java servlets java server pages (jsp). need for servlets servlets are required to: reduce the...
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Java ServletsJava Server Pages
(JSP)
Need for Servlets
Servlets are required to:
Reduce the overhead on the server and network
To take care of processing data on the Web server
Servlets are:
Java programs that can be deployed on a Java enabled Web server
Used to extend the functionality of a Web server
Used to add dynamic content to Web pages
Characteristics of Servlets
Servlets are:
Efficient
Initialization code for a servlet is executed only once
Robust
Provide all powerful features of Java
Portable across Web servers
Persistent
Increase the performance of a system by preventing frequent disk access
Comparison between Servlets and Applets
Applets:
Are embedded in Web pages
Require the browser to be Java-enabled
Take a lot of time to be downloaded
Servlets:
Execute on the Web server, thus help overcome problems with download time
Do not require the browser to be Java-enabled
Comparison between Servlets and other Server-
Side Scripting Technologies
Common Gateway Interface (CGI) scripts, JSP, and ASP are alternatives to servlets
CGI Scripts:
Are programs written in C, C++, or Perl
Get executed in a server
Run in separate processes for each client access
Require the interpreter to be loaded on the server
A JSP file is automatically converted to a servlet before it is executed
Comparison between Servlets and other Server- Side Scripting Technologies (Contd.)
Active Server Pages (ASP):
Is a server-side scripting language developed by Microsoft
Enables a developer to combine HTML and a scripting language in the same Web page
Are not compatible with all Web servers
Overview of History
CGI(in C)
Template(ASP, PHP)
Servlet
CGI(java, C++)
JSP
Speed, Securitycomplexity
Working of Servlets
Client browser passes requests to a servlet using the
following methods:
GET
Uses a query string to send additional information to the server
Query string is displayed in the client browser
POST
Sends the data as packets to the server through a separate socket connection
Complete transaction is invisible to the client
Slower compared to the GET method
The javax.servlet Package• Hierarchy of classes that are used to create a
servletClass java.lang.Object
Class javax.servlet.GenericServlet
Class javax.servlet.HttpServlet
Interface javax.servlet.Servlet
Interface javax.servlet.ServletConfig
Interfacejavax.io.Serializable
The javax.servlet Package (Contd.)• A brief description of the classes and
interfaces are as follows:
Class/Interface Name Description
HTTPServlet class Provides a HTTP specific implementation of the Servlet interface.
HTTPServletRequest interface
Provides methods to process requests from the clients.
Class/Interface Name
Description
HTTPServlet Response interface
Response to the client is sent in the form of a HTML page through an object of the HTTPServletResponse class.
ServletConfig class
Used to store the servlets startup configuration values and the initialization parameters.
Life Cycle of a Servlet• Life cycle of a servlet is depicted below:
Client (Browser)
init()
service()
destroy()
Request
Response
Life Cycle of a Servlet (Contd.)• The following table describes few methods
that are used in creating a servlet:
Method name Functionality
Servlet.init (ServletConfig config) throws ServletException
Contains all initialization code for the servlet.
Servlet. service()
Receives all requests from clients, identifies the type of the request, and dispatches them to the doGet() or doPost() methods for processing.
Life Cycle of a Servlet (Contd.)
Method name Functionality
Servlet. destroy()
Executes only once when the servlet is removed from server.
HTTPServlet Response. getWriter()
Returns a reference to a PrintWriter object.
HTTPServlet Response. setContentType (String type)
Sets the type of content that is to be sent as response to the client browser.
Deploying a Servlet• A servlet can be deployed in:
– Java Web Server (JWS)– JRun– Apache– Java 2 Enterprise Edition (J2EE) server
HelloWorld import java.io.*;import javax.servlet.*;import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<body>"); out.println("<head>"); out.println("<title>Hello CS764!</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>Hello CS764!</h1>"); out.println("</body>"); out.println("</html>");
out.close(); }}
<html><head></head><body><a href="../servlet/HelloWorld"><h1>Execute HelloWorld Servlet</h1></a></body></html>
<html><head><title>Hello CS764!</title></head><body><h1>Hello CS764!</h1></body></html>
Client - Server - DB
Client (browser)
Web server (Apache, JWS)
Database server (DB2)
Through internet
Return html file (Response)
Trigger Servlet, JSP (Request)
JDBC, intranet
Request data
Return data
Life Cycle of Servlet
init(ServletConfig);
service(ServletRequest, ServletResponse);
destroy();
servlet
GenericServlet HttpServlet
doGet(HttpServletRequest,
HttpServletResponse);
doPost(HttpServletRequest,
HttpServletResponse);…….
Interaction with Client
• HttpServletRequest– String getParameter(String)
– Enumeration getParameters(String[])
• HttpServletResponse– Writer getWriter()
– ServletOutputStream getOutputStream()
• Handling GET and POST Requests
Assignment : Get Stock Price
<html><head></head>
<body>
<form action="../servlet/Ass2Servlet" method=POST>
<h2>Stock Symbol name:
<input type=text name="stockSymbol"></h2><br>
<input type="submit" value = "get price">
</form>
</body></html>Client Side
Ass2.html
import java.io.*;import java.util.*;import javax.servlet.*;import javax.servlet.http.*;
public class Ass2Servlet extends HttpServlet { public void doPost(HttpServletRequest request,
HttpServletResponse res) throws IOException, ServletException
{res.setContentType("text/html");
PrintWriter out = res.getWriter();
String stockSymb = request.getParameter("stockSymbol");
StockGrabber sg = new StockGrabber();sg.setStockSymbol(stockSymb); // Set the stock symbol as “input”String stockPrice = sg.getPrice();// Get the price of stock
System.out.println("After StockGrabber.getPrice --"+stockPrice);// Debug out.println("<html><head></head><body><br><br>"); out.println(stockSymb + " -- " + stockPrice);
out.println("<hr>");out.println("<form action=\"../servlet/Ass2Servlet\" method=POST>");
out.println("<h3>Stock Symbol name: <input type=text name=\"stockSymbol\"></h3>");out.println("<input type=submit value=\"get price\">");out.println("</form>");out.println("</body></html>");
}}
Ass2Servlet
Session Tracking
Session:
• Is a group of activities that are performed by a user while accessing a particular Web site
Session Tracking:
• Is the process of keeping track of settings across sessions
Techniques to Keep Track of Sessions in ServletsHttp:•Cannot be used to maintain data across two sessions• Is a stateless protocol
The following techniques can be used to track sessions data in servlets:• URL rewriting • Hidden form fields• Cookies• Using the HTTPSession interface
URL Rewriting • Is a technique by which the URL is
modified to include the session ID of a particular user and is sent back to the client – The session ID is used by the client for
subsequent transactions with the server
Hidden Form Fields• Is a technique that can be used to keep track
of users– The values that are trapped in the hidden fields
are sent to the server when the user submits the form
Using the HttpSession Interface HttpSession Interface:• Is a part of the Servlet API that is used to
keep track of sessions– A user who logs on to a Web site is
automatically associated with a session object– The session object can be used to store any type
of data for keeping track of sessions
Cookies• Are small text files that are used by a Web server to keep track of
users• Has values in the form of key-value pairs• Are created by the server and sent to the client with the HTTP
response headers• Are saved in the client’s local hard disks and sent along with the
HTTP requests headers to the server• Are supported by the Servlet API through javax.servlet.http.Cookie class
Need for JSP
Caters to the need for server-side scripting
Facilitates segregation of work profiles of a Web designer and a Web developer
The Web designer designs the layout for the Web page by using HTML
The Web developer writes the code for business logic by using Java and other JSP-specific tags
Generates a servlet on compilation, hence incorporates all servlet functionalities
Differences between servlets and JSP
Servlets:
Consist of an HTML file for static content and a Java file for dynamic content
Require recompilation if changes are made to any of the files
Involve extensive code writing
JSP:
Contains Java code embedded directly into an HTML page by using special tags
Automatically incorporates changes made to any files
Facilitates independent working of Web developers and Web designers
Java Server Pages (JSP)
Client’s Computer
Server
1.Browser requests HTML
7. Server sends HTML back to browser
servletservlet
class 5.The servlet runs and generates HTML
Java Engine
6. Java Engine sends HTML to server
2. Server sends requests to Java Engine
3. If needed, the Java Engine reads the .jsp file
4. The JSP is turned into a servlet, compiled, and loaded
Bean
The JSP request-response cycle
A First JSP <html>
<head></head>
<body>
<p>Enter two numbers and click the
‘calculate’ button.</p>
<form action=“calculator.jsp” method=“get”>
<input type=text name=value1><br>
<input type=text name=value2 ><br>
<input type=submit name=calculate value=calculate>
</form>
</body>
</html>
Calculator.html
<html><head><title>A simple calculator: results</title></head><body><%-- A simpler example 1+1=2 --%>1+1 = <%= 1+1 %><%-- A simple calculator --%><h2>The sum of your two numbers is:</h2><%= Integer.parseInt(request.getParameter("value1")) + Integer.parseInt(request.getParameter("value2")) %></body></html>
Calculator.jsp
JSP Tags
• Comments <%-- …...text…... --%>
• Declaration <%! int i; %>
<%! int numOfStudents(arg1,..) {} %>
• Expression <%= 1+1 %>
• Scriptlets <% … java code … %>
• include file <%@ include file=“*.jsp” %>
• …...
Using Java Bean
1. <jsp:useBean id=“bean1” class=“Bean1”/>2. <jsp:useBean id=“bean1” class=“Bean1” name=“serBean” type=“SerBean1”/>
Declaration
Getting property1. <jsp:getProperty name=“bean1” property=“color”/>2. <%=bean1.getColor() %>
Setting property1. <jsp:setProperty name=“bean1” property=“color” value=“red”/>2. <jsp:setProperty name=“bean1” property=“color”/>3. <jsp:setProperty name=“bean1” property=“color” param=“bgColor”/>4. <jsp:setProperty name=“bean1” property=“*”/>
Assg2 example
<html><head></head><body><center><table border = 0><form action=ass2.jsp method = POST><tr><td><font color=blue>choose a stock market:</font></td> <td><select name="stockMarket">
<option value="Waterhouse">Waterhouse</option> <option value="Yahoo">Yahoo</option> <option value="ChicagoStockex">Chicago Stockex</option> <option value="Reuters">Reuters</option>
</select></td></tr><tr><td><font color = blue>input a stock symbol:</font></td><td><input type="edit" name="stockSymbol" size=15></td></tr><tr><td></td><td><input type="submit" value = "get price"></td></tr></table></form></center></body></html>
Client sideAss2.html
Server side
ass2.jsp<html><head><jsp:useBean id="ass2" scope="session" class="ass2.StockGrabber" /><jsp:setProperty name="ass2" property="*" /></head> <body><h2><%
ass2.processInput(); ass2.getPrice(); %>
<center><table border=5><tr><td># of data</td> <td>Stock Market</td> <td>Stock Symbol</td> <td>Stock Price </td></tr><%
String[] stockMarkets = ass2.getStockMarkets();String[] symbols = ass2.getSymbols();String[] prices = ass2.getPrices();for(int i=0; i<prices.length; i++){
%><tr><td> <%= i+1 %> </td> <td> <%= stockMarkets[i] %> </td> <td> <%= symbols[i] %> </td> <td><font color=red><%= prices[i] %></font></td></tr><%
} %></table></center></h2><hr><%@include file="ass2.html" %></html>
<jsp:setProperty name=“ass2” property=“stockSymbol”/><jsp:setProperty name=“ass2” property=“stockMarket”/>
Without using JDBCPublic class StockGrabber { ... public void processInput(){ if(stockMarket.compareTo("Waterhouse")==0){ setPrePriceString("<!--Last-->");
setPostPriceString("</FONT>"); setUrlPrefix("http://research.tdwaterhouse.com/
waterhouse/quote.asp?ticker="); } else if(stockMarket.compareTo("Yahoo")==0){ setPrePriceString("<td nowrap><b>"); setPostPriceString("</b></td>"); setUrlPrefix("http://finance.yahoo.com/q?s="); } ... else if(...){} ... else{...} } ...}
Using JDBC --> Databaseimport java.sql.*;Public class StockGrabber { ... public void processInput(){
try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String sourceURL="jdbc:odbc:stockInfo"; Connection databaseConnection=DriverManager.getConnection(sourceURL); Statement statement=databaseConnection.createStatement(); ResultSet info =statement.executeQuery( "select tPrePriceStr, tPostPriceStr, tUrlPrefix
from stockMarketData where tStockMarket = stockMarket”); while(inf.next())
{ prePriceString = info.getString(”tPrePriceStr");
postPriceString = info.getString(“tPostPriceStr”);urlPrefix = info.getString(“tUrlPrefix”);
} }
catch(SQLException e){ ... }...
}}
A JSP page consists of HTML and JSP tags. The JSP tags include comments, directives, declarations, scriplets, expressions, and actions
JSP directives are used to specify general information about a particular page
JSP declarations are used to define variables and methods in a page
JSP scriplets consist of valid code snippets placed within the <% and the %> tags
JSP expressions are used to directly insert values into the output
JSP actions such as useBean, getProperty, setProperty, and forward are used to perform tasks such as insertion of files, reusing beans, forwarding a user to another page, and instantiating objects
JSP implicit objects such as request, response, out, and session are pre-defined variables that can be added to expressions and scriplets You use the java utility to execute a Java program