Transcript Document

Software Project in
Computer Networks
CNT 4104
Dr. Janusz Zalewski
Florida Gulf Coast University
1) PHP – Personal Home Page
Scripting Language
2) JavaScript
The transition from static
webpages to dynamic
webpages means moving
from plain webpages to
web applications.
In a pill, how the web works?
1) There are two entities: a client (browser)
and a server.
2) Traditionally, the client sends some
information to the server at a specific URL,
requesting a response in a form of an
HTML file.
3) The server receives the request, processes it,
and sends the HTML file back to the client.
4) The client receives the file and based on its
HTML contents renders the webpage and
displays it.
1)
2)
3)
4)
What happens when the request to the
server is for execution of a CGI application?
There are two entities: a client (browser) and a
server (with a CGI application).
The client sends a request for execution to the
server at a specific URL, requesting a response
as usual in a form of an HTML file.
The server receives the request, processes it by
running a CGI application (a script, a C/C++
program, etc.), whose result is an HTML text,
and sends the HTML text back to the client.
The client receives the response and based on its
HTML content renders & displays the webpage.
PHP helps doing the same thing as a CGI:
1) There are two entities: a client (browser) and a
server (with a PHP processor engine).
2) The client sends a request for execution to the
server at a specific URL, requesting a response
as usual in a form of an HTML file.
3) The server receives the request, passes it to the
PHP engine, which runs a corresponding script
and delivers the results as an HTML text to the
server, which in turn passes it back to the client.
4) The client receives the response and based on its
HTML content renders & displays the webpage.
PHP Hypertext Preprocessor
(Personal Home Pages)
A scripting language that offers unified
approach to designing dynamic
webpages:
- it is free (open source)
- it is fast in execution and easy to learn
- it is universally portable to multiple
platforms.
PHP code is embedded in the HTML
code. A special tag, usually “<?PHP”:
<?PHP /* PHP code goes here */ ?>
is recognized as marking the beginning
of PHP code.
• Symbols “/*” and “*/” are C-style
comments
• Symbols “?>” mark end of PHP tag
PHP is nearly a typeless language:
• data types of variables are not declared
beforehand, but determined when a
variable is assigned a value
• data type of a variable can change
when variable receives a different value
• integer, double, string, array, object,
boolean are the data types used
Variable’s name in PHP must start with
a dollar sign $, for example: $var
Expression is a valid combination of
variables and operators, for example:
$var = 13 + ++$var
Instruction (more correctly, a statement)
is any syntactically valid entity ending
with a semicolon, for example:
$var = 13 + ++$var;
PHP code can be embedded in HTML
directly, for example:
<H2>This is
<?php
echo date('l, F dS Y.');
?>
</H2>
PHP code stored in a file can be also
invoked from HTML, for example:
<FORM ACTION="welcome1.php"
method="post">
<LABEL>First Name: <INPUT
TYPE="text" name="firstname" />
</LABEL><BR />
<LABEL>Last Name: <INPUT
TYPE="text" name="lastname" />
</LABEL><BR />
<INPUT TYPE="submit"VALUE="GO" />
</FORM>
PHP file welcome1.php would include
the code to receive values from the form:
<?php
$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
echo "Welcome to my website,
$firstname $lastname!";
?>
The typical use of PHP is with a
database:
- connecting to a database
- performing queries
- processing the results of a query
- updating database entries
- logging out and exiting
1) PHP – Personal Home Page
Scripting Language
2) JavaScript
While PHP scripts allow
interaction, they execute at
the server site, which creates
network traffic, so the need
exists for running scripts on
the client (browser) site.
Thus JavaScript was created!
JavaScript has typical syntax of
high-level languages, but does
not require type declaration for
variables. Their data types are
determined automatically when a
variable is assigned value.
JavaScript allows control of:
• the content of webpages
• the browser itself, and
• the HTML forms on the page.
In a pill, how it all works in JavaScript?
JavaScript code is embedded in the HTML code:
<SCRIPT LANGUAGE="JavaScript">
...JavaScript code goes here...
</SCRIPT>
The most interesting feature of
Javascript is event handling, which
is an asychronous program control.
Normally a program executes
statements sequentially, one after
another, perhaps branching, but
still in a predetermined sequence.
This sequence may change abruptly
when a certain event occurs, which
needs immediate attention. Such
situations happen with interrupts
at the hardware level, and with JAVA
and C++ exceptions at the software
(programming language) level.
To deal with it, one needs to develop
an interrupt of exception handler.
In JavaScript, these abrupt events are
some action requests triggered by the
client.
One can program a response to such
events using event handlers, that is,
code segments that react appropriately,
depending on the kind of action desired
by the client.
Sample events handled in JavaScript:
• onClick
• onMouseOver
• onKeyDown
• onLoad
• onSelect
• onAbort
• and many others.
Handling a sample event via a form
(under the assumption that the event
handler has been defined separately):
<FORM>
<INPUT TYPE = ”button”
VALUE = ”Click here”
onClick=”alert(You
clicked on me!”
</FORM>
JavaScript does not have:
• graphics capabilities
• file I/O
• networking
• multithreading.
Final Remarks
• Microsoft’s response to the
emergence of JavaScript was
VBScript (Visual Basic
Scripting Edition)
• JavaScript can also run on
the server side, but is much less
popular, because of PHP & perl