java servlets

05/03/2023University of Education, Okara

1Java ServletsWeb Engineering

Faraz Hashmi, BSIT-5th Eve, 3011


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Servlets are protocol- and platform-independent server side components, written in Java, which dynamically extend Java-enabled servers.

They have become more and more popular as they benefit from all the advantages of the Java programming language in particular Architecture and Platform Independence and the ability to build robust and secure applications.

Servlet


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A Servlet, in simple terms, is a Java program running under a web server taking a 'request' object as an input and responding back by a 'response' object. Typically a web browser will send the request in HTTP format. The Servlet container will convert that into a request object. Similarly the response object - populated by the Servlet is converted into an HTTP response by the Servlet container.

This mechanism makes the browser - web server interaction very easy. Java Servlets are more efficient, easier to use, more powerful, more portable, and cheaper than traditional CGI and many alternative CGI-like technologies.

(More importantly, Servlet developers tend to get paid more than Perl programmers)

Servlet


4 Servlet Mechanism

A servlet is a Java class and thus needs to be executed in a Java Virtual Machine by a service called a servlet engine. The servlet engine loads the servlet before it can be used. The servlet then stays loaded until it is unloaded or the servlet engine is shut down.


5 Servlet Mechanism

Client/Browser Server Servl

et

JVMRequest

Response

Extends the functionality of the server byGenerating HTML pages dynamically


6 Servlet Types

Servlets are based on two main packages javax.servlet javax.servlet.http

GenericServlet For writing protocol independent servlets

HttpServlet Extends from GenericServlet class Adds functionality for writing HTTP specific servlets

Servlet class hierarchy

Object

GenericServlet ServletResponse

HttpServletRequest

ServerRequest

HttpServlet HttpServletResponse

javax.servlet

javax.servlet.http


8 Software Requirements

To use Java servlets, following softwares will be needed

J2SE

Additional J2EE based libraries for servlets such as servlet-api.jar, jsp-api.jar. You can download these APIs separately but they are also available with the web server you’ll be using.

A capable servlet web engine (web server)


9 Environment Setup

Steps

1. Download the Apache Tomcat Server2. Install Tomcat3. Set the JAVA_HOME variable4. Set the CATALINA_HOME variable5. Set the CLASSPATH variable6. Test the Server


10 Servlet Advantages & Disadvantages

The advantage of Servlets is, Portability

o Portable across operating systems and across web servers Power

o Harness the full power of the core Java APIs: networking and URL access, multithreading, image manipulation, data compression, JDBC, object serialization, internationalization Efficiency & Endurance

o Memory resident, so invocation highly efficient—no process to spawn or interpreter to invoke



Safetyo Support safe programming since inherit Java’s strong type

safety, exception-handling mechanism Elegance

o Code is clean, object-oriented, modular, and simple (i.e.. Session tracking, cookie) Integration

o Tightly integrated with the server—translate file paths, perform logging, check authorization, and MIME type mapping



The disadvantage of Servlets is, Web Administrator will need to learn how to install and maintain

Java Servlets Tedious uses of out.println() statements

o Can be remedied by using Java Server Page (JSP)


13 Types of HTTP Requests

Get Post Delete Options Put Trace

How HTTP Sends Request

Client Server

Servlets

Some HTTP request types

• Get -- Attr/Val pairs attached after ? of URL E.g. http://www.gmail.com/register?name=ali

• Post -- Attr/Val pairs attatched with the request body


15 HTTP Request Example

Request parameters etc.


16 Servlet Model


17 Servlet Life Cycle

Initialize Service Destroy


18 HelloWorld Servlet

import java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class HelloWorldServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

PrintWriter out = response.getWriter(); out.println(“Hello World!”);}

}


19 Web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app>

<servlet> <servlet-name>HelloWorldServlet</servlet-name> <servlet-class>HelloWorldServlet</servlet-class> </servlet>

<servlet-mapping> <servlet-name>HelloWorldServlet</servlet-name> <url-pattern>/myfirstservlet</url-pattern> </servlet-mapping>

</web-app>