Lecture3

Server-side Web Programming Lecture 3: Introduction to Java Server Pages

Form Handling Form data appended to request string Generates the request: http://frodo.cis.ysu.edu/~john/cgi-bin/test.pl &quantity=3 <FORM NAME="purchaseform" METHOD=GET ACTION= http://frodo.cis.ysu.edu/~john/cgi-bin/test.pl > Quantity: <INPUT TYPE="text" SIZE="8" NAME="quantity" /> <BR /><BR /> <INPUT TYPE="submit" VALUE="SUBMIT"> </FORM>

Form Handling Goal: Extract values of parameters from the request Generate appropriate response page based on parameter values Take other appropriate action based on request Add to shopping cart Modify or query database

Server Page Model Html document with executable code interspersed When page requested: Code executed Html generated and inserted in its place Final all html document sent back as response request for somepage.jsp Tomcat server somepage.jsp html html Java html Java html html html html Java html html resulting html page html html html html html html html html html html html html

Java Server Pages <HTML> <HEAD><TITLE>cgi-bin response</TITLE></HEAD> <BODY> <P> Thank you for your order of <%= request.getParameter(“quantity”) %> widgets! </P> </BODY> </HTML>

JSP Syntax Basic tag form: <% … %> Simplest form: <%= some Java expression %> Tomcat evaluates expression to get value Inserts that value in place of expression in generated html page

JSP Simple Example Simple example: Java Server Page Resulting html Page 2 + 2 evaluated to value of 4 <html> <body> <p> Two plus two is <%= 2 + 2 %>. </p> </body> </html> <html> <body> <p> Two plus two is 4 . </p> </body> </html>

JSP Syntax Basic tag form: <% … %> Executes code inside brackets without generating html Set variables later used to generate html later Store/access values in session/databases <html> <body> <% int sum = 2 + 2; %> <p> Two plus two is <%= sum %>. </p> </body> </html>

JSP Syntax Stores value of 4 in sum variable Value of 4 in sum used in this JSP No html here <html> <body> <% int sum = 2 + 2; %> <p> Two plus two is <%= sum %>. </p> </body> </html> <html> <body> <p> Two plus two is 4 . </p> </body> </html>

JSP Scoping Variable declared in a block of JSP on a page May be accessed by any other JSP on same page No access to variable from any other page (purpose of sessions ) <html> <body> <% int sum = 2 + 2; %> <p> Two plus two is <%= sum %>. </p> </body> </html>

Html Forms The FORM tag <form action=” url of response page ” method=” get or post ”> … </form> Relative url if response page is part of same webapp Method by which form data is passed

Get vs. Post Method Prevents bookmarking (good if part of session that user should no be able to enter in middle) Allows bookmarking of pages Parameters limited to ~4k of data No fixed limit to length of form data passed Faster Form data not visible (some security against shoulder surfing, but still need encryption for total security) Appends form data to end of URL Must specify in FORM Default method Post method Get method

Simple Form Elements TEXT tag <input type=“text” name=“ elementname ”/> SUBMIT tag <input type=”submit” value=” buttonlabel ”/> Necessary for value to be sent to server

Form Element Example <form action="orderReply.jsp" method="get"> <table cellspacing="5"> <tr> <td align="right">Number to purchase:</td> <td> <input type="text" name="quantity"> </td> </tr><tr> <td align="right">Your name:</td> <td> <input type="text" name="customerName"> </td> </tr><tr> <td align="right">Your email:</td> <td> <input type="text" name="customerEmail"> </td> </tr><tr> <td></td> <td> <input type="submit" value="Place Order"> </td> </tr> </table> <form>

Form Parameter Passing Parameter string passed: quantity=137&customerName=John+Sullins& customerEmail=john@cis.ysu.edu

Handling Form Data request object in JSP Java object created from request string Contains request data and methods to easily access that data Accessed by JSP code Data from form Other data about request methods to access data about the request Code in JSP request

Handling Form Data Most useful method: String request.getParameter( String ) Example: String name = request.getParameter("customerName"); sets the value of “ name ” to “ John Sullins ” Takes name of form element as parameter Returns the corresponding value passed to the server

Example JSP <body> <% String name = request.getParameter("customerName"); String email = request.getParameter("customerEmail"); String quantity = request.getParameter("quantity"); %> <h2>Order Confirmation</h2> <p> Thank you for your order of <%= quantity %> widgets, <%= name %>. </p> <p> You will shortly receive an email confirmation at <%= email %>. </p> </body>

Acquiring Form Data Statements to get and store form data: <% String name = request.getParameter("customerName"); String email = request.getParameter("customerEmail"); String quantity = request.getParameter("quantity"); %> “ 137” quantity “ john@cis.ysu.edu” email “ John Sullins” name

Displaying Values in Response <p> Thank you for your order of <%= quantity %> widgets, <%= name %> . </p><p> You will shortly recieve an email confirmation at <%= email %> . </p> 137 John Sullins [email_address]

Commenting JSP Files Crucial to future maintenance of site Inside of JSP code (between <% and %> ): // comment /* comment */ Outside of JSP code (that is, in html)

Importing Library Classes Much of Java classes in separate libraries Must be imported to be used in JSP Syntax: <%@ page import=” list of Java classes ” %> Example: <%@ page import=”java.util.Date, java.io.*” %> Date class in the util library All classes in the io library

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