

Server

httpserver

applet

image

HTML controls

client

clientWeb page

Web page

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How do applets work? Step 4

httpserver

client

Adventure.class

JVM

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What is a servlet?

A servlet is a Java program that executes on the server side in a special secure environment, such as Inside servlet-support web servers Standalone servlet containers

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What is a servlet? (Cont’d)

Commonly run inside a web server, servlets are dynamically loaded to extend the functionality of the server

Functionally, servlets are an alternative to CGI scripts for creating dynamic web content

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Common Servlet Containers iPlanet (Netscape) Web Server

Enterprise Edition Zeus Web Server World Wide Web Consortium’s Jigsaw

Server Sun’s Java Web Server Apache’s Web Server via JServ

module Apache’s Tomcat Server ***

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How do servlets works? Step 1

Download and install Sun’s Java Software Development Kit (SDK) to allow compilation and interpretation of compiled class files

Download and install servlet-support server

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How do servlets work? Step 2

Write the Java source code for the applet in any text editor.

Compile the source code to obtain the necessary bytecodes known as “.class” for interpreting

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How do servlets work? Step 3

Start the servlet engine to allow servlets to be dispatched

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How do servlets work?

Server

Apache’s WebServer

via JServ

Web page

applet

image

HTML controls

client

client

Port 80JServ Module

System Resources

Scenario 1: Web Server with built-in servlet support

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How do servlets work? Scenario 2: Standalone Servlet Container

Server

Web page

applet

image

HTML controls

client

client

Any PortApache’s Tomcat Server

System Resources

Static Web page

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Servlet Life Cycle

Main Process

JVM

Servlet1

Servlet2

Request for Servlet1

Request for Servlet1

Request for Servlet2

threadthread

thread

Java Servlet-based Web Server

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Servlet Example 1:HelloWorld.java

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Servlet Example 1:Servlet Output

Hello World

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Servlet Example 2:HelloWWW.java

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Servlet Example 2:Servlet Output

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What are the advantages of servlets? Portability

Portable across operating systems and across web servers

Power Harness the full power of the core Java

APIs: networking and URL access, multithreading, image manipulation, data compression, JDBC, object serialization, internationalization

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What are the advantages of servlets? (Cont’d)

Efficiency & Endurance Memory resident, so invocation highly

efficient Safety

Support safe programming since inherit Java’s strong type safety, exception-handling mechanism

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What are the advantages of servlets? (Cont’d)

Elegance Code is clean, object-oriented,

modular, and simple (i.e.. Session tracking, cookie)

Integration Tightly integrated with the server—

translate file paths, perform logging, check authorization, and MIME type mapping

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What are the disadvantages of servlets?

Developers MUST know JAVA Web Administrator will need to

learn how to install and maintain Java Servlets

Tedious uses of out.println() statements Can be remedied by using Java Server

Page (JSP)

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JSP Example: JSP Code

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JSP Example: JSP Output

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Is there a relationship between applets and servlets?

Technically, NO! Thought to be applet that runs on

the server side - without a face Effective in building client/server or

other networked applications

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Browser

Applet/Servlet Model

Server

Web page

applet

image

HTML controls

client

Any PortServlet Engine

System Resources

Applet

Port 80

Any Port

HTML

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Summary Applets bring life to the traditional

HTML pages Servlets create dynamic web pages Both, either working together hand-

to-hand or not, enhance web development by extending server functionality and at the same time, enrich our web experience with interactivity