1 / 42

Java Servlets

Java Servlets. What Are Servlets?. Basically, a java program that runs on the server Creates dynamic web pages. What Do They Do?. Handle data/requests sent by users (clients) Create and format results Send results back to user. Who Uses Servlets?.

becky
Download Presentation

Java Servlets

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Java Servlets

  2. What Are Servlets? • Basically, a java program that runs on the server • Creates dynamic web pages

  3. What Do They Do? • Handle data/requests sent by users (clients) • Create and format results • Send results back to user

  4. Who Uses Servlets? • Servlets are useful in many business oriented websites • … and MANY others

  5. History • Dynamic websites were often created with CGI • CGI: Common Gateway Interface • Poor solution to today’s needs • A better solution was needed

  6. Servlets vs. CGI CGI • Servlet Advantages • Efficient • Single lightweight java thread handles multiple requests • Optimizations such as computation caching and keeping connections to databases open • Convenient • Many programmers today already know java • Powerful • Can talk directly to the web server • Share data with other servlets • Maintain data from request to request • Portable • Java is supported by every major web browser (through plugins) • Inexpensive • Adding servlet support to a server is cheap or free

  7. Servlets vs. CGI • CGI Advantages • CGI scripts can be written in any language • Does not depend on servlet-enabled server

  8. What Servlets Need • JavaServer Web Development Kit (JSWDK) • Servlet capable server • Java Server Pages (JSP) • Servlet code

  9. Java Server Web Development Kit • JSWDK • Small, stand-alone server for testing servlets and JSP pages • The J2EE SDK • Includes Java Servlets 2.4

  10. Servlet capable server Apache • Popular, open-source server • Tomcat • A “servlet container” used with Apache Other servers are available

  11. Java Server Pages • Lets you mix regular, static HTML pages with dynamically-generated HTML • Does not extend functionality of Servlets • Allows you to separate “look” of the site from the dynamic “content” • Webpage designers create the HTML • Servlet programmers create the dynamic content • Changes in HTML don’t effect servlets

  12. <head> </head> <body> <% // jsp sample code out.println(" JSP, ASP, CF, PHP - you name it, we support it!"); %> </body> </html> <html> <head> </head> <body> <b> JSP, ASP, CF, PHP - you name it, we support it! </b> </body> </html> </font>

  13. <head> </head> <body> <% // jsp sample code out.println(" JSP, ASP, CF, PHP - you name it, we support it!"); %> </body> </html> <html> <head> </head> <body> <b> JSP, ASP, CF, PHP - you name it, we support it! </b> </body> </html> </font>

  14. <head> </head> <body> <% // jsp sample code out.println(" JSP, ASP, CF, PHP - you name it, we support it!"); %> </body> </html> <html> <head> </head> <body> <b> JSP, ASP, CF, PHP - you name it, we support it! </b> </body> </html> </font>

  15. <head> </head> <body> <% // jsp sample code out.println(" JSP, ASP, CF, PHP - you name it, we support it!"); %> </body> </html> <html> <head> </head> <body> <b> JSP, ASP, CF, PHP - you name it, we support it! </b> </body> </html> </font>

  16. Servlet Code • Written in standard Java • Implement the javax.servlet.Servlet interface

  17. package servlet_tutorials.PhoneBook;import javax.servlet.*;import javax.servlet.http.*;import java.io.*;import java.util.*; import java.sql.*; import java.net.*;public class SearchPhoneBookServlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { String query = null; String where = null; String firstname = null; String lastname = null; ResultSet rs = null;res.setContentType("text/html"); PrintWriter out = res.getWriter();// check which if any fields in the submitted form are empty if (req.getParameter("FirstName").length() > 0) firstname = req.getParameter("FirstName"); else firstname = null;}

  18. Main Concepts of Servlet Programming • Life Cycle • Client Interaction • Saving State • Servlet Communication • Calling Servlets • Request Attributes and Resources • Multithreading

  19. Life Cycle • Initialize • Service • Destroy

  20. Life Cycle: Initialize • Servlet is created when servlet container receives a request from the client • Init() method is called only once

  21. Life Cycle: Service • Any requests will be forwarded to the service() method • doGet() • doPost() • doDelete() • doOptions() • doPut() • doTrace()

  22. Life Cycle: Destroy • destroy() method is called only once • Occurs when • Application is stopped • Servlet container shuts down • Allows resources to be freed

  23. Client Interaction • Request • Client (browser) sends a request containing • Request line (method type, URL, protocol) • Header variables (optional) • Message body (optional) • Response • Sent by server to client • response line (server protocol and status code) • header variables (server and response information) • message body (response, such as HTML)

  24. Servlets • Thin clients (minimize download) • Java all “server side” Client Server

  25. Saving State • Session Tracking • A mechanism that servlets use to maintain state about a series of requests from the same user (browser) across some period of time. • Cookies • A mechanism that a servlet uses to have clients hold a small amount of state-information associated with the user.

  26. Servlet Communication • To satisfy client requests, servlets sometimes need to access network resources: other servlets, HTML pages, objects shared among servlets at the same server, and so on.

  27. Calling Servlets • Typing a servlet URL into a browser window • Servlets can be called directly by typing their URL into a browser's location window. • Calling a servlet from within an HTML page • Servlet URLs can be used in HTML tags, where a URL for a CGI-bin script or file URL might be found.

  28. Request Attributes and Resources • Request Attributes • getAttribute • getAttributeNames • setAttribute • Request Resources - gives you access to external resources • getResource • getResourceAsStream

  29. Multithreading • Concurrent requests for a servlet are handled by separate threads executing the corresponding request processing method (e.g. doGet or doPost). It's therefore important that these methods are thread safe. • The easiest way to guarantee that the code is thread safe is to avoid instance variables altogether and instead use synchronized blocks.

  30. Simple Counter Example import java.io.*; import javax.servlet.*; import javax.servlet.http.*; • public class SimpleCounter extends HttpServlet { • int count = 0; • public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { • res.setContentType("text/plain"); • PrintWriter out = res.getWriter(); • count++; • out.println("This servlet has been accessed " + count + " times since loading"); • } • }

  31. MultiThread Problems • Problem - Synchronization between threads count++; // by thread1 count++; // by thread2 out.println.. // by thread1 out.println.. // by thread2 Two Requests will get the same value of counter • Solution - Use Synchronized Block! • Synchronized Block • Lock(Monitor)

  32. Better Approach • The approach would be to synchronize only the section of code that needs to be executed automically: PrintWriter out = res.getWriter(); synchronized(this) {    count++;     out.println("This servlet has been accessed " +              count + "times since loading");}This reduces the amount of time the servlet spends in its synchronized block, and still maintains a consistent count.

  33. Example: On-line Phone Book • Design

  34. Example: On-line Phone Book

  35. Search Form Java server Page Search_phone_book.jsp <html><head> <title>Search Phonebook</title> </head> <body bgcolor="#FFFFFF"> <p><b>Search Company Phone Book</b></p> <form name="form1" method="get" action="servlet/servlet_tutorials.PhoneBook.SearchPhoneBookServlet"> <table border="0" cellspacing="0" cellpadding="6"> <tr> <td >Search by</td> <td></td> </tr> <tr> <td><b>First Name </b></td> <td> <input type="text" name="FirstName"> AND/OR</td> </tr> <tr> <td ><b>Last Name</b></td> <td ><input type="text" name="LastName"></td> </tr> <tr> <td ></td> <td ><input type="submit" name="Submit" value="Submit"></td> </tr> </table></form></body></html>

  36. Example: On-line Phone Book

  37. Display Results Java Server Page Display_search_results.jsp <html><%@page import ="java.sql.*" %><jsp:useBean id="phone" class="servlet_tutorials.PhoneBook.PhoneBookBean"/> <%@ page buffer=35 %><%@ page errorPage="error.jsp" %><html><head><title>Phone Book Search Results</title><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head><body bgcolor="#FFFFFF"> <b>Search Results</b> <p> <% String q = request.getParameter("query"); ResultSet rs = phone.getResultSet(q); %><% if (rs.wasNull()) { %> "NO RESULTS FOUND" <% } else %><table> <tr> <td> <div align="center">First Name</b></div> </td> <td> <div align="center">Last Name</font></b></div> </td> <td> <div align="center">Phone Number</font></b></div> </td> <td> <div align="center">Email</font></b></div> </td> </tr><% while(rs.next()) { %> <tr> <td><%= rs.getString("first_name") %></td> <td><%= rs.getString("last_name") %></td> <td><%= rs.getString("phone_number") %></td> <td><%= rs.getString("e_mail") %></td> </tr> <% } %></table>

  38. Servlet

  39. Java Bean & Database linked

  40. Conclusion

  41. Questions? Comments?

  42. References • http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/Servlet-Tutorial-Overview.html • www.cis.upenn.edu/~matuszek/ cit597-2004/Lectures/21-servlets.ppt • http://learning.unl.ac.uk/im269/lectures/week6servletsp1.ppt • http://java.sun.com/docs/books/tutorialNB/download/tut-servlets.zip • http://www.webdevelopersjournal.com/articles/intro_to_servlets.html

More Related