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CS6320 – JSP

CS6320 – JSP. L. Grewe. Java Server Pages. Servlets require you to write out entire page delivered with print statements JSP embedded in static html content File extension .jsp Not compiled

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CS6320 – JSP

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  1. CS6320 – JSP L. Grewe

  2. Java Server Pages • Servlets require you to write out entire page delivered with print statements • JSP embedded in static html content • File extension .jsp • Not compiled • Deploy as part of webapp but, location of jsp files variable (see deployment and your server information) • Language of tags, can use Java • JSP run as servlets when envoked • Invokes special _jspService() method …do not have the doGet (do*) methods.

  3. How it works. JSP engine on server receives request for a .jsp page it: • Reads in the page, and transforms the contents to a Servlet • Even the static HTML is converted to print statements, printing to the output stream associated with the JSP’s _jspService() method. • This translation is done the first time the page is requested. • Then the server runs the resulting created Servlet and returns the results to the client.

  4. Elements of a Java Server Page • Expressions: <%= %> • expression is evaluated and inserted into Servlet’s output. • Scriptlets: <% %> • This code is directly inserted into the produced Servlet’s _jspService() method. • This method is automatically called by the Servlet’s service() method. • Comments: <%-- --%> • User readable comments, not parsed by the JSP Compiler • Difference between this an HTML comment is this is inserted into the Servlet being produced by evaluating the .jsp file.

  5. Elements of a Java Server Page • Directives: <%@ %> • Provide global information to the page • Import statements • Scripting language • Declarations: <%! %> • For page-wide variable and method declaration • The code is inserted into the body of the produced Servlet, outside of any existing method (like _jspService())

  6. 2 forms of tags <%= your_expression %> OR the XML compliant version <jsp:expression> your_expression </jsp:expression>

  7. JSP Expression Example <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>HelloWorld</title> </head> <body> <p> The time is now <%= new Date() %>. </body> </html>

  8. JSP Scriptlets • JSP scriptlets are defined as block of Java code embedded between a pair of • tags, <% and %>. • Example: <% java.util.Date d = new java.util.Date(); out.println(d); %>

  9. JSP Directives • General syntax: • <%@ directive {attribute = "value"} %> • Possible values for directives are: • Page - Information for the page • Include - Specifies the files whose contents are to be included in the output • e.g., <%@ include file="header.html" %> • Taglib • The URI for a library of custom tags that may be used in the page

  10. Directive Examples <%@ page language="java“ import =“java.util.*” %> • Imports classes <%@ include file="relative-URL" %> • Includes files <jsp:forward page="next.jsp">    Zero or more <jsp:param name="x" value="y"> tags </jsp:forward> • Forwards with parameters to another resource See JSP documentation for more

  11. Directive Examples (Contd.) <%@ page session = "true | false" %> • true indicates that session data is available to the page • By default, this is set to true <%@ page buffer = "none | 16kb | sizekb" %> • Determines the size of the output stream buffer • Defaults to 8kb • Use with autoFlush <%@ page autoFlush = "true | false" %> • When set to true, flushes the output buffer when it is full, rather than raising an exception

  12. JSP Declarations • Class and instance variables (of the generated servlet class) may be specified using the JSP Declaration tag: <%! String name = “Web Applications"; int index = 10; int count = 0; %> • Methods may also be specified: <%! private int getNextIndex() {return index ++;} %>

  13. JSP PreDefined Objects • When writing scriptlets and expressions, the following objects (called implicit objects) are available by default: • request javax.servlet.http.HttpServletRequest • response javax.servlet.http.HttpServletResponse • out javax.servlet.jsp.JspWriter • session javax.servlet.http.HttpSession • application javax.servlet.ServletContext • exception java.lang.Throwable

  14. JSP Session Example <html><head><title> Visitor Count -- JSP Session </title> </head> <body bgcolor="#FFFFFF"> <font face="Helvetica"> <h2> Visitor Count </h2> <p> This JSP page demonstrates session management by incrementing a counter each time a user accesses a page. <p> <%! private int totalHits = 0; %>

  15. JSP Session Example <% session = request.getSession(true); Integer ival = (Integer)session.getValue("jspsession.counter"); if (ival == null) { ival = new Integer(1);} else {ival = new Integer(ival.intValue() + 1);} session.putValue("jspsession.counter", ival); %>

  16. JSP Session Example <center> <font size=+2> You have hit this page <%= ival %> time<%= (ival.intValue() == 1) ? "" : "s" %>, out of a total of <%= ++totalHits %> page hit<%= (totalHits == 1) ? "" : "s" %>! </font> </center> <p> </font> </body> </html>

  17. More….. • SEE the course website, and the current JSP api for more details.

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