DT 228 3 Web Development Introduction to Java Server

DT 228/3 Web Development Introduction to Java Server Pages (JSP)

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

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

Introduction – J 2 EE • Since J 2 EE is a specification, vendors create products that support the J 2 EE specifcation e. g. Apache, IBM Web. Sphere, BEA Weblogic. • From a web perspective, the J 2 EE applications that are particularly relevant are: Java Server Pages Java servlets Java Beans Can be used on its own or with beans/servlets to create a web application Can be used on its own or with JSP/beans to create a web application More complex web applications may use all 3

Introduction – JDK • The (JDK) Java Development Kit is the collective name for the various development components supplied in the J 2 EE (or J 2 SE). • The Java Runtime Environment (JRE) is consists of the components required to run a java application

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 v 2. 0

Advantages of JSP • JSP pages are pre-compiled Fast • Part of the Sun’s J 2 EE - 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

Running JSP pages To develop and run JSP pages, need: Not automatically included with all web servers - Java Developer Kit (JDK which is part of J 2 EE) 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.

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?

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 recompiled

JSP and Apache • Apache project have a sub project called Jakarta (see http: //jakarta. apache. org/index 2. html) • Jakarta project produces - Tomcat web server (nicknamed Catalina) - Tomcat webserver incorporates JSP container (nicknamed Jasper)

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

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

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

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

Another Simple JSP example <html> <%@ page import="java. util. Date" %> <head> <title>JSP DATE EXAMPLE</title> </head> <body bgcolor=#ffffff> <h 1>JSP DATE</h 1> <h 2> The current date is <%= new Date() %>. </h 2> </body> </html> Prints out the current date

Readability of JSP pages Always always ensure that code is: INDENTED COMMENTED CONTAINS AN ID BLOCK 1) 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  HTML comments will be visible by view source in browser, JSP comments won’t.

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 7 th 2006 *** Desciption: whatever it does. . *** Revisions: *** August 8 th 2006: added subroutine ************************** --%> etc