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Part 4 Web technologies: HTTP, CGI, PHP,Java applets) FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 1 Types of Web Pages Static Stored in file Unchanging Dynamic FALL 2005 Formed by server Created on demand Output from a program Use Common Gateway Interface (CGI) technology CSI 4118 – UNIVERSITY OF OTTAWA 2 Types of Web Pages (cont) Active FALL 2005 Executed at client Consists of a computer program Can interact with user Use Java technology CSI 4118 – UNIVERSITY OF OTTAWA 3 Summary of Web Document Types Web documents can be grouped into three categories depending on when the information in the document changes. The information in a static document remains unchanged until the author revises the document. The information in a dynamic document can change whenever a server receives a request for the document. Information displayed by an active document can change after the document has been loaded into a browser. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 4 CGI Technology URL specifies Location of Web server CGI program on that server Arguments to program Web server FALL 2005 Uses TCP for communication Accepts HTTP request from client Runs specified CGI program Returns output to client CSI 4118 – UNIVERSITY OF OTTAWA 5 CGI Technology (cont) CGI program FALL 2005 Performs arbitrary computation Often written in a scripting language Produces output file when run Starts output with header CSI 4118 – UNIVERSITY OF OTTAWA 6 Header in CGI Output Stops at first blank line Identifies Encoding used Type of document Format keyword: information FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 7 CGI Header Examples HTML document header Content Type: text/html Text document header Content Type: text/plain Redirection header Location: /over_here/item4 FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 8 Example CGI Script Generates document Document contains three lines of text FALL 2005 Header Blank line Document creation date CSI 4118 – UNIVERSITY OF OTTAWA 9 Parameters CGI programs can be parameterized URL can contain arguments that are passed to CGI program Question mark separates CGI path from arguments Server places information following question mark in environment variable QUERY_STRING FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 10 Example Environment Variables FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 11 Encoding Information in a URL Information that program stores between invocations: state information Information passed to browser in form of cookie Cookie consists of name/value pair Long term (persistent) or short term (session) FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 12 Long-Term State Information Program lifetime CGI program invoked by server Program exits after generating output To maintain persistent data FALL 2005 Write to file on disk Read from file on disk CSI 4118 – UNIVERSITY OF OTTAWA 13 Long-Term State Information Client’s IP address in environment variable Check if address in file Respond to client FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 14 Short-Term State Information Each invocation of a dynamic document program can produce a document containing a new set of URLs Use new arguments in new URLs FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 15 Short-Term State Information Argument encodes number of times executed FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 16 Example of Script Execution Initial document Content-type: text/html <HTML> This is the initial page.<BR><BR> <A HREF=“http://www.nonexist.com/cgi/ex4?1”> Click here to refresh the page.</A> </HTML> Resulting display This is the initial page. Click here to refresh the page. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 17 Example of Script Execution Generated output Content-type: text/html <HTML> You have displayed this page 2 times.<BR><BR> <A HREF=“http://www.nonexist.com/cgi/ex4?2”> Click here to refresh the page.</A> </HTML> Resulting display You have displayed this page 2 times. Click here to refresh the page. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 18 Generated URL Values When it generates a document, a dynamic document program can embed state information as arguments in URLs. The argument string is passed to the program for the URL, enabling a program to pass state information from one invocation to the next. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 19 Server-Side Scripting ASP (Active Server Pages) JSP (Java Server Pages) PHP (Perl Helper Pages) ColdFusion FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 20 Server-Side Scripting Server-side scripting technologies allow a dynamic page to be created from a template or skeleton that contains embedded commands or program scripts. Instead of using a computer program to generate an entire page, an interpreter copies the page and replaces only the scripting commands. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 21 Continuously Changing Information Needed for Animations Rapid updates (e.g., stock prices) Achieved with two mechanisms FALL 2005 Server push Active document CSI 4118 – UNIVERSITY OF OTTAWA 22 Server Push Technology Client forms connection Server sends updates repeatedly Impractical FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 23 Active Document Technology Server Client Sends computer program to client Runs program locally Program FALL 2005 Controls display Interacts with user CSI 4118 – UNIVERSITY OF OTTAWA 24 Active Document Representation Desire Platform independence Efficient execution High-speed data transmission Late binding Consequence FALL 2005 Compact representation Interpretive execution CSI 4118 – UNIVERSITY OF OTTAWA 25 Active Document Translation Compiler produces machine-independent binary Browser interprets binary FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 26 Java Technology Developed by Sun Microsystems Used for Conventional applications Active documents (applets) Includes FALL 2005 Programming language Run-time system Class library CSI 4118 – UNIVERSITY OF OTTAWA 27 Java Language Characteristics High level General purpose Similar to C++ Object oriented Dynamic Strongly typed Statically type checked Concurrent FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 28 Java Run-Time Environment Characteristics Interpretative execution Automatic garbage collection Multi-threaded execution Internet access Graphics support FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 29 Java Library Classes for FALL 2005 Graphics manipulation Low-level network I/O Interaction with a Web server Run-time system access File I/O Conventional data structures Event capture Exception handling CSI 4118 – UNIVERSITY OF OTTAWA 30 Choice of Graphics Interface Java includes an extensive graphics toolkit that consists of run-time support for graphics as well as interface software. The toolkit allows a programmer to choose a high-level interface, in which the toolkit handles details, or a low-level interface, in which the applet handles details. FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 31 Example Java Applet Window with two items Text area Button Change text when button clicked FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 32 Illustration of Applet Display Initial After user clicks button FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 33 Example Applet Code FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 34 Applet Invocation Available in HTML Uses applet tag Specifies Codebase (machine and path) Code (specific class to run) Example <applet codebase=“www.nonexist.com/pth” code=“bbb.class”> FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 35 Java Functionality HTML interface HTTP interface Controls display Interacts with user Accesses remote Web documents Invokes other applets Exceptions FALL 2005 Indicate unanticipated circumstances Can be caught and handled CSI 4118 – UNIVERSITY OF OTTAWA 36 Example Applet Code FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 37 Example Applet Code (continued) FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 38 Illustration of Applet Display FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 39 JavaScript Technology Alternative to Java technology Provides scripting language Browser reads and interprets script in source form JavaScript can be integrated with HTML FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 40 JavaScript Example FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 41 JavaScript Example FALL 2005 CSI 4118 – UNIVERSITY OF OTTAWA 42 Summary Web is major application in Internet Client Called browser Fetches and displays document Web documents FALL 2005 Stored on servers Standard representation is HTML CSI 4118 – UNIVERSITY OF OTTAWA 43 Summary (continued) HTML Markup language Uses tags embedded in text URL components FALL 2005 Protocol Domain name of server Protocol port number Path of item Only domain is required CSI 4118 – UNIVERSITY OF OTTAWA 44 Summary (continued) Static web page Dynamic web page Unchanging Output from a program on the server Active web page FALL 2005 Runs in browser Consists of a computer program CSI 4118 – UNIVERSITY OF OTTAWA 45 Summary (continued) Dynamic web page technology FALL 2005 Known as CGI CGI program usually a script Document begins with header line URL can contain arguments CSI 4118 – UNIVERSITY OF OTTAWA 46 Summary (continued) Active web page technology FALL 2005 Known as Java Programming language plus runtime support Document called applet CSI 4118 – UNIVERSITY OF OTTAWA 47
