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Servlets

Servlets. Servlets. - Java technology for Common Gateway Interface (CGI) programming. - It is a Java class that dynamically extends the function of a web server. WEB SERVER. SERVLET ENGINE. File System Database. Web Browser. Servlet. Servlet. Servlet.

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Servlets

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  1. Servlets

  2. Servlets • - Java technology for Common Gateway Interface (CGI) programming. • - It is a Java class that dynamically extends the function of a web server.

  3. WEB SERVER SERVLET ENGINE File System Database Web Browser Servlet Servlet Servlet

  4. Servlets vs Traditional CGI Programs • Servlets are efficient. No new process is started for each HTTP request. • Servlets are convenient. Extensive Java infrastructure is already available. • Servlets are powerful. It has full access to Java’s advanced features such as networking, security, database access, etc. • Servlets are portable. • Servlets are Secure. • Servlets are inexpensive to implement.

  5. Compiling Servlets • Tomcat Standard Installation Directories • Standard location for servlets: Tomcat/webapps/ROOT/WEB-INF/classes • Alternate location for servlet classes: Tomcat/classes • Location of JAR files containing classes: Tomcat/lib • To compile servlets: • javac ServletName.java

  6. Servlet Events • init() method • destroy() method • service() method • Request are handled in here. • Objects involved: • Request object (implements the ServletRequest interface). • Response object(implements the ServletResponse interface).

  7. Servlet Generating Plain Text import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloSample extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { PrintWriter out = response.getWriter(); out.println("HELLO WORLD in PLAIN TEXT"); } } /* Make sure you compile this in a path specified in the CLASSPATH such as C:\Tomcat\webapps\ROOT\Web-INF\classes */

  8. A Web Page Invoking the Servlet <html> <head> <title>Testing a Simple Servlet</title> </head> <body > <p><H1><a href="/servlet/HelloSample"> Click ME!</a></H1> </body> </html>

  9. Servlet Generating an HTML Page import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloSample extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType(“text/html”); PrintWriter out = response.getWriter(); out.println(”<HTML>\n <HEAD> <TITLE>” + “SAMPLE HTML PAGE” </HEAD>\n” + “<BODY> \n” + “<H1> HELLO HTML</H1>\n” + “</BODY> </HTML>”); } }

  10. package myServlets; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class RandomNum extends HttpServlet { private int [] numbers = new int[6]; public void init( ) throws ServletException { for(int i=0; i<numbers.length; i++) numbers[i] = (int) (Math.random() * 100); } public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<HTML>\n<HEAD><TITLE>Random Numbers" + "</TITLE></HEAD>\n <BODY>\n" + "<H1> LOTTERY NUMBERS ARE: </H1>\n<OL>"); for (int i=0; i < numbers.length; i++) out.println("<LI>" + numbers[i]); out.println("</OL> \n </BODY></HTML>"); } }

  11. Form Data Handling GET - form data is attached to the end of the URL after the question mark. http://process.cgi?name=john+doe&date=12-20-99 POST - form data is sent to the server on separate lines. Parsing this form data is handled by the getParameter( ) method of the HttpServletRequest. This method returns a String data type. String PersonName = Request.getParameter(“name”);

  12. Servlet Handling Form Data import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class FormDataSample extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType(“text/html”); PrintWriter out = response.getWriter(); out.println(”<HTML>\n <HEAD> <TITLE>” + “SAMPLE FORM DATA” </HEAD>\n” + “<BODY> \n” + “<H1> HELLO “ + request.getParameter(“name”) + “</H1>\n” + “</BODY> </HTML>”); } }

  13. The Web Page Using Form <html> <head> <title>A Simple Form</title> </head> <body > <form action=“/servlet/FormDataSample”> <center> name:<input type=“TEXT” name=“name”> <br> <input type=“submit” > </center> </form> </body> </html>

  14. <HTML> <HEAD><TITLE> ORDER PROCESSING</TITLE></HEAD> <BODY BGCOLOR="lightsalmon"> <H1 align="center"> COMPLETE TRANSACTION INFORMATION </H1><br> <Form action="/servlet/myServlets.ProcessData" METHOD="Post"> Part Number: <select name="ONUM"> <option value="1010"> 101010 <option value="2020"> 202020 <option value="3030"> 303030 <option value="4040"> 404040 </select> &nbsp; &nbsp Quantity: <input type="text" name="QTY"> &nbsp Unit Price($): <input type="text" name="PRICE"><br> <HR> First Name: <input type="text" name="FNAME"> &nbsp Last Name: <input type="text" name="LNAME"> &nbsp Middle Initial: <input type="text" name="MNAME"><br> <br>Shipping Address: <textarea name="ADDRESS" ROWS=3 COLS=30> </Textarea><br><br> Credit Card: <br> &nbsp; &nbsp <input type="radio" name="card" value="V"> Visa &nbsp <input type="radio" name="card" value="M"> Mastercard &nbsp <input type="radio" name="card" value="D"> Discover &nbsp <input type="radio" name="card" value="A"> American Express &nbsp <input type="radio" name="card" value="B"> BankCard &nbsp <br> Credit Card number: <input type="password" name="CARDNUM"><br> <Center> <input type="SUBMIT" value="SUBMIT"> <input type="RESET" value="CLEAR"> </Center><HR> Please let us know by checking the proper box: <br> &nbsp <input type="checkbox" name="CHKEMAIL"> Email Notification? <br> &nbsp <input type="checkbox" name="CHKWAIT"> Wait for complete order before shipment?<br> &nbsp <input type="checkbox" name="CHKPROMO"> Inform you of Promotions? <br> </form> </body> </html>

  15. package myServlets; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.util.*; public class ProcessData extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter( ); out.println("<HTML>\n<HEAD><TITLE>INPUT PARAMETERS" + "</TITLE></HEAD>\n <BODY>\n" + "<H1> PARAMETERS ARE: </H1>\n"); Enumeration PNames = request.getParameterNames( ); while (PNames.hasMoreElements( )) { String PNameVal = (String) PNames.nextElement( ); String PValues= request.getParameter(PNameVal); String TString = "CARDNUM"; if (PNameVal.equals(TString)) out.println(PNameVal + " = ********* <BR>"); else out.println(PNameVal + " = " + PValues + "<BR>"); }// end of while out.println(" \n </BODY></HTML>"); }// end of doGet public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { doGet(request, response); } }

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