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Part 4

Part 4. Web technologies: HTTP, CGI, PHP,Java applets). Types of Web Pages. Static Stored in file Unchanging Dynamic Formed by server Created on demand Output from a program Use Common Gateway Interface (CGI) technology. Types of Web Pages (cont). Active Executed at client

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Part 4

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  1. Part 4 Web technologies: HTTP, CGI, PHP,Java applets) CSI 4118 – UNIVERSITY OF OTTAWA

  2. Types of Web Pages • Static • Stored in file • Unchanging • Dynamic • Formed by server • Created on demand • Output from a program • Use Common Gateway Interface (CGI) technology CSI 4118 – UNIVERSITY OF OTTAWA

  3. Types of Web Pages (cont) • Active • Executed at client • Consists of a computer program • Can interact with user • Use Java technology CSI 4118 – UNIVERSITY OF OTTAWA

  4. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  5. CGI Technology • URL specifies • Location of Web server • CGI program on that server • Arguments to program • Web server • Uses TCP for communication • Accepts HTTP request from client • Runs specified CGI program • Returns output to client CSI 4118 – UNIVERSITY OF OTTAWA

  6. CGI Technology (cont) • CGI program • Performs arbitrary computation • Often written in a scripting language • Produces output file when run • Starts output with header CSI 4118 – UNIVERSITY OF OTTAWA

  7. Header in CGI Output • Stops at first blank line • Identifies • Encoding used • Type of document • Format keyword: information CSI 4118 – UNIVERSITY OF OTTAWA

  8. CGI Header Examples • HTML document header Content Type: text/html • Text document header Content Type: text/plain • Redirection header Location: /over_here/item4 CSI 4118 – UNIVERSITY OF OTTAWA

  9. Example CGI Script • Generates document • Document contains three lines of text • Header • Blank line • Document creation date CSI 4118 – UNIVERSITY OF OTTAWA

  10. 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 CSI 4118 – UNIVERSITY OF OTTAWA

  11. Example Environment Variables CSI 4118 – UNIVERSITY OF OTTAWA

  12. 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) CSI 4118 – UNIVERSITY OF OTTAWA

  13. Long-Term State Information • Program lifetime • CGI program invoked by server • Program exits after generating output • To maintain persistent data • Write to file on disk • Read from file on disk CSI 4118 – UNIVERSITY OF OTTAWA

  14. Long-Term State Information • Client’s IP address in environment variable • Check if address in file • Respond to client CSI 4118 – UNIVERSITY OF OTTAWA

  15. 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 CSI 4118 – UNIVERSITY OF OTTAWA

  16. Short-Term State Information • Argument encodes number of times executed CSI 4118 – UNIVERSITY OF OTTAWA

  17. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  18. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  19. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  20. Server-Side Scripting • ASP (Active Server Pages) • JSP (Java Server Pages) • PHP (Perl Helper Pages) • ColdFusion CSI 4118 – UNIVERSITY OF OTTAWA

  21. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  22. Continuously Changing Information • Needed for • Animations • Rapid updates (e.g., stock prices) • Achieved with two mechanisms • Server push • Active document CSI 4118 – UNIVERSITY OF OTTAWA

  23. Server Push Technology • Client forms connection • Server sends updates repeatedly • Impractical CSI 4118 – UNIVERSITY OF OTTAWA

  24. Active Document Technology • Server • Sends computer program to client • Client • Runs program locally • Program • Controls display • Interacts with user CSI 4118 – UNIVERSITY OF OTTAWA

  25. Active Document Representation • Desire • Platform independence • Efficient execution • High-speed data transmission • Late binding • Consequence • Compact representation • Interpretive execution CSI 4118 – UNIVERSITY OF OTTAWA

  26. Active Document Translation • Compiler produces machine-independent binary • Browser interprets binary CSI 4118 – UNIVERSITY OF OTTAWA

  27. Java Technology • Developed by Sun Microsystems • Used for • Conventional applications • Active documents (applets) • Includes • Programming language • Run-time system • Class library CSI 4118 – UNIVERSITY OF OTTAWA

  28. Java Language Characteristics • High level • General purpose • Similar to C++ • Object oriented • Dynamic • Strongly typed • Statically type checked • Concurrent CSI 4118 – UNIVERSITY OF OTTAWA

  29. Java Run-Time Environment Characteristics • Interpretative execution • Automatic garbage collection • Multi-threaded execution • Internet access • Graphics support CSI 4118 – UNIVERSITY OF OTTAWA

  30. Java Library • Classes for • 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

  31. 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. CSI 4118 – UNIVERSITY OF OTTAWA

  32. Example Java Applet • Window with two items • Text area • Button • Change text when button clicked CSI 4118 – UNIVERSITY OF OTTAWA

  33. Illustration of Applet Display • Initial • After user clicks button CSI 4118 – UNIVERSITY OF OTTAWA

  34. Example Applet Code CSI 4118 – UNIVERSITY OF OTTAWA

  35. 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”> CSI 4118 – UNIVERSITY OF OTTAWA

  36. Java Functionality • HTML interface • Controls display • Interacts with user • HTTP interface • Accesses remote Web documents • Invokes other applets • Exceptions • Indicate unanticipated circumstances • Can be caught and handled CSI 4118 – UNIVERSITY OF OTTAWA

  37. Example Applet Code CSI 4118 – UNIVERSITY OF OTTAWA

  38. Example Applet Code (continued) CSI 4118 – UNIVERSITY OF OTTAWA

  39. Illustration of Applet Display CSI 4118 – UNIVERSITY OF OTTAWA

  40. JavaScript Technology • Alternative to Java technology • Provides scripting language • Browser reads and interprets script in source form • JavaScript can be integrated with HTML CSI 4118 – UNIVERSITY OF OTTAWA

  41. JavaScript Example CSI 4118 – UNIVERSITY OF OTTAWA

  42. JavaScript Example CSI 4118 – UNIVERSITY OF OTTAWA

  43. Summary • Web is major application in Internet • Client • Called browser • Fetches and displays document • Web documents • Stored on servers • Standard representation is HTML CSI 4118 – UNIVERSITY OF OTTAWA

  44. Summary (continued) • HTML • Markup language • Uses tags embedded in text • URL components • Protocol • Domain name of server • Protocol port number • Path of item • Only domain is required CSI 4118 – UNIVERSITY OF OTTAWA

  45. Summary (continued) • Static web page • Unchanging • Dynamic web page • Output from a program on the server • Active web page • Runs in browser • Consists of a computer program CSI 4118 – UNIVERSITY OF OTTAWA

  46. Summary (continued) • Dynamic web page technology • Known as CGI • CGI program usually a script • Document begins with header line • URL can contain arguments CSI 4118 – UNIVERSITY OF OTTAWA

  47. Summary (continued) • Active web page technology • Known as Java • Programming language plus runtime support • Document called applet CSI 4118 – UNIVERSITY OF OTTAWA

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