Java Servlets - Programming Experiments
The links listed below refer to the author's initial experiments with Java
Servlets. For the links to work properly (in a local environment) the following
requirements have to be met:
-
a web server with support for servlets has to be running on the local host
under port number 9090 (the author is using
Gefion's LiteWebServer 2.2.1 for that purpose);
-
if the default servlet invocation mechanism foreseen by the LiteWebServer
has been disabled (e.g., for security reasons), any of the servlets shown
below have to be configured explicitly;
-
all servlets (and any additional files which may be needed for a proper servlet
execution) have to be installed in a subdirectory where they can be found
by the server. A list of all these files can be found at the end of this
page.
Please, also consider my "Hints for Reading"
and the "List of Recent Changes".
LiteWebServer Configuration
The following modifications have to be applied to the given files in order
to instruct the LiteWebServer to invoke a servlet whenever requested:
-
(installdir)/config/rules.properties
-
add the following lines:
/Servlet_00=Servlet_00
/Servlet_01=Servlet_01
/Servlet_02=Servlet_02
/Servlet_03=Servlet_03
/Servlet_04=Servlet_04
These modifications instruct the LiteWebServer to invoke on of the given
servlets whenever the URI of an HTTP request starts with the corresponding
prefix. It is also assumed that the default rule
/=file
is still active;
-
(installdir)/config/servlets.properties
-
add the following lines:
servlet.Servlet_00.code=Servlet_00
servlet.Servlet_01.code=Servlet_01
servlet.Servlet_02.code=Servlet_02
servlet.Servlet_03.code=Servlet_03
servlet.Servlet_04.code=Servlet_04
These modifications associate a concrete servlet class with a given servlet
name;
In both cases, (installdir) has to be replaced
by the access path for the installation directory of LiteWebServer on your
local system.
Using a configuration as shown above, any servlet class files will
have to be copied into
(installdir)/servlets/ and all associated
data files into
(installdir)/html/default. Again,
(installdir) denotes the LiteWebServer
installation directory.
Do not forget to restart LiteWebServer whenever any of the servlet class
files has changed. Otherwise, these changes will not have any effect.
Servlet Experiments
After this initial preparation, following the links shown below should work
as foreseen. Please note, that you cannot test the following links over
the internet - you must install a (servlet capable) HTTP server locally (as
described above)!
-
Servlet_00 - first experiments
with Java Servlets (Output
Example)
the first "experiment" demonstrates some basic programming techniques for
servlets: it creates a simple HTML document (using numerous "println" statements)
which contains a table with the values of several "CGI variables";
-
Servlet_01 - displays the
contents of several "CGI variables" (Output
1,
2)
when invoked without any parameters (within the HTTP "Get" request), "Servlet_01"
responds with a HTML document that (is loaded from disk and) contains a form
with numerous input elements and a "submit" button, which sends the actual
state of all these input elements back to the server. Now, "Servlet_01" examines
any given request parameters and returns a HTML file with a table of their
values;
-
Servlet_02 - lists all
HTTP request headers (Output
Example)
"Servlet_02" creates a HTML document with any headers sent along with a given
HTTP request;
Note: from time to time, image files which belong to the HTML documents sent
as the response to a HTTP request get "lost" and will then not be shown by
the browser. Presumably, this issue is due to the simplicity of the
abovementioned servlets (which are unable to handle several requests
simultaneously). Just resubmit your request and - with a little bit of luck
- you will get the foreseen result.
Required Files
In order to run the experiments shown above, the following files have to
be installed into the default "document" (or the "servlet") directory of
your LiteWebServer:
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