1. MSIS 655 Advanced Business Applications Programming
Week 15
Servlets
In this chapter you will learn:
How servlets can be used to extend a Web server's functionality.
The servlet life cycle.
To execute servlets with the Apache Tomcat server.
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15.1

2. Servlet Overview and Architecture
Small portion of the content is static text or markup
Do not produce content
Perform a task on behalf of the client
JavaServer Pages
Extension of servlet technology
Most of the content is static text or markup
Small portion of the content is generated dynamically
Servlet container (servlet engine)
Server that executes a servlet
Web servers and application servers
Sun Java System Application Server
Microsoft’s Internet Information Server (IIS)
Apache HTTP Server
BEA’s WebLogic Application Server
IBM’s WebSphere Application Server
World Wide Web Consortium’s Jigsaw Web Server
Servlet Container
An application server that provides the facilities for running Java servlets. Also called a "servlet engine" and "servlet womb," examples of servlet containers are JServ and Tomcat from the Apache Jakarta Project. Today, servlet containers also support JavaServer Pages (JSPs) by converting them to servlets. For example, Tomcat supports JSPs, but its predecessor, JServ, did not. Full blown J2EE-compliant application servers generally handle servlets, JSPs and Enterprise JavaBeans (EJBs).
Apache Jakarta Project and the Tomcat Server
The Jakarta Project creates and maintains open source software for the Java platform. It operates as an umbrella project under the auspices of the Apache Software Foundation, and all of Jakarta products are released under the Apache License. Tomcat: A popular Java servlet container from the Apache Jakarta project. Tomcat uses the Jasper converter to turn JSPs into servlets for execution. Tomcat is widely used with the JBoss application server.
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3. What are Java Servlets?
Servlets are Java technology's answer to CGI programming. They are programs that run on a Web server and build Web pages. Building Web pages on the fly is useful (and commonly done) for a number of reasons:
The Web page is based on data submitted by the user.
The data changes frequently.
The Web page uses information from corporate databases or other such sources.
The Web page is based on data submitted by the user. For example the results pages from search engines are generated this way, and programs that process orders for e-commerce sites do this as well.
The data changes frequently. For example, a weather-report or news headlines page might build the page dynamically, perhaps returning a previously built page if it is still up to date.
The Web page uses information from corporate databases or other such sources. For example, you would use this for making a Web page at an on-line store that lists current prices and number of items in stock.
Java servlets are more efficient, easier to use, more powerful, more portable, and cheaper than traditional CGI and than many alternative CGI-like technologies. (More importantly, servlet developers get paid more than Perl programmers :-).
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4. Fig. 26.1 | Servlet architecture.
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5. Servlets and JavaServer Pages (JSP)
Request-response model
Packages javax.servlet
javax.servlet.http
javax.servlet.jsp
javax.servlet.tagext
Common implementation of request-response model
Web browsers and Web servers
Form the Web components of J2EE
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6. JavaServer Pages JavaServer Pages
Extension of Servlet technology
Separate the presentation from the business logic
Simplify the delivery of dynamic Web content
Reuse existing Java components
JavaBean
Custom-tag libraries
Encapsulate complex functionality
Classes and interfaces specific to JSP
Package javax.servlet.jsp
Package javax.servlet.jsp.tagext
JSP(JavaServer Page) An extension to the Java servlet technology from Sun that allows HTML to be combined with Java on the same page. The Java provides the processing, and the HTML provides the page layout that will be rendered in the Web browser.
Dynamic Web Pages in J2EE JSPs are the primary method in the J2EE platform for displaying dynamic Web pages. Special tags let Java code be included on the page as well as inserted into HTML statements without invalidating the HTML syntax. It thus lets non-Java programmers maintain HTML pages in their favorite authoring programs without interfering with the Java code on the page. With the use of standard and custom JSP tags, the Java code can be completely hidden.
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7. JavaServer Pages Overview
JSPs
Look like standard XHTML or XML
Normally include XHTML or XML markup
Known as fixed-template data
Key components
Directives
Actions
Scripting elements
Tag libraries
When server receive the first JSP request
JSP container translates a JSP into a servlet
Handle the current and future requests
Code that represents the JSP
Placed in servlet’s _jspService method
JSP errors
Translation-time errors
Occur when JSPs are translated into servlets
Request-time errors
Occur during request processing
Methods jspInit and jspDestroy
Container invokes them when initializing and terminating a JSP
Defined in JSP declarations
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8. First JSP Example Simple JSP example (Fig. 27.1) Demonstrates
Fixed-template data (XHTML markup)
Creating a Java object (java.util.Date)
Automatic conversion of JSP expression to a String
meta element to refresh Web page at specified interval
First invocation of clock.jsp
Notice the delay while:
JSP container translates the JSP into a servlet
JSP container compiles the servlet
JSP container executes the servlet
Subsequent invocations should not experience the same delay
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10. JavaServer Pages are easier to implement than servlets when the response to a client request consists primarily of markup that remains constant between requests.
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11. Scripting Components JSP scripting components
Scriptlets (delimited by <% and %>)
Comments
JSP comments (delimited by <%-- and --%>)
XHTML comments (delimited by <!-- and -->)
Java’s comments (delimited by // and /* and */)
Expressions (delimited by <%= and %>)
Declarations (delimited by <%! and %>)
Escape sequences
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