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Java Server Pages

Java Server Pages. JSP. Concept: Server-side programming . CGI scripts servlet Java program that runs on webserver Called from html page Follows Sun servlet standard JavaServer page (JSP) Contains html and Java or JavaScript Compiled into a servlet and run on server. JSP is servlet.

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Java Server Pages

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  1. Java Server Pages JSP

  2. Concept:Server-side programming • CGI scripts • servlet • Java program that runs on webserver • Called from html page • Follows Sun servlet standard • JavaServer page (JSP) • Contains html and • Java or JavaScript • Compiled into a servlet and run on server

  3. JSP is servlet • follows request-response model • loaded into webserver • webserver manages instance • typical logic • examine request: • parameters, session, cookies, context • produce response • add to output stream

  4. JSP page • stored with extension “.jsp” • contains • html • JSP scripting elements • JSP directives • JSP actions • JSP comment • <%-- --%>

  5. JSP scripting elements • declaration • <%! %> • expression • <%= %> • scriptlet • <% %>

  6. JSP declaration • placed into servlet outside of service method • <%! int accessCount = 0; %>

  7. JSP expression • expression is evaluated and placed into output This page has been accessed <%= accessCount %> times

  8. JSP scriptlet • code that is inserted into service method • <% accessCount += 1; %>

  9. first JSP example <html> <head><title>Very Simple JSP</title></head> <body> <h1>Very Simple JSP</h1> <%! int accessCount = 0; %> This page has been accessed <%= accessCount %> times <% accessCount += 1; %> </body> </html>

  10. Run from Internet explorer

  11. JSP directives • control overall structure of servlet • include • used to include another file • <%@ include file=“relative URL” %> • URL may start with “/”

  12. JSP directive: page • has attributes • import • to add import statements to servlet • <%@ page import=“java.util.*” %> • content-type • isThreadSafe • value “true” is default • “false” makes servlet implement SingleThreadModel

  13. JSP page directive:more attributes • session • value “true” is default • “false” disables session management • buffer="sizekb|none“ • specifies the buffer size for the JspWriter out • autoflush="true|false” • extends="package.class” • info="message” • errorPage="url” • isErrorPage="true|false” • language="java"

  14. Predefined variables • request • instance of HttpServletRequest • ex: request.getParameter(“username); • response • instance of HttpServletResponse • ex: response.addCookie(myCookie);

  15. Predefined variables • out • instance of JSPWriter • buffered version of output stream • ex: out.println(“hello world”); • same as html text outside of <% … %>

  16. Predefined variables • session • instance of HttpSession • only available if session attribute of <%@ page %> directive is true • ex: session.setAttribte(“user”, “John Doe”); • ex: name = (String) session.getAttribute(“user”);

  17. Predefined variables • application • instance of HttpContext • ex: application.setAttribute(“user”, “John Doe”); • ex: name = (String)application.getAttribute(“user); • config • instance of HttpConfig • page • same as “this” in Java

  18. JSP example: second.jsp <html><head><title>Session JSP</title></head><body> <h1>Welcome to our World</h1> <%@ page session="true" %> <form action="second.jsp"> <% if (session.isNew()) { %> Enter your ID: <input type="text" name="username"> <% } else { String name = request.getParameter("username"); if (name == null) name = (String)session.getAttribute("user"); else session.setAttribute("user", name); %> Welcome back <%= name %> <% } %> <input type="submit"></form> </body></html>

  19. Run and observe JSP

  20. JSP actions • jsp:include • include a file at the time the page is requested • jsp:forward • forward the requester to a new page • jsp:useBean • find or instantiate a JavaBean • jsp:setProperty • set the property of a JavaBean • jsp:getProperty • insert the property of a JavaBean into the output • jsp:plugin

  21. jsp:include action <jsp:include page="relative URL" flush="true" /> • inserts the file at the time the JSP page is translated into a servlet • similar to “include” method of RequestDispatcher

  22. jsp:forward action <jsp:forward page="relative URL" /> • forwards the request to another page • similar to “forward” method of RequestDispatcher • examples: <jsp:forward page="errorReporter.jsp" />

  23. Exercise: shopping cart

  24. Exercise: shopping cart

  25. Greeting.html <html><head> <title>Shopping cart example</title></head> <body><h1>Welcome to the Mini Store</h1> <form action="MiniStore.jsp" method="post"> Please select one or more of our products:<br> <select name="products" multiple> <option>product 1 <option>product 2 <option>product 3 <option>product 4 <option>product 5 <option>product 6 </select> <input type="submit"> </form> </body></html>

  26. MiniStore.jsp (1/3) <%@ page import="java.util.*" %> <HTML><BODY> <% if (session.isNew()) { %> <h1>Welcome Newcomer</h1> <% } else { %> <h1>Welcome Back</h1> <% } %>

  27. MiniStore.jsp (2/3) <% Vector list = (Vector) session.getAttribute("cart"); if (list == null) list = new Vector(); String products[] = request.getParameterValues("products"); if (products != null) for (int i = 0; i < products.length; i++) list.addElement(products[i]); session.setAttribute("cart", list); %>

  28. MiniStore.jsp (3/3) <H2>Thanks for your selection:</H2> <TABLE><TR><TH>Product</TH></TR> <% Enumeration all = list.elements(); while (all.hasMoreElements()) out.println("<TR><TD>" + all.nextElement() +"</TD>"); %> </tr></table> <jsp:include page="continue.html"/> </body></html>

  29. continue.html <form action="Greeting.html"> <input type="submit" value="Continue Shopping"> </form>

  30. jsp:useBean action <jsp:useBean id="name" class="package.class" /> • instantiates an object of the specified class • binds it to a variable with id “name” • variable can be used to invoke bean methods or to handle its properties • bean can be associated with scope

  31. jsp:useBean actionscope attribute <jsp:useBean id="name" class="package.class" scope=“value”/> • values can be • page (default) • request • session • application • makes bean accessible within scope

  32. jsp:setProperty action <jsp:setProperty name="orderBean" property="numberOfItems" value=“21" /> <jsp:setProperty name="orderBean" property="numberOfItems" param="numItems" /> • sets value of bean property

  33. jsp:getProperty action <jsp:getProperty name="itemBean" property="numItems" /> • value of bean property is returned

  34. Bean example package jspexamples; public class Counter { private int value = 0; public int getValue() { return value; } public void setValue(int newValue) { value = newValue; } }

  35. JSP example <html> <head> <title>Bean JSP example</title> </head> <body> <jsp:useBean id="counter" class="jspexamples.Counter"/> <jsp:setProperty name="counter" property="value" value="10"/> Current value is <jsp:getProperty name="counter" property="value"/> </body></html>

  36. Variation in scope • request • make bean accessible via the request variable • request is shared in “forward” or “include” JSP • example <jsp:useBean id=“counter" class=“jspexamples.Counter" scope=“request”/>

  37. Variation in scope • <jsp:useBean …> action • will find existing bean within scope • other scopes • session • application • available to all servlets within the same ServletContext

  38. Jsp example (1/2) <html><head> <title>Bean JSP example</title> </head><body> <jsp:useBean id="counter" class="jspexamples.Counter” scope="request"/> <jsp:setProperty name="counter“ property="value" value="10"/> <jsp:forward page="BeanTest2.jsp"/> </body></html>

  39. Jsp example (2/2): BeanTest2.jsp <html><head> <title>Bean JSP example</title> </head><body> <jsp:useBean id="counter" class="jspexamples.Counter“ scope="request"/> Value is now: <jsp:getProperty name="counter" property="value"/> </body></html>

  40. Advanced Exercise • create Shopping cart bean • share with session scope

  41. ShoppingCart bean package mypackage; import java.util.*; public class ShoppingCart { private Vector<String> products = new Vector<String>(); public String getTable() { StringBuffer buf = new StringBuffer(); Enumeration all = products.elements(); while (all.hasMoreElements()) buf.append("<TR><TD>" + all.nextElement() + "</TD>"); return buf.toString(); } public void setAddOns(String[] addOns) { for (int i = 0; i < addOns.length; i++) products.addElement(addOns[i]); } }

  42. MiniBeans.jsp <HTML><BODY> <H2>Thank you for your selection</H2> <jsp:useBean id="cart" class=“mypackage.ShoppingCart" scope="session"/> <jsp:setProperty name="cart" property="addOns" param="products"/> <TABLE><TR><TH>Content of Shopping Cart:</TH></TR> <jsp:getProperty name="cart" property="Table"/> </TR></TABLE> <jsp:include page="continue.html" /> </BODY></HTML>

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