Java Servlets Java 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 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 CGI Servlet JSP Template (ASP, PHP) (in C) (java, C++) Template (ASP, PHP) complexity Speed, Security Servlet JSP

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 servlet Class java.lang.Object Class javax.servlet.GenericServlet javax.servlet.HttpServlet Interface javax.servlet.Servlet javax.servlet.ServletConfig javax.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("<h1>Hello CS764!</h1>"); out.println("</body>"); out.println("</html>"); out.close(); }

<title>Hello CS764!</title></head> <body> <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 Web server (Apache, JWS) Client (browser) Trigger Servlet, JSP (Request) Web server (Apache, JWS) Client (browser) Through internet Return html file (Response) Request data JDBC, intranet Return data Database server (DB2)

Life Cycle of Servlet servlet HttpServlet GenericServlet init(ServletConfig); doGet(HttpServletRequest, HttpServletResponse); service(ServletRequest, ServletResponse); doPost(HttpServletRequest, HttpServletResponse); ……. destroy();

Interaction with Client HttpServletRequest String getParameter(String) Enumeration getParameters(String[]) HttpServletResponse Writer getWriter() ServletOutputStream getOutputStream() Handling GET and POST Requests

Assignment : Get Stock Price Ass2.html <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

Ass2Servlet public class Ass2Servlet extends HttpServlet { 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>"); }

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 Servlets Http: 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

Is a technique that can be used to keep track of users 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 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 servlet 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 Calculator.html <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

Calculator.jsp <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 Declaration Setting property Getting property 1. <jsp:useBean id=“bean1” class=“Bean1”/> 2. <jsp:useBean id=“bean1” class=“Bean1” name=“serBean” type=“SerBean1”/> Setting property 1. <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=“*”/> Getting property 1. <jsp:getProperty name=“bean1” property=“color”/> 2. <%=bean1.getColor() %>

Assg2 example Client side Ass2.html <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><td></td><td><input type="submit" value = "get price"></td></tr> </table> </form></center> </body></html> Client side Ass2.html

<jsp:setProperty name=“ass2” property=“stockSymbol”/> 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> } </table> </center> </h2> <hr><%@include file="ass2.html" %></html> <jsp:setProperty name=“ass2” property=“stockSymbol”/> <jsp:setProperty name=“ass2” property=“stockMarket”/> Server side

Without using JDBC Public 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 --> Database import 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 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