HTTP, JSP, and AJAX.pdf

1. Outline Introduction Overview WEB 1.0 vs WEB 2.0 HTTP, CGI, Web Application Model HTTP Common Gateway Interface (CGI) Web Application Model Summary Servlet & JSP Servlet Java Server Pages AJAX Using AJAX Summary Resources

2. Java Web Application Model Web Server Database Server Side Apps Web Application Container Web Application /app1 servlet servlet servlet Web Application /app2 servlet servlet servlet Server side Service Invocation request handling client request/response Figure: Java Web Application Model

3. Java Web Application Model There are several levels of scope, where each one has its parameters: I Container: system-wide configuration I Application: application configuration and parameters I Servlet: servlet information and parameters I Page: information related with a JSP I Session: session information can cross pages and servlets, session can be used to store objects Each level is modeled by a Java class or interface. (Implicit objects in JSP)

4. Interface javax.servlet.Servlet This interface defines methods to initialize a servlet, to service requests, and to remove a servlet from the server: I The servlet is constructed, then initialized with the init method. I Any calls from clients to the service method are handled. I The servlet is taken out of service, then destroyed with the destroy method, then garbage collected and finalized. In addition to the life-cycle methods, this interface provides the getServletConfig method, which the servlet can use to get any startup information, and the getServletInfo method, which allows the servlet to return basic information about itself, such as author, version, and copyright.

5. Abstract Class javax.servlet.GenericServlet The abstract class GenericServlet defines a generic, protocol-independent servlet. I It implements the Servlet and ServletConfig interface. I It provides simple versions of the lifecycle methods init and destroy and of the methods in the ServletConfig interface. GenericServlet also implements the log method, declared in the ServletContext interface. To write a generic servlet, you need only override the abstract service method. HttpServlet is a subclass of GenericServlet using HTTP protocol.

6. Abstract class javax.servlet.http.HttpServlet The abstract class HttpServlet is designed to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these: I doGet, if the servlet supports HTTP GET requests I doPost, for HTTP POST requests I doPut, for HTTP PUT requests I doDelete, for HTTP DELETE requests I init and destroy, to manage resources that are held for the life of the servlet I getServletInfo, which the servlet uses to provide information about itself

12. Writing a HttpServlet A Servlet which returns ”Hello World” to the browser import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); out.println("Hello World"); } public String getServletInfo() { return "Hello world example for PINFO"; } }

13. Writing a HttpServlet II Return HTML content import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); // set HTTP response content type PrintWriter out = response.getWriter(); out.println("<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 " + "Transitional//EN">n" + "<HTML>n" + "<HEAD><TITLE>Hello WWW</TITLE></HEAD>n" + "<BODY>n" + "<H1>Hello WWW</H1>n" + "</BODY></HTML>"); } public String getServletInfo() { return "Hello world example for PINFO"; } }

14. Get the value of the request parameter HttpServletRequest class Request URL: http://localhost:8080/list.jsp?category=pinfo05 public void doGet(HttpServletRequest request, HttpServletResponse response) throws ... { ... String cat = request.getParameter("category"); ...} cat will have value ”pinfo05”. It works for both GET and POST requests. Two important classes: HttpServletRequest contains information about the request; HttpServletResponse is used to generate HTTP response.

15. Java Server Pages Java Server Pages A way of creating dynamic pages with Java and HTML. Principle: Java for application logic, HTML for presentation. JSP uses HTML for page rendering, and provides several ways to use Java components: I Scriptlet: Java codes enclosed by <% and %> I Taglib: customized JSP tags I Using JavaBeans JSP are translated into Java servlets before they are compiled by the Web application container. HttpServletRequest and HttpServletResponse are implicit objects in JSP.

16. Implicit Objects in Java Server Page The following variables can be directly used in JSP: I page: jsp.HttpJspPage : Page’s servlet instance I config: ServletConfig : Servlet configuration information I pageContext: jsp.pageContext : Provides access to all the namespaces associated with a JSP page and access to several page attributes I request: http.HttpServletRequest : Data included with the HTTP Request I response: http.HttpServletResponse : HTTP Response data, e.g. cookies I out: jsp.JspWriter : Output stream for page context I session: http.HttpSession : User specific session data I application: ServletContext : Data shared by all application pages

25. Asynchronous JavaScript And XML (AJAX) AJAX incorporates several technologies: I standards-based presentation using XHTML and CSS; I dynamic display and interaction using the Document Object Model; I data interchange and manipulation using XML and XSLT; I asynchronous data retrieval using XMLHttpRequest; I and JavaScript binding everything together. www.w3schools.com provides tutorials for XHTML, CSS, DOM, XML, AJAX, JavaScript etc.

30. AJAX: Connect HTML with JavaScript Capture Events on HTML pages I Mouse event (with elements): mouse down, mouse up, mouse move, mouse over ... I Keyboard event: key pressed ... I Form: submitted ... I Timer etc. Example: Call the getListByCategory function when the mouse is moved over the hyper linked text, and call the function cleanTable when the moused is moved out the link. <a href="/" onmouseover="getListByCategory()" onmouseout="clearTable()">Show Member List</a>

31. AJAX: Create XMLHttpRequest Object This function will create an XMLHttpRequest object and send a GET request to the server page http://pinfo.unige.ch:8080/Member/list.jsp with parameter category with value pinfo05. Send a HTTP request via XMLHttpRequest Object: function getListByCategory() { var req = false; var self = this; var url = "http://pinfo.unige.ch:8080/Member/list.jsp?category=pinfo05"; if (window.XMLHttpRequest) { self.req = new XMLHttpRequest(); // for Firefox and other browsers } else if (window.ActiveXObject) { self.req = new ActiveXObject("Microsoft.XMLHTTP"); // for IE browser } // when the request is finished, call this function self.req.onreadystatechange = processRequest; self.req.open("GET", url, true); // it is a GET request self.req.send(null); // send the request } Note that the implementation of XMLHttpRequest is different from one browser to another.

32. AJAX: Handling Asynchronous Response A node is tagged with id ”result” in the HTML document <div id=result></div> The function processRequest is called when the XMLHttpRequest is finished (asynchronous response). function processRequest() { // check the request state is "complete" if (req.readyState == 4 || req.readyState == "complete") { if (req.status == 200) { updatepage(self.req.responseText); } else { alert("Not able to retrieve member list"); } } } // Just set the content of note with id "result" with the input parameter // Other DOM and XML operations are possible, here it is simplified. function updatepage(str) { document.getElementById("result").innerHTML = str; }

33. AJAX: Web Application Model Figure: AJAX Web Application Model

34. AJAX: Interactions Figure: AJAX Interactions

36. Summary I Web Application Model: relations between client, Web server, server side application, and web application. The Application Container model is mature. I JSP and Servlets provide server side programming facilities: reusability, manageability, security etc. I AJAX provides a standard solution for client/server interaction: XML based, Asynchronous, no page refresh needed. It is the most used technology in WEB 2.0. I AJAX is the complement for the presentation layer of Web applications with JSP: JSP provides services, AJAX use these services, messages are in XML, communication via HTTP. I WEB 2.0 is more than AJAX.

43. Servlet, JSP Specifications: I Java Servlet Specifications I JSP Technology Tutorial: I Basic Servlets: http://www.apl.jhu.edu/ hall/java/Servlet-Tutorial/ I MoreServlets Book & Tutorials: Servlet, JSP, Taglib, Struts, AJAX

44. AJAX, WEB 2.0 AJAX: I Ajax: A New Approach to Web Applications I AJAX: Getting Started, mozilla developer center I Top 10 Ajax Applications I AJAX Tutorial I AJAX Login System Demo I Guide to Using AJAX and XMLHttpRequest I Ajaxian WEB 2.0 I O’Reilly: What Is Web 2.0 I The Best Web 2.0 Software of 2005 I Writly I Google Earth

HTTP, JSP, and AJAX.pdf

Recommended

More Related Content

Similar to HTTP, JSP, and AJAX.pdf (20)

More from Arumugam90 (20)

Recently uploaded (20)

HTTP, JSP, and AJAX.pdf