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Early interest focused on
using Java to write applets to run in a client's browser.
Java is becoming increasingly important as a language
for server programming.
The Java 2 Standard Edition contains classes in the java.net package
for creating Java
servers along traditional networking programming lines. This involves
creating sockets (transport endpoints) bound to TCP ports. Thus a Java server
may listen on a well-defined port (such as port 80) and read a raw
byte stream which contains HTTP requests, sending HTTP responses in an
output byte stream. One could construct a complete Java based HTTP
server for use on the WWW.
An alternative approach is to create a Java runtime environment which
can be connected to an existing Web server, and allows Java
components to be plugged into that environment. This hides the
details of how HTTP requests and responses are handled, and allows Java
components to be used by up-to-date industrial strength Web servers.
Java Servlets is a standard framework for these components.
A simple Java Servlet API is defined by Sun Microsystems as a
Java Enterprise
standard.
These notes describe my efforts to develop and deploy Java servlets on
Mandrake Linux.
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I followed the Java servlets tutorial in
PC Plus (September 2001).
as an introduction. This involved downloading the binary distribution of
the open source Java servlets engine known as Tomcat from the Apache
Project site.
The file jakarta-tomcat-3.2.3.zip was downloaded from
http://jakarta.apache.org/tomcat
and unpacked using the unzip command.
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To read the documentation I used the following commands:
TOMCAT_HOME=`pwd`/jakarta-tomcat-3.2.3 export TOMCAT_HOME
cd $TOMCAT_HOME/doc
netscape `pwd`/index.html
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I installed and started the software as described in the Tomcat User's Guide.
I then accessed the Tomcat home page locally using netscape to
access the URL http://localhost:8080. This gives more information on
the servlets development environment than in the magazine article,
as well as links to other servlet related Web sites.
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Somewhile later I discovered that you MUST have JAVA_HOME set in order to do
much useful. Tomcat will generate ClassNotFound errors, or similar,
and these will be sent to the client process for most SOAP calls.
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I then looked through the document Developing Applications With Tomcat
to get a rough idea what was involved in creating a simple servlet from
scratch. The document uses an IDE (Integrated Development Environment)
called "ant", but I decided I wanted to create a servlet from scratch
using just the Java SDK (and good old vi, of course).
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I followed the article quite closely in creating a Java source file
Hello.java. I then added each of the jar files in the Tomcat lib directory
to my CLASSPATH environment variable and tried to compile the code using
the command
javac Hello.java
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I found that the class to extend is called HttpServlet
(not HTTPServlet as in the article). Incidentally, I found the class
names using the commands
cd $TOMCAT_HOME/lib
$JAVA_HOME/bin/jar tf servlet.jar
I also had to include the line
import java.io.*;
at the top of the file which the article didn't mention explicitly.
I'm getting the hang of all this now ...
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Instead of creating a new Context entry in
server.xml, I found it is possible to create a new sub-directory
(dave) in an existing directory (webapps).
I copied the file Hello.class into $TOMCAT_HOME/webapps/dave/WEB-INF/classes.
When Tomcat is restarted it automatically creates a Context for each
sub-directory such as dave (see the Tomcat log files for startup information
which logs these directories).
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It is then possible to run the servlet via the following URL:
http://localhost:8080/dave/servlet/Hello
Success! My first Java servlet.
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