CGI : Java Glossary

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CGI
CGI (Computer Graphics Imaging). A non-Java technique of sending data from HTML (Hypertext Markup Language) forms in browsers to server programs written in C, Python, Tcl or Perl. They typically do data base searches or process the data in HTML forms and send back MIME (Multipurpose Internet Mail Extensions). Java can simulate the form on the client side, or replace the C with servlets on the server side. There are hundreds of tutorials, but focus on using Perl write server code with no real understanding of how it all works.
book cover recommend book⇒Core Servlets and Javaserver Pages: Advanced Technologies, Vol. 2, second editionto book home
by Marty Hall, Larry Brown, Yaakov Chaikin 978-0-13-148260-9 paperback
publisher Prentice Hall 978-0-13-271568-3 eBook
published 2007-12-01 B004YWAZFA kindle
Complete text of the book available on line in pdf format.
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book cover recommend book⇒Essential RenderMan, second editionto book home
by Ian Stephenson 978-1-84628-344-4 paperback
publisher Springer 978-1-84628-800-5 eBook
published 2007-06-26
RenderMan is the C-based tool that Pixar uses for rendering animations and special effects. Oddly B&N charges more for the eBook than for the paperback.
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German flag amazon.de Chapters Indigo Canadian flag
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book cover recommend book⇒More Servlets and Java Server Pagesto book home
by Marty Hall 978-0-13-067614-6 paperback
publisher Pearson Education
published 2001-12-26
Complete text of the book available on line in pdf format.
Australian flag abe books anz abe books.ca Canadian flag
German flag abe books.de amazon.ca Canadian flag
German flag amazon.de Chapters Indigo Canadian flag
Spanish flag amazon.es Chapters Indigo eBooks Canadian flag
Spanish flag iberlibro.com abe books.com American flag
French flag abe books.fr amazon.com American flag
French flag amazon.fr Barnes & Noble American flag
Italian flag abe books.it Nook at Barnes & Noble American flag
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GET and POST are two ways to request information from a server. In GET all the request information is contained tacked onto the URL (Uniform Resource Locator) (which can thus be made part of a bookmark). In PUT it is contained in a separate trailing message. GET is idempotent, a mathematician’s word meaning gives identical results with identical input and has no side effects. Thus if you do a second identical GET, the results can be fished out of cache, without reprocessing the request. In contrast, a POST is assumed to have side effects, or to produce different results each time it is invoked. It has some lasting effect on the world, e.g. submitting a membership application. The request has to be reprocessed from scratch.

The Cyberspyder people used to make a free tool to help you understand what browsers and servers send back and forth to each other called Webbug. It lets you compose GET commands and see the results. Unfortunately, it does not let you snoop on what browsers and servers are sending to each other.

Forms

When you fill in a form and hit submit, a message sent from your browser (or program simulating a browser) to the server looks like this:
POST actionscript HTTP/1.0
Referer: http://mindprod.com/test.html
Content-type: application/x-www-form-urlencoded
Accept: */*
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0
Content-Length: 1234
date=03%2F05%2F26&date_fmt=yymmdd
You can send such a message at the low level with Socket.getOutputStream() and read the respond with Socket.getInputStream(), or more commonly at a higher level with HttpURLConnection. See the file I/O amanuensis for details.

When you use the GET protcol the parameters are tacked on the end of the URL, separated-by a ?.

Beware of using raw Sockets for get and put for long messages. Responses come in blocks with a length field on the front. You have to bypass these. They will show up as something like 2000 cr lf in the middle of your data.

POST and GET are not efficient ways for transmitting large volumes of binary data. For that you would set up a separate socket connection.

Computer Graphics Imaging

CGI refers to rendering mathematical descriptions of scenes into 2-D or 3-D pixels for images, video games, cartoons or movies. The art has become so good, that now most of the time it takes an expert eye to tell if a scene was done with CGI or with costumed extras on a set. The cost has come down so much, even Indie filmmakers can use CGI. They might use a software tool like Pixar’s Renderman to create their files, then rent time on a cloud of machines to render a scene for $0.70 USD per core per hour. Virtual cameras simulate depth of field and motion blur. You can generate displacement detail on top of the basic geometry. This simplifies the 3D vector models.

book cover recommend book⇒Core Web Programming, second editionto book home
by Marty Hall and Gary Cornell 978-0-13-089793-0 paperback
publisher Prentice Hall 978-0-613-92274-6 hardcover
published 2001-06-03
1250 pages. Also has some simple RMI examples. This is a great doorstop of a book. It has a few chapters on client-server programming in Java and a section of that is on CGI. I have looked at hundreds of Java books and found nothing that deals in depth with client side Java talking to CGI, except Marty’s book. It is really very simple and he does an excellent job of explaining it. Marty has posted all the source code examples from the book for anyone to use. These contain updates and errata fixes you don’t get on the CD-ROM that comes with the book.
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Bignose Bird has some CGI scripts in Perl you can cannibalise. It also has some tutorials that introduce you to Perl
CGI spec
cookie
echo server
File I/O Amanuensis has sample code to do CGI in the client
HTML Forms
HTTP
HTTP Client
MIME
remote file access
Renderman
screen scraping
servlet
sniffer
URLConnection
W3C

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