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DT211/3 Internet Application Development

DT211/3 Internet Application Development. Introduction to Java Server Pages (JSP). Introduction . First – need to know the various “java” related terms: J2EE, J2SE, JDK, JRE, JSP,JSTL, Java Servlets,Tomcat, Apache etc…. Introduction – J2EE.

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DT211/3 Internet Application Development

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  1. DT211/3 Internet Application Development Introduction to Java Server Pages (JSP)

  2. Introduction • First – need to know the various “java” related terms: J2EE, J2SE, JDK, JRE, JSP,JSTL, Java Servlets,Tomcat, Apache etc…..

  3. Introduction – J2EE • Sun Microsystems supply the Java 2 Enterprise Edition(J2EE) platform, enabling developers to develop java based enterprise applications • J2EE is a standard set of technologies and APIs • (note: J2SE is the standard edition of the java platform but is not geared at large enterprise environments with distributed systems) • J2EE includes the following components: Java Server Pages Java beans Servlets Java Messaging JNDI JDBC

  4. Introduction – J2EE • Since J2EE is a specification, vendors create productsthat support the J2EE specifcation e.g. Apache, IBMWebSphere, BEA Weblogic. • From a web perspective, the J2EE applications that areparticularly relevant are: • Java Server PagesJava servletsJava Beans Can be used on its ownor with beans/servlets to create a webapplication Can be used on its ownor with JSP/beans to create a webapplication More complex web applications may use all 3

  5. Introduction – JDK • The (JDK) Java Development Kit is the collective name for the various development components supplied in the J2EE (or J2SE). • The Java Runtime Environment (JRE) is consists of the components required to run a java application

  6. Introduction to JSP • Java Server Pages – A technology for developing web • pages that include dynamic content • Created by SUN microsystems • ‘Equivalent’ of Microsoft’s Active Server Pages technology • Pages have a file extension of .JSP • JSPs enable web developers to enhance HTML code • by adding special JSP elements that are processed by the • server • Will use JSP v2.0

  7. Advantages of JSP • JSP pages are pre-compiled  Fast • Part of the Sun’s J2EE - Can be used with other types of java technologies, such as servlets - flexible • JSP is a specification  multiple vendors support it  commercially stable/not ‘fly by night’ technology • Easy to develop: HTML can be easily maintained with JSP. Relatively minimal programming skills required. • JSP page code is not visible on client – only generated HTML is visible

  8. Running JSP pages Not automatically included with all web servers • To develop and run JSP pages, need: • - Java Developer Kit (JDK which is part of J2EE) or higher AND a Web server that contains a JSP Container • JSP Containers are not automatically included with all Web servers • Examples of web servers that contain a JSP container are Apache Tomcat and Blazix.

  9. JSP Containers • JSP Container • The JSP Container intercepts all client request for JSP pages • First time a JSP page is requested, the Container converts the page into a java program called a Servlet and compiles -- Translation phase • For all follow-on request, the Container processes each request by invoking the appropriate servlet and then generating the response - Request processing phase • Q: What happens if the JSP page is changed?

  10. How a JSP page is processed by server First time through, JSP is translated to a servlet After, container goes directly to the servlet in the request processing phase If JSP page is changed, servlet is re-compiled

  11. JSP and Apache • Apache project have a sub project called Jakarta(see http://jakarta.apache.org/index2.html) • Jakarta project produces • Tomcat web server (nicknamed Catalina) • Tomcat webserver incorporates JSP container (nicknamed Jasper)

  12. Software Versions JSP technology developing rapidly  New version contain major new capabilities  Always note the JSP container version you are working with, and check functionality supported (on apache website) This course using Apache Tomcat Version 5 JSP 2 JSLT 1.1 Servlet 2.4

  13. To run a JSP Using apache Tomcat… Create your web application directory Create the subset WEB-INF directory (won’t run without this) Put JSP page into web application directory Call from the browser http://localhost:8080/webapp/somename.jsp

  14. To run a JSP In the background – Tomcat will retrieve the JSP page from the web server If it’s the first time JSP page has been called/run or if page has changed, Tomcat will compile the JSP page (into a servlet) - .java and .class placed in /work directory. - subsequent calls to page will be faster as no compile needed JSP page will be presented back to the user

  15. Simplest JSP.. Helloworld • Prints out message to user when JSP is loaded.. • Tomcat demo..

  16. Another Simple JSP example <html> <%@ page import="java.util.Date" %> <head> <title>JSP DATE EXAMPLE</title> </head> <body bgcolor=#ffffff> <h1>JSP DATE</h1> <h2> The current date is <%= new Date() %>. </h2> </body> </html> Prints out the current date

  17. Readability of JSP pages • Always always always ensure that code is: • INDENTED COMMENTED CONTAINS AN ID BLOCK • Indented - to reflect level of the code <html> • <head>ajsdlkfjads etc • 2) Well commented. Comments in JSP appear as<%-- calculate the sum of x and z here --%> • Comments in HTML appear as <!--- this is a comment --> • HTML comments will be visible by view source in browser, JSP comments won’t.

  18. Readability of JSP pages 3) Titled with an ID block: At the top of each JSP page, should have an ID block explaining who write the script, date, script name, description and any revisions. Can use either JSP or HTML comments (depending on whether users should be able to see the ID block) <%-- ********************************************* *** Script name: addition.jsp *** *** Author: Keith Morneau *** *** Date: July 7th 2006 *** *** Desciption: whatever it does.. *** *** Revisions: *** *** August 8th 2006: added subroutine *** ************************************************ --%> etc

  19. JSP techniques JSP provides variety of techniques to enable dynamic processing: • Directive elements In this topic • Scripting elements (java) • Action elements and Java Standard Tags Library • Java Beans

  20. JSP Pages: Directive Elements • Directive Elements - Used to provide information about the general set-up of the page. e.g. inclusion of header files, name of page to report errors, whether session tracking is required etc • Always enclosed between <%@ …… %> • Syntax: <%@ directivename attribute = “value”, attribute = “value” …. %>

  21. JSP Pages: Directive Elements • There are Three directives available to use: • <%@ page ….. > • <%@ include …… %> • <%@ taglib ….. %>

  22. Directive Elements • Each directive has a set of associated attributes (similar to some tags in HTML) • Usually placed at top of JSP file but doesn’t have to be • Example: • <%@ page import="java.util.*, java.lang.*" %> • Full list of attributes available at: http://java.sun.com/products/jsp/syntax/1.1/syntaxref11.html

  23. Directive Elements: Page Page directive - defines attributes that apply to an entire JSP page. Examples <%@page contentType = “text/html” %> <%@page language = “java” %> <%@ page errorPage="error.jsp" %>

  24. Directive Elements: Page List of attributes includes <%@ page [ language="java" ][ import="{package.class | package.*}, ..." ][ session="true|false" ][ isThreadSafe="true|false" ] *multiple threads allowed or not[ info="text" ] *gives info about the page to administration[ errorPage="relativeURL" ][ contentType="mimeType [ ;charset=characterSet ]" | "text/html ; charset=ISO-8859-1" ][ isErrorPage="true|false" ] *Specifies whether exception object available or not%>

  25. Directive Elements: Include Include directive - Includes a static file in a JSP file attranslation time Syntax <%@ include file="relativeURL" %> The included file can be an HTML file, a JSP file, a text file, or a code file written in the Java programming language Useful for including repetitive HTML content across a web site – headers, navigation bars, footers etc Useful for common logic – e.g. date displays

  26. Directive Elements: Include Example: jsp page name = includexample.jsp <html><head><title>An Include Test</title></head><body bgcolor="white"><font color="blue">The current date and time is<%@ include file="date.jsp" %></font></body></html>

  27. Directive Elements: Include Example (continued) jsp page name = date.jsp <%@ page import="java.util.*" %><%= (new java.util.Date() ).toLocaleString() %> Included into includexample.jsp from previous page When includexample.jsp is run, displays as The current date and time areAug 30, 2006 2:38:40

  28. Directive Elements: Taglib Taglib directive - Defines a tag library and prefix for the custom tags used in the JSP page. Syntax <%@ taglib uri="URIToTagLibrary“ prefix="tagPrefix" %> Example: <%@ taglib uri=“http://java.sun.com/jstl/core“ prefix=“c" %> More on taglib directives later when we use Java Standard Tag Library (JSTL)

  29. Directive Elements: summary • Three directives: page, include, taglib • Used to define general set-up information about the JSP page • By themselves, don’t “do” anything • At least one used in most JSP pages

  30. JSP dynamic processing Done • Directive elements • Scripting elements • Action elements and JSTL • Java Beans

  31. Scripting elements Developers in JSP can insert java code directly into a JSP pages using scripting elements The code is executed when the page is requested • Should be used with extreme care: • Too much code  difficult to maintain • Difficult for HTML programmers • More suitable for simple applications with small development team Q: How do you specify that the language being used in page by scripting elements is java? A: Page directive language attribute

  32. Scripting elements • Three types of scripting elements: • Expressions: The expression syntax <%= ... %> defines a scripting language expression .. “result” • Scriptlets: The scriptlet syntax <% ... %> can handle declarations, expressions, or any other type of code fragment valid in the page scripting language. • When you write a scriptlet, end the scriptlet with %> before you switch to HTML, text, or another JSP tag • 3. Declarations: The declaration syntax <%! ... %> declares variables or methods.

  33. Scripting elements: Expressions • Expressions: • Contains any valid java expression in the JSP page • Used to output dynamic values directly onto web page (e.g. result of a calculation, dates) • Enclosed between <% and %> • output as a string • Syntax <%= expression %> e.g. <% = 1+1%>

  34. Expressions - examples • E.gs: any valid java expression <%= Math.sqrt(2) %><%= items[i] %><%= a + b + c %><%= new java.util.Date() %>

  35. Scripting elements: Expressions Example <html> <body> Current time is: <%= new java.util.Date() %> </body> </html>

  36. Scripting elements: Expressions • Note: • Evaluated at run time. Result is added to the response body and output directly to web page • Can use an expression within a line of text, whether or not it is tagged with HTML • Must be a valid java expression • No “;” required at end of expression (unlike scriptlets)

  37. Scripting elements • Three types of scripting elements: • Expressions • Scriptlets • Declarations

  38. Scripting elements: Scriptlets • Scriplets are java code fragments with a JSP page • Enables more complex functionality than expressions • Java code is placed between <% and %> characters (just like expressions, but without the = sign at the start of the sequence.) • Can have any number of valid java code statements • Scriptlet contains Java code that is executed every time the JSP is invoked • Syntax: <% code %>

  39. Scripting elements: Scriptlets Example – jsp page that outputs numbers 1 to 10 onto a web page html> <head> <title>Count to 10 in JSP scriptlet</title> </head> <body> <% for(int i=1;i<=10;i++) {%> <%=i%><br/> <% } %> </body> </html> Scriptlets Expression used to output to page. Can’t put HTML Tags into the scriptlet. Can onlycontain valid java code

  40. Scripting elements: Scriptlets Example – jsp page that outputs numbers 1 to 10 onto a web page – Output in browser will be:.. Count to 10 in JSP 1 2 3 4 5 6 7 8 9 10

  41. Scriplets: mixing scriplets with HTML and other tags • When you mingle scripting elements with HTML and JSP tags, you must always end a scripting element before you start using tags and then reopen the scripting element afterwards, like this: <% } else { %> <!-- closing the scriptlet before the tags start -->... tags follow ...<% } %> <!-- reopening the scriptlet to close the language block --> At first, this may look a bit strange, but it ensures that the scripting elements are transformed correctly when the JSP source file is compiled

  42. Scripting elements: Scriptlets Example 2 –jsp page that outputs “Hello! The time is now Wed Sep 03 13:17:58 BST 2006 Your machine's address is 127.0.0.1” onto a web page <HTML> <BODY> <% java.util.Date date = new java.util.Date(); %> Hello! The time is now <% out.println( date ); out.println( "<BR>Your machine's address is " ); out.println( request.getRemoteHost()); %> </BODY> </HTML> Note: could have put this line outside the scriptlet as HTML

  43. Scripting elements: Scriptlets Note: Any text, HTML tags, or JSP elements you write must be outside the scriptlet Readability: Mixture of Tags and Java code can be difficult to read – especially for HTML developers

  44. Scripting elements: Scriptlets <% if (Math.random() < 0.5) { %> Have a <B>nice</B> day! <% } else { %> Have a <B>lousy</B> day! <% } %> In background, JSP container compiles the JSP page into Java code.. converting the HTML snippets into java code to out.print statements ---

  45. Scripting elements: Scriptlets JSP code on previous page will be converted in background to the following java code.. if (Math.random() < 0.5) { out.println("Have a <B>nice</B> day!"); } else { out.println("Have a <B>lousy</B> day!"); }

  46. Scripting elements: Scriptlets Example 3 – fragment of JSP page that generates a table in HTML containing numbers 1 to n <TABLE BORDER=2> <% for ( int i = 0; i < n; i++ ) { %> <TR> <TD>Number</TD> <TD><%= i+1 %></TD> </TR> <% } %> </TABLE> HTML within “for” loop is output n times Note: would need to supply int variable n before it will work…

  47. Scripting elements • Three types of scripting elements: • Expressions • Scriptlets • Declarations

  48. Scripting elements: Declarations Declaration: Declares a variable or method that can be used throughout the JSP page Examples <%! int i = 0; %><%! int a, b, c; %><%! Circle a = new Circle(2.0); %> Syntax <%! declarations; %> Note the “ ;”

  49. Scripting elements: Declarations Declarations don’t generate any output onto the page by themselves - usually used with expressions and/or scriptlets Examples <%! private int accessCount; %> Accesses to page since server reboot: <%= ++accessCount %> Prints the number of times the current page has been requested since the server was booted

  50. Scripting elements: Declarations Example – Declares method getDate() <%@ page import="java.util.*" %> <HTML> <BODY> <%! Date theDate = new Date(); Date getDate() { System.out.println( "In getDate() method" ); return theDate; } %> Hello! The time is now <%= getDate() %> </BODY> </HTML> Method getDate() returns a Date object

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