This document summarizes key points from a Java & JEE training session on servlets. It discusses SQL injection exercises and form validation. It demonstrates validating forms using JavaScript on the client-side and Java on the server-side. Examples are given for JavaScript form validation, including checking for non-empty fields and restricting input length. The document also covers redirecting requests to other resources using response.sendRedirect() and includes code examples of redirecting. Finally, it previews topics for the next session, which will cover validation, redirection, and request scope in web applications.

1. Java & JEE Training
Session 28 – Servlets - Part 4

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Agenda…
• SQL Injection continued… + Exercises
• Validating forms
• Redirecting requests to other sources

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Review of previous session…
….

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Web Server and Application Server
Presentation Tier:
JSP, Servlets
Run on Web Server
or container
JDBC on web server
or app server
Database
Client:
HTML JS CSS
(Run on client
machine on the
browser)

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Demo of complete Web app flow…
• Form which takes two fields… Student ID and Student Name…
• Output should show whether that row exists or not, and if it exists, how
many records in the table match the criteria (id, name)
• If match found, then print login successful, else login failed.

6. Validation in web apps

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Validating forms using JavaScript..
Best practice
• MUST always validate both on client side as well as server side.
• Validation in the client side is done using JavaScript.
• Validation in the server side is done using Java.
• Demo of frontend and backend validation.
• Example of JS validation.
• Check if value entered is a number or not:
if (data === parseInt(data, 10))
alert("data is integer")
else
alert("data is not an integer");

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More JS Validation Examples….
• Let us look at some validation examples…

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Check for non-empty field…
// If the length of the element's string is 0 then display helper message
function required(inputtx) {
if (inputtx.value.length == 0) {
alert("message");
return false;
}
return true;
}

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Check for restricting length of input field…
function lengthRange(inputtxt, minlength, maxlength)
{
var userInput = inputtxt.value;
if(userInput.length >= minlength && userInput.length <= maxlength){
return true;
}
else{
alert("Please input between " +minlength+ " and " +maxlength+ "
characters");
return false;
}
}

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Reference for more validation examples…
• A good reference for form validation..
http://www.w3resource.com/javascript/form/javascript-form-validation.php

12. Redirecting requests to other sources

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12
Redirecting Requests to Other Resources
• Servlet RedirectServlet
• Redirects the request to a different resource
• Why not just have links to those resources?
• Could determine browser type and choose link accordingly
• Could add parameters before redirecting (those sent originally are
included automatically)
• response.sendRedirect(URL);
• redirects to that URL
• immediately terminates current program
• Use relative paths whenever possible to make Website portable

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RedirectServlet redirecting requests to other resources.
1 // RedirectServlet.java
2 // Redirecting a user to a different Web page.
3
4 import javax.servlet.*;
5 import javax.servlet.http.*;
6 import java.io.*;
7
8 public class RedirectServlet extends HttpServlet {
9
10 // process "get" request from client
11 protected void doGet( HttpServletRequest request,
12 HttpServletResponse response )
13 throws ServletException, IOException
14 {
15 String location = request.getParameter( "page" );
16
17 if ( location != null )
18
19 if ( location.equals( "deitel" ) )
20 response.sendRedirect( "http://www.deitel.com" );
21 else
22 if ( location.equals( "welcome1" ) )
23 response.sendRedirect( "welcome1" );
24
13
Obtains the page parameter from the
request.
Redirects the request to
www.deitel.com.
Redirects the request to the servlet
WelcomeServlet.

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CRUD…
• Select
• Update
• Insert
• Delete
• 1. /Hello?op=Insert OR /Hello?op=Delete
• 2. /Hello/Insert OR /Hello/Delete

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RequestDispatcher forward()
RequestDispatcher rd=request.getRequestDispatcher(“<another servlet>");
rd.forward(request, response);

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RequestDispatcher include()
out.print(“<Your message to include goes here>");
RequestDispatcher rd=request.getRequestDispatcher(“nameOfHTMLorJSP");
rd.include(request, response);

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Request Dispatcher Demo

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Topics to be covered in next session
• Validation of Web Applications
• Redirecting requests
• Understanding Scope: parameters, attributes

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Thank you!