Tomcat is a pure java approach to a web server. Tomcat is a pure java web server that employes:

• Catalina - a servlet container...
• Coyote - a HTTP connector...and
• Jasper - a Java Server Page engine.

It was named Tomcat by James Duncan Davidson, its writer, because a Tomcat is something that can fend for itself.

The Tomcat server is made up of several entities. Each of which has a seperate and distinct purpose.

Each entity also has a one to many relationship with it's children. For this reason there can be many services inside a server, many engines inside a service and so on.

Linux and linux type file systems are structured by function while other OSs... namely Windows... are structured by darts. Finding the Tomcat files in your file system may seem intimidating but you can figure it out by looking for some key features.

First thing to find is CATALINA_HOME

This is Tomcats home directory and it's easy to find because this structure has one thing that none of the other structures has...

The bin directory... that's where the startup scripts are...

Locate this directory and you found CATALINA_HOME

Try this:

   ~$ sudo find / -path "*/tomcat9/bin"    /usr/share/tomcat9/bin

This structure is from a Debian Buster system. Your distro may be different... unless of course... it is Debian 10. In any event, the Catalina Home stucture should be the same. The path leading to it is different.

The next thing to find is CATALINA_BASE

Like Catalina Home Catalina Base has uniqe fetures also.... one obvious feature... the webapps directory.

This is where Tomcat houses the applications you develop.

In webapps there is a directory for every Host defined in the server.xml file. Under that... is the applications you deploy for that host. The hosts defined in the server.xml file are virtual hosts. The default is Catalina.

Find tomcat9/webapps and you have found CATALINA_BASE

Try this:

   $ sudo find / -path "*/tomcat9/webapps"    /var/lib/tomcat9/webapps

To understand the proces of database connection pooling in Tomcat 7, read these...

• JNDI Datasource HOW-TO
• The Context Container
• The Host Container
• Commons DBCP Docs
• The Tomcat JDBC Connection Pool

A valve is a component that is inserted into the processing pipeline for a specific scope (Engine, Host, Context).

WEB.XML - Web Application Deployment Descriptor
<env-entry> - an environment variable that can be called from inside servlets
<resource-ref> - package and class name to a resource (factory?)
<resource-env-ref> - not sure.

Tomcat will use the resource identified by <resource-ref> to create the resource if no
further information is needed.

---IF NOT---

CONTEXT.XML
If Tomcat can not identify the resource "factory" OR additional information is needed
additional info should be entered in the "context.xml" file

Context information can be specified in either the <Context> element in the "Server.xml" file
OR
in the application specific "META-INF/context.xml" file.