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servlets and jsp

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Transcript

  • 1. J2EE
  • 2. Introduction ● Q. What is J2EE ? Java platform to developing enterprise web application
  • 3. Basic Architecture
  • 4. Description ● J2EE architecture : 3 tier – Client Tier ( Web tier) ● – Business Tier ● – The Presentation layer on the client side includes j2ee componenets such as jsp,jsf etc Components containing business logic of the application such as Enterprise Beans. Database Tier ● This tier contains the persistence API of the application so as to talk to database
  • 5. Java Web Components ● Servlet ● Jsp ( Java Server Pages ) ● Jstl (Jsp Standard Tag Library) ● Jsf ( Java Server Faces )
  • 6. Servlet ● Extends web server's functionality ● Respond to Request from client ● Used to generate dynamic response ● Usually responses in HTML or Xml format ● Most often used with HTTP protocol
  • 7. Functioning of Servlet ● ● ● Process or Store data that was submitted by HTML forms Provide dynamic content such as the result of a database query Manage State information (in case of stateless HTTP protocol)
  • 8. Packages (imports) for Servlet ● java.io.*; – ● javax.servlet – ● Input and Output package (eg. Out.println) Contains interaction logic between web container and servlet javax.servlet.http – Contains Http specific logic
  • 9. ● javax.servlet.http.HttpServletRequest; ● javax.servlet.http.HttpServletRespons
  • 10. Servlet Skeleton ● Imports ● Public classname extends HttpServlet – Public void init() ● – Public void Service() ● – { /* Initialization goes here */ } {/* Business logic goes here */ } Public void destroy() ● {/* Free resources here */}
  • 11. Lifecycle ● Loaded and Instantiated ● Initialization ● Servicing the request ● Destroying the request
  • 12. ● Loaded and instantiated – ● Container loads servlet during startup or when the request is made. After loading the servlet , the container creates the instance of the servlet when the first request come for service , Initialization – After creating the instance the container calls init() method. The init method is called only once in servlets lifetime. Initialization logic goes here
  • 13. ● Servicing the request – After successful initialization , servlet will be available to serve the request. Servlet creates separate thread for each request – Service() method is called to serve the request in short service method contains the business logic
  • 14. ● Destroying the servlet – If the servlet is no longer needed , the servlet container calls the destroy() method. – Like the init() method destroy() method also get called only once in servlet's lifetime – Destroy() method releases all the resources which were acquired previously
  • 15. JSP (Java Server Pages) ● Jsp is a component which generates dynamic contents ● Jsp is a server-side technology ● Extension : .jsp ● Jsp usually consist of two components – Static Data ● – Can be expressed in any text based format such as HTML JSP elements ● Jsp tags , which can generates dynamic contents
  • 16. JSP Components ● Declaration tag ● Scriptlet tag ● Expression tag ● Directive tag ● Action tag
  • 17. ● Declaration tag: – Declaration is used to declare and define java variables and methods inside your jsp – They are initialized when the jsp page is initialized – The scope of the declared variables or methods is within the jsp page – Syntax : <%! int a = 10; %>
  • 18. Declaration Example : <html> <body> <%! int value = 10; %> Hello World!<%= value %> </body> </html>
  • 19. ● Scriptlet tag: – Scriptlets are block of java code – You can write any number of java code inside your jsp using scriptlet – Syntax : <% ( Java Code ) %>
  • 20. Scriptlet Example : <html> <body> Hello World! <% out.println("Helloworld"); %> </body> </html>
  • 21. ● Expression tag: – The code placed inside expression tag is printed (output) , so there is no need to write out.println() – Mainly used to print values of variables and methods – Syntax : <%= (variable or method) %>
  • 22. Expression Example : <html> <body> <%! int value = 10; %> Hello World! <%= value %> </body> </html>
  • 23. ● Directive tag: – Jsp directive provide directions and instructions to the container , how to handle certain jsp processing – There are 3 types of directives ● ● ● Page directive Include directive Taglib directive
  • 24. – Page directive ● ● ● Page directive is used to provide information about the page Example : <%@page language="java" %> Here language is an attribute of the page directive
  • 25. – Include directive ● ● ● Include is used to include a jsp file in the jsp page Example : <%@ include file="/header.jsp" %> File is an attribute which specifies which file need to include
  • 26. – Taglib directive ● ● ● Taglib directive is used to use the custom tags in the jsp page ( custom tags allow us to define our own tags ) Example : <%@ taglib uri="tlds/taglib.tld" prefix="mytag" %>
  • 27. ● Action tag: – The action tag basically are used to control the flow between pages and to use Java Beans
  • 28. – Some of the action tags are ● ● ● ● ● ● ● ● Jsp:forward Jsp:include Jsp:useBean Jsp:setProperty Jsp:getPropery Jsp:plugin Jsp:param Jsp:fallback