Running a Servlet under Tomcat

Download and install Tomcat

1. Download jakarta-tomcat-3.2.4.zip from http://jakarta.apache.org/builds/jakarta-tomcat/release/v3.2.4/bin/. I downloaded it to the top level of the C:drive. (The actual location doesn't matter.)
2. Unzip it. It creates a subdirectory called jakarta-tomcat-3.2.4.

Set the JAVA_HOME environment variable

When setting environment variables, do not use quotatation marks and do not put spaces around the equal sign when using the set command in a Command Prompt window. For example, to set JAVA_HOME, write

set JAVA_HOME=C:\JBuilder5\jdk1.3.1

Start Tomcat and access a file

1. Start a Command Prompt window.
2. Change directory to the bin subdirectory of the Tomcat directory and run the startup command. In my case,

   cd C:\jakarta-tomcat-3.2.4\bin
startup

3. A new Command Prompt window will be opened with Tomcat running. Note that when Tomcat starts, it sets two additional environment variables.
   1. It sets TOMCAT_HOME to the Tomcat home directory, in my case to C:\jakarta-tomcat-3.2.4. (Note that in Windows, %TOMCAT_HOME% refers to the contents of the TOMCAT_HOME environment variable.)
   2. It sets CLASSPATH to include %TOMCAT_HOME%\lib\servlet.jar.

Two things worth noting about this URL.

1. The host is localhost:8080. (By default Tomcat listens on port 8080.)
2. The address (i.e., path) is examples/servlets/index.html. When Tomcat sees a URL, it consults its server.xml file (which is in %TOMCAT_HOME%/conf) to see if the path in the URL has been defined as a web application. In this case it has been. The file %TOMCAT_HOME%/conf/server.xml contains the following near the bottom.

   
           <Context path="/examples"
                    docBase="webapps/examples"
                    crossContext="false"
                    debug="0"
                    reloadable="true" >
           </Context>
   

   This is a mapping from a URL address path to an internal location.

   1. The path attribute defines /examples as a URL address which should be mapped to a special place on the disk and which may be associated with a Servlet.
   2. The docBase attribute defines webapps/examples as the place on the disk to associate with the path /examples.
   3. In other words, the above <Context> tag tells Tomcat to map

      http://localhost:8080/examples/

      to

      %TOMCAT_HOME%/webapps/examples/

      So when the user asks for

      http://localhost:8080/examples/servlets/index.html

      Tomcat actually access the file

      %TOMCAT_HOME%/webapps/examples/servets/index.html

   4. There is such a file, which comes with the Tomcat download. When Tomcat is unzipped, it creates an examples directory as a subdirectory of %TOMCAT_HOME%/webapps. That examples directory has a servlets subdirectly, which has an index.html file in it.

Run a Servlet

1. One of the links in the file http://localhost:8080/examples/servlets/index.html is to ../servlet/HelloWorldExample. On first glance, this looks like it should be referring to a file at %TOMCAT_HOME%/webapps/examples/servlet/HelloWorldExample. But there is no such file. In fact, there is no such directory as %TOMCAT_HOME%/webapps/examples/servlet/.
2. Instead, by convention, a reference to what appears to be a servlet directory at the top level of a mapped webapp address means: execute the indicated servlet. In this case, execute the servlet called HelloWorldExample.
3. Servlets are simply .class files, i.e., compiled .java files.
4. Servlet files are stored in the WEB-INF/classes subdirectory of the main web application directory. In this case the .class files for the examples web app is stored in %TOMCAT_HOME%/webapps/examples/WEB-INF/classes.
5. So when the user requests

   http://localhost:8080/examples/servlet/HelloWorldExample

   Tomcat runs

   %TOMCAT_HOME%/webapps/examples/WEB-INF/classes/HelloWorldExample.class

Create and run your own Servlet