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Server-Side Development Basics. Harry R. Erwin, PhD University of Sunderland CIT304/CSE301. Resources. Hans Bergsten, 2002, JavaServer Pages, 2nd edition, O’Reilly, ISBN: 0-596-00317-X http://java.sun.com/products/jsp/ http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/

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server side development basics

Server-Side Development Basics

Harry R. Erwin, PhD

University of Sunderland

CIT304/CSE301

resources
Resources
  • Hans Bergsten, 2002, JavaServer Pages, 2nd edition, O’Reilly, ISBN: 0-596-00317-X
  • http://java.sun.com/products/jsp/
  • http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
  • Farley, et al., 2002, Java Enterprise in a Nutshell, 2nd edition, O’Reilly, ISBN: 0-596-00152-5
  • Brittain and Darwin, 2003, Tomcat: the Definitive Guide, O’Reilly.
  • Kurniawan and Deck, 2004, How Tomcat Works, BrainySoftware.com.
  • Knuckles and Yuen, 2005, Web Applications: Concepts and Real World Design, Wiley.
  • Nakhimovsky and Myers, 2004, Google, Amazon and Beyond, Apress.
questions to be answered
Questions to be Answered
  • What is server-side programming (SSP)?
  • What are some approaches to SSP?
  • What are SSP basics?
  • What is JSP?
  • How can I support SSP?
what is server side programming ssp
What is Server-Side Programming (SSP)?
  • Technologies for developing web pages that include dynamic content—that is web applications.
  • Can produce web pages that contain information that is connection- or time-dependent.
  • A key technology for on-line shopping, employee directories, personalized and internationalized content.
history of dynamic web content
History of Dynamic Web Content
  • The Common Gateway Interface (CGI) was the first approach to providing dynamic web content. Used scripts, and a process, not just an individual thread, was dispatched for each web page generated. Hence inefficient and did not scale well.
  • Numerous second generation alternatives were invented:
    • FastCGI
    • mod_perl
    • NSAPI
    • ISAPI
    • Java Servlets
  • These embedded HTML in programming code. Hence costly in programmer time.
scripting the third generation approach
Scripting—the Third Generation Approach
  • Idea: embed simple code in HTML pages!
  • The HTML pages then use the code to choose what elements and data to display.
  • Classes and/or subroutines may be called to compute information for inclusion in the web page. Existing APIs can be invoked.
  • This is known as ‘scripting’.
some approaches to scripting
Some Approaches to Scripting
  • JavaServer Pages (JSP, uses Java sparingly, will be covered in these lectures)
  • Active Server Pages (ASP, uses VBScript, Jscript, COM or ActiveX components, ODBC). ASP.NET is quite similar to JSP, using C#. Has not been very popular.
  • PHP (C-like syntax, many functions available, insecure, covered in DL versions of CIT304)
  • ColdFusion (CFML, proprietary)
  • Java servlet template engine (Velocity, FreeMarker)

Not much change in the last five years, other than the introduction of AJAX (JavaScript + XML).

some jsp basics
Some JSP Basics
  • The HTTP protocol.
  • Servlets
the http protocol
The HTTP Protocol
  • A communications model:
    • A client, often but not always a web browser, sends a request for a resource to a server.
    • The server returns a response or an error message.
  • Points to remember:
    • Stateless protocol.
    • Delayed feedback.
    • Server cannot tell how the request was made. No client-side processing can be invoked. (If it could be, it would be a security nightmare.)
examples of http clients
Examples of HTTP Clients
  • Web browsers (many, including specialized ones for console interfaces—lynx—and handicapped users)
  • Search utilities (Sherlock on MacOS X)
  • Help utilities
  • FTP clients (e.g., interarchy on MacOS X)
  • Software registration programs
  • telnet (a hacker can emulate a web browser by connecting to port 80)
  • Specialized programs (e.g., curl)
  • Cracker toolkits (to generate malformed http requests)
http requests
HTTP Requests
  • Information is specified by an HTTP Uniform Resource Locator (URL, see RFC-2396 and RFC-2616).

http://osiris.sunderland.ac.uk:80/~cs0her/index.html

  • Consists of:
    • Protocol designation (http and https)
    • Server name:port number (port number defaults to 80 for http and 8080 443 for https)
    • Name of the resource being requested. Need not be a file. Here it is: /~cs0her/index.html
http request message
HTTP Request Message
  • Consists of:
    • Request line
      • GET resource_name protocol_in_use
      • POST (provides parameters in the request body, see below)
    • Request headers
      • Host (server name)
      • User-Agent (browser type)
      • Various Accept headers describing formats and languages
    • Request body (optional)
java servlets
Java Servlets
  • Currently, Java is the predominant language for SSP. This is due to the Java Servlet API.
  • Advantages over other SSP technologies:
    • Persistent between invocations, avoiding process instantiations.
    • Portable across operating systems and servers.
    • Good security.
    • Can use the Java APIs, particularly JDBC.
    • Is integrated closely with the J2EE environment.
servlets
Servlets
  • A servlet runs in a servlet container within a Java Virtual Machine.
  • Servlet containers:
    • Apache/Jserv, which supports Servlets 2.0.
    • Mortbay.com/Jetty
    • IBM/WebSphere
    • Jakarta/Tomcat 4.0 (This is the reference implemen-tation for the Servlet 2.3 API). Available from http://jakarta.apache.org. We will discuss Tomcat in a later lecture.
servlet basics
Servlet Basics
  • The Servlet API consists of two Java packages:
    • javax.servlet
    • javax.servlet.http
  • Required for J2EE 1.3
servlet lifecycle
Servlet Lifecycle
  • A client makes a request involving a servlet running on the server.
  • The servlet is responsible for loading and executing the Java classes that generate the HTML content.
  • To the client, this looks like standard HTML processing, except faster.
  • The servlet then need not shut down. Instead, it can handle subsequent requests without restarting.
servlet methods
Servlet Methods
  • init(), to handle startup. Once init() runs, the servlet is available.
  • service() is called to process each request. Disk writes are only needed to preserve state. Arguments to service() are ServletRequest and ServletResponse objects.
  • destroy() is called to clean up resources when the server shuts down (if it ever shuts down).
core of the api
Core of the API
  • javax.servlet.Servlet interface.
  • javax.servlet.http.Servlet class, implementing the interface. Designed to work with the HTTP protocol.
  • javax.servlet.GenericServlet class, implementing the interface. This class is communication protocol agnostic. Can implement a filtering servlet to adapt output from some other source. This can provide other protocol services (e.g., ftp).
a web application
A Web Application
  • A set of resources (servlets, static content, .jsp files, class libraries) installed in a specific path, making up a directory.
  • Should be organized as a chroot jail.
  • Multiple servlets can exist concurrently. Run in a common ServletContext.
  • Be careful—the path can change from machine to machine.
supporting jsp
Supporting JSP
  • Requirements:
    • Workstation or PC with an internet connection.
    • Java 2 SDK (available from Sun, links on my COM379 handbook page)
    • JSP 1.2-enabled web server such as Apache Tomcat (Jakarta Project). This is available here at the Informatics Centre.
sounds good
Sounds Good?
  • Not really—Java servlets have to be programmed and their configuration must be managed.
  • Programmers make $50,000-$90,000 in the USA, and programs are notoriously hard to develop and maintain. This is particularly a problem when changes to business logic force changes.
  • Next lecture: we will look at how the same thing can be done more quickly, easily, and flexibly with web pages.
conclusions
Conclusions
  • You’ve gained a general understanding of what Server Side Processing (SSP) is.
  • You’ve seen the role of SSP in HTTP processing.
  • You’ve been introduced to Java Servlets, and
  • You now know the basic configuration for servlet processing.
  • Next lecture, you will see how JavaServer Pages (JSP) interact with this environment.