CS6320 JSP L Grewe 1 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 2 How it works JSP engine on server receives request for a jsp page it 1 2 3 4 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 3 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 4 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 5 2 forms of tags your expression OR the XML compliant version jsp expression your expression jsp expression 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 More SEE the course website and the current JSP api for more details 17