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Lecture 10 Object Oriented Programming in Java

Lecture 10 Object Oriented Programming in Java. Advanced Topics Servlets. Today’s Lecture. Trail: Servlets Lesson:overview,Cient Interaction, LifeCycle,... http://web2.java.sun.com/docs/books/tutorial/servlets/index.html Additional Link

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Lecture 10 Object Oriented Programming in Java

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  1. Lecture 10Object Oriented Programming in Java Advanced Topics Servlets Object Oriented Programming in Java (95-707)Advanced Topics

  2. Today’s Lecture • Trail: Servlets • Lesson:overview,Cient Interaction, LifeCycle,... • http://web2.java.sun.com/docs/books/tutorial/servlets/index.html • Additional Link http://developer.java.sun.com/developer/onlineTraining/Servlets/Fundamentals/introduction.html Object Oriented Programming in Java (95-707)Advanced Topics

  3. Servlet Architecture Web server with servlet engine Client Browser 2: call servlet with request info 1: send http request HTTP Servlet 5: send HTTP response 4: return information from servlet engine 3: perform logic Object Oriented Programming in Java (95-707)Advanced Topics

  4. 1: send HTTP request • Handled by regular html tags • examples: • simple http://localhost:8080/servlet/snoop • with parameters http://localhost:8080/servlet/snoop?username=alain • from a form post <form action=“/servlet/snoop” method=“post”> <input type="text" name="username" value=""> <input type="text" name=”password" value=""> </form> Object Oriented Programming in Java (95-707)Advanced Topics

  5. 2: call servlet with request info • Handled by the web server • transparent to the developer Object Oriented Programming in Java (95-707)Advanced Topics

  6. 3: perform logic • Handled by a custom java class which inherits from the Servlet class Object Oriented Programming in Java (95-707)Advanced Topics

  7. 4: return response from servlet engine • Handled by the web server • transparent to the developer Object Oriented Programming in Java (95-707)Advanced Topics

  8. 5: final step • The browser renders the html page which is returned • In this class we will only deal with HTML, but others types could be returned by servlets • I.e.: audio, images, ... Object Oriented Programming in Java (95-707)Advanced Topics

  9. Overall Servlet API • base class is HttpServlet • APIs to: • initialize servlets • receive http requests • retrieve information on the request • send a response to the browser • maintain session across multiple invocations (remember that HTTP is session-less) Object Oriented Programming in Java (95-707)Advanced Topics

  10. Base Class: HttpServlet Example from HelloWorldServlet: import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorldServlet extends HttpServlet { … } Object Oriented Programming in Java (95-707)Advanced Topics

  11. Initialization of Servlet • Example from PhoneServlet.java public class PhoneServlet extends HttpServlet { private Hashtable phones = new Hashtable(); private String dataFilePath = "phonelist"; // Public Methods public void init(ServletConfig conf) throws ServletException { super.init(conf); String param = getInitParameter("phonelist"); if (param != null) { dataFilePath = param; } ... readFromFile(); } } Object Oriented Programming in Java (95-707)Advanced Topics

  12. HTTP GET and POST • Example from PhoneServlet: public class PhoneServlet extends HttpServlet { public void init(ServletConfig conf) throws ServletException { ... } public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { ... } public void doPost(HttpServletRequest req, HttpServletResponse res) throws IOException { ... } } • doGet is called when we have HTTP GET • doPost is called when we have HTTP POST Object Oriented Programming in Java (95-707)Advanced Topics

  13. Inside doGet and doPost • Three usual steps: • read request data such as input parameters • set response headers • length, type • write the response data Object Oriented Programming in Java (95-707)Advanced Topics

  14. Get Request Data and Parameters • Example from PhoneServlet public void doPost (HttpServletRequest req, HttpServletResponse res)throws IOException { ... String name, number, opcode; name = req.getParameter("name"); number = req.getParameter("number"); opcode = req.getParameter("opcode"); ... } • <form action=“/servlet/PhoneServlet” method=“post”> • <input type="text" name=”name" value=""> • <input type="text" name=”number" value=""> • <input type="text" name=”oncoder" value=""> • </form> Object Oriented Programming in Java (95-707)Advanced Topics

  15. Set Response Headers • Example from PhoneServlet: public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); ServletOutputStream out = res.getOutputStream(); String title = "Phones"; ... out.println("<HEAD><TITLE> Phone Servlet Output </TITLE></HEAD>"); out.println("<BODY BGCOLOR=\"#FFFFFF\">"); out.println("<h1>Phone Records</h1>"); out.println("<p>"); ... ) Object Oriented Programming in Java (95-707)Advanced Topics

  16. Create response • Example from PhoneServlet: public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); ServletOutputStream out = res.getOutputStream(); String title = "Phones"; ... out.println("<HEAD><TITLE> Phone Servlet Output </TITLE></HEAD>"); out.println("<BODY BGCOLOR=\"#FFFFFF\">"); out.println("<h1>Phone Records</h1>"); out.println("<p>"); ... ) Object Oriented Programming in Java (95-707)Advanced Topics

  17. HTTP protocol is session-less • HTTP protocol is session-less • between two requests the web server does not remember the caller • protocol is as follows: • browser connects to HTTP server • browser makes a request for a web resource • web server looks for the resource • web server forwards the resource to the browser • web server disconnects the browser Object Oriented Programming in Java (95-707)Advanced Topics

  18. Sessions with Servlets • The servlet engine fills-in the gap and provides a way to keep a session across multiple requests to a web server • Mechanism is handled by the servlet engine “on demand” by the servlets • The base class is HttpSession Object Oriented Programming in Java (95-707)Advanced Topics

  19. HttpSession • Example from SessionServlet.java public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { HttpSession session = req.getSession(true); ... //Here's the meat Integer ival = (Integer) session.getValue("sessiontest.counter"); if (ival==null) ival = new Integer(1); else ival = new Integer(ival.intValue() + 1); session.putValue("sessiontest.counter", ival); ... ) Object Oriented Programming in Java (95-707)Advanced Topics

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