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CGI |
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Servlets |
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JSP |
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What do these have in common? |
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They are all server-side technologies! |
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What is CGI |
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How does it work? |
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Environment variables |
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Processing Forms |
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GET vs. POST |
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Examples |
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Stands for “Common Gateway Interface” |
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Server-side technology |
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Can be used: |
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Process fill-out forms |
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To generate dynamic contents |
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By a web server to run external programs |
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By a web server to get/send data from databases
and other apps |
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CGI scripts can be written in any language,
including Java |
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Perl is the most popular for CGI scripting |
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To experiment, you need a web server: |
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Xitami (www.xitami.com) |
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Jakarta-Tomcat (jakarta.apache.org/tomcat) |
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Tomcat is nice for Servlets/JSP |
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If your script generates HTML then use: |
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Content-type: text/html\n\n |
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This tells the browser what content it is about
to receive |
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Other content headers include: |
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text/plain |
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image/gif |
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image/jpg |
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#!/usr/bin/perl |
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print "Content-type:text/html\n\n"; |
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print
"<html><head><title>Test
Page</title></head>\n"; |
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print "<body>\n"; print
"<h2>Hello, world!</h2>\n"; |
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print "</body></html>\n"; |
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Some of the environment variables: |
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DOCUMENT_ROOT |
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HTTP_HOST |
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HTTP_USER_AGENT |
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REMOTE_HOST |
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REQUEST_METHOD |
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QUERY_STRING |
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CONTENT_LENGTH …etc |
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#!/usr/bin/perl |
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print "Content-type:text/html\n\n"; |
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print <<EndOfHTML; |
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<html><head><title>Print
Environment</title></head> <body> |
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EndOfHTML |
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foreach $key (sort(keys %ENV)) { |
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print
"$key = $ENV{$key}<br>\n"; |
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} |
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print "</body></html>"; |
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<form action="env.cgi"
method="GET"> |
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Enter some text here: <input
type="text" name="sample_text" size=30><input
type="submit"><p> |
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</form> |
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There are two ways to send data from an HTML
form to a CGI script |
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GET |
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POST |
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These methods determine how the form data is
sent to the server |
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The input values from the form are sent as part
of the URL |
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They are saved in the QUERY_STRING environment
variable |
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If in the above example you type: |
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“hello there John” |
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The QUERY_STRING will be: |
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Sample_text=hello+there+John |
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Spaces have been replaced with + |
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This is called URL Encoding! |
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Some commonly encoded characters |
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\t (tab) %09 |
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\n (return) %0A |
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/ %2F |
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~ %7E |
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: %3A |
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; %3B |
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@ %40 |
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& %26 |
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<form action="env.cgi"
method="GET"> |
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First Name: <input type="text"
name="fname“ size=30><p> |
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Last Name: <input type="text"
name="lname" size=30><p> |
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<input type="submit">
</form> |
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If input is: Sarah Johnson |
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$ENV{‘QUERY_STRING’} would be:
fname=Sarah&lname=Johnson |
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Parsing: |
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@values = split(/&/,$ENV{'QUERY_STRING'}); |
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foreach
$i (@values) { |
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($varname,
$mydata) = split(/=/,$i); |
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print
"$varname = $mydata\n"; |
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} |
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It is possible to send values as part of a URL
(more on this in class) |
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Source: www.javacourses.com/106/marks.html |
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More sophisticated than GET |
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Data is not sent as URL-encoded (I.e. not part
of the URL) |
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When POST is used, data is sent as a separate
message (input stream) |
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Parsing: |
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read(STDIN, $buffer, $ENV{'CONTENT_LENGTH'}); |
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@pairs =
split(/&/, $buffer); |
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foreach $pair (@pairs) { |
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($name,
$value) = split(/=/, $pair); |
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$value
=~ tr/+/ /; |
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$value
=~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; |
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$FORM{$name}
= $value; |
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} |
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What is a servlet? |
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Servlets vs. CGI scripts |
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How do they work? |
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Example |
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A server-side technology |
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Designed to overcome some limitations of
existing technologies (e.g. CGI is stateless) |
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Characteristics: |
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A light-weight task that can be executed as a
thread |
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A
servlet can remain in memory (a CGI script terminates when it finished) |
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Advantages: |
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A servlet can service multiple client requests |
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Can handle multiple clients without
reloading/reinitialization |
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Servlets are written in Java |
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Can be used to: |
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Generate
dynamic contents |
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Talk to databases |
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Work with cookies |
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Session management |
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The package: javax.servlet |
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At the top level there are three interfaces: |
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ServletConfig, Servlet, Serializable |
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The servlet interface: |
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init() |
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service() |
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destroy() |
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getServiceConfig() |
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getServiceInfo() |
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It is an abstract class that implements Servlet |
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public abstract GenericServlet implements
Servlet, ServletConfig, Serializable { |
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void
init() |
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abstract void service() |
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void
destroy() |
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ServletConfig getServletConfig() |
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String
getServiceInfo() |
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void
log() |
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} |
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It is an abstract class that extends the
GenericServlet abstract class |
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It provides a convenient framework for handling
the HTTP protocol |
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These two classes (GenericServlet and
HttpServlet) ease the task of writing servlets |
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In the simplest case, you need to provide
implementation for service() |
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Servlet is loaded into memory by server: init() |
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Servlet processes client requests: service() |
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Servlet is remove by server: destroy() |
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service() is responsible for handling incoming
client requests |
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public void service(ServiceRequest request,
ServletResponse response) throws ServletException, IOException |
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Delegates HTTP requests: doGet() & doPost() |
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Use: |
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public String getParameter(String name) |
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public String[] getParameterValues(String name) |
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So if you have a parameter name “username” in a
form then to retrieve the value use: |
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String name = request.getParameter(“username”); |
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Consider the following form: |
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<form action="RequestParamExample"
method=POST> |
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First Name: <input type=text size=20
name=firstname> |
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<br> |
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Last Name: <input type=text size=20
name=lastname> |
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<br> |
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<input type=submit> |
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</form> |
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In a browser, this would look like: |
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When “Submit Query” is clicked we have the
output: |
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First Name := Qusay |
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Last Name := Mahmoud |
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The servlet: |
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public class RequestParams extends HttpServlet { |
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public
doPost(HttpServletRequest re, HttpServletResponse response) { |
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PrintWriter out = response.getWriter(); |
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out.println("<html><body><head><title>test</title></head"); |
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out.println("<body>"); |
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String firstName = req.getParameter("firstname"); |
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String lastName = req.getParameter("lastname"); |
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out.println("First Name := " + firstName +
"<br>"); |
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out.println("Last Name := " + lastName); |
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out.println("</body></html>"); |
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} } |
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It is possible to use Servlets to generate WML |
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PrintWriter out = response.getWriter(); |
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out.println("<?xml
version=\"1.0\"?>"); |
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out.println("<!DOCTYPE wml …etc"); |
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out.println("<wml>"); |
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out.println("<card
title=\"MobileDate\">"); |
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out.println(" <p
align=\"center\">"); |
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out.println("Date and Time
Service<br/>"); |
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out.println("Date is: "+ new
java.util.Date()); |
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…etc |
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Programming cookies and keeping track of
sessions is easy with Servlets….APIs provided for this |
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Explore Cookies and Session Management on your
own! |
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Something to think about: handheld devices do
not support cookies, so how do you keep track of sessions?? |
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Server-side technology |
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Enables you to embed Java code within an HTML
document |
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JSP documents have the extension .jsp |
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When an HTTP request is received, the
compilation engine converts the JSP document into a Java Servlet then the
servlet will be loaded |
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Java code is embedded between <% and %> |
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// file: hello.jsp |
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<html><head><title>example</title></head> |
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<body> |
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<% String visitor =
request.getParameter(“user”); |
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if
(visitor == null) visitor = “there”; |
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%> |
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Hello, <%= visitor %>! |
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</body> |
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</html> |
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Request parameters are passed into JSP pages
using normal HTTP parameter mechanisms (using GET and POST) |
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Therefore, for the hello.jsp: |
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If invoked with: http://host…/hello.jsp it will
print “Hello, World!” |
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If invoked with: http://host…/hello.jsp?user=Mary,
it will print: “Hello, Mary!” |
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<?xml version…> |
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<!DOCTYPE…etc> |
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<% response.setContentTyp("text/vnd.wap.wml") |
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%> |
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<wml> <card
title="MobileDate" |
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Date and Time Service<br/> |
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Date is: <%= new java.util.Date() %> |
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</card> |
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</wml> |
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Or you can use the PAGE directive… |
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Additional characters may appear after the
initial <%, such as !, =, or @ to further prescribe the meaning of the
tag |
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<%! Double radius = 3.5; %> |
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<%= 2 * Math.PI * radius %> |
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<%@ include file=“notice.html” %> |
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It is possible to create re-usable components
with JSP using Java Beans |
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Explore on your own! |
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If you don’t have access to an HTTP server, I’d
recommend that you install Jakarta-Tomcat for your personal use ….so you
explore Servlets and JSP further…. |
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http://jakarta.apache.org/tomcat |
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Notes