Web programming for project students

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Web programmingfor project students

• Dr Jim Briggs

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What is the web?

• Distributed system
• Client-server system
• Characteristics of clients and servers
• Servers always on / Clients choose when on
• Clients do not need high performance if the work
  is done on the server
• Protocol based

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Basic architecture of the web
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Common web tools

• Browsers
• Microsoft Internet Explorer
• Netscape Navigator
• Mozilla (Firefox)
• Opera
• Safari
• Konqueror
• Lynx

• Servers
• Apache
• Internet Information Server (Microsoft)
• Sun
• Netscape
• Omni
• Roxen
• NCSA

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HTTP protocol

• Specified by
• http//www.w3.org/Protocols/rfc2616/rfc2616.html
• Based on requests and responses
• A response can contain any document
• MIME (Multipurpose Internet Mail Extensions)
  types
• http//www.iana.org/assignments/media-types/
• A stateless protocol
• Normally transported via a TCP/IP connection
• Default port is TCP 80

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HTTP requests

• Requests
• GET
• POST
• PUT
• HEAD
• Example request
• GET http//www.port.ac.uk/index.htm HTTP/1.1

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HTTP responses

• HTTP/1.1 200 OK
• Server Microsoft-IIS/4.0
• Date Mon, 29 Apr 2002 085053 GMT
• Content-Type text/html
• Accept-Ranges bytes
• Last-Modified Wed, 10 Apr 2002 161234 GMT
• ETag "085fb85aae0c1154fb"
• Content-Length 13845
• ltHTMLgt
• ltHEADgt
• ltTITLEgtUniversity of Portsmouth - Our
  Universitylt/TITLEgt
• ...

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An error response

• HTTP/1.1 404 Object Not Found
• Server Microsoft-IIS/4.0
• Date Mon, 29 Apr 2002 085812 GMT
• Content-Length 11891
• Content-Type text/html
• ltHTMLgt
• ltHEADgt
• ltTITLEgtUniversity of Portsmouth - Our
  Universitylt/TITLEgt
• ...

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Dynamic web pages

• Four models
• Server-side includes
• CGI
• Server modules
• Auxiliary servers

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CGI architecture
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CGI specification

• Specified at http//hoohoo.ncsa.uiuc.edu/cgi/

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Server module
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Auxiliary server
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Common web languages

• Java/JSP
• ASP (.NET) / C
• PHP
• Perl
• Ruby on Rails

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Architecture of aJava web application
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Introduction to Java web apps

• Servlets and JSPs
• Servlet container
• Tomcat
• A container may run several (independent) web
  applications (webapps)
• Each must have a WEB-INF directory
• web.xml configuration file
• classes directory
• lib directory

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Important classes and interfaces 1

• All servlets must implement the Servlet interface
• Class HttpServlet
• init/destroy
• doGet/doPut
• Your servlet will derive from this

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Important classes and interfaces 2

• 2 parameters to a request handling method
• Class HttpServletRequest
• String param request.getParameter(name)
• Class HttpServletResponse
• PrintWriter out response.getWriter()
• Class HttpSession
• Holds data common to related requests

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JavaServer Pages (JSP)

• Distinction
• servlets HTML embedded in program
• JSP program embedded in HTML
• Useful where majority of effort is page design
• Translated automatically into a servlet
• Retranslated if changed (no need to restart
  server)
• Can be placed anywhere in a web application
• but not visible to client if in the WEB-INF
  directory

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JSP elements

• Scriptlets
• Actions
• Directives
• Standard tags
• Custom tags
• Expression language

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Scriptlets

• Any Java code between lt gt
• Expressions
• lt name gt
• Declarations
• lt! String name gt
• DEPRECATED
• Do not use - not XML
• Much easier to use JSTL

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JSP actions

• Including other files
• ltjspinclude page"path"/gt
• Request time inclusion
• Accessing beans
• ltjspusebean id"beanName" class"package.class"
  scope"session"/gt
• ltjspgetproperty name"beanName"
  property"propertyName"/gt
• ltjspsetproperty name"beanName"
  property"propertyName" value"newValue"/gt

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JSP directives

• Page directive
• lt_at_page import"package.class"gt
• lt_at_page contentType"text/html"gt
• lt_at_page errorPage"URL"gt
• Include directive
• lt_at_include file"filename"gt
• Translation time inclusion

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Java Standard Tag Library (JSTL)

• Taglib directive
• lt_at_ taglib prefix"c" uri"http//java.sun.com/jst
  l/core" gt
• Core
• ltcout value"anExpression"/gt
• SQL
• XML
• Format

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Custom tags

• Implement your own tags
• Create a Tag Library Definition (tld) file
• Extend predefined classes
• Specify your library in a _at_taglib directive
• Use like JSTL tags

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Expression language

• Refer to Java Beans and other common classes
• expression can appear as tag attributes or
  (since JSP 2.0) in the page itself
• Several implicit objects
• header
• header"user-agent"
• param
• param'name'
• param.name

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Java tools

• NetBeans
• IDE
• edit, compile, build, run, debug
• lots of wizards
• support for Struts
• support for Hibernate (through nbxdoclet)
• Eclipse

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Web applicationsystem architecture
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Model View Controller (MVC)
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MVC in Java
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Relationship betweenStruts and Hibernate
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Struts information flow
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Role of the persistence layer