Server side development basics
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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.


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