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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="startup.html">

  &project;

  <properties>
    <author email="yoavs@apache.org">Yoav Shapira</author>
    <title>Startup</title>
  </properties>

<body>


<section name="Server Startup">

<p>
This page describes how the Tomcat server starts up.  There are several
different ways to start tomcat, including:
</p>
<ul>
  <li>From the command line.</li>
  <li>From a Java program as an embedded server.</li>
  <li>Automatically as a Windows service.</li>
</ul>

<subsection name="description">
<p>
A <a href="startup/serverStartup.txt">text description</a> of the startup
procedure created for Tomcat 5. The updated version of this description for
Tomcat 11 will be included in the updated diagrams and diagram descriptions in
the following section. This text file will be removed when that update is
complete.
</p>
</subsection>

<subsection name="diagram">
<p>
The <a href="startup/serverStartup.pdf">UML sequence diagram</a> of the startup
procedure created for Tomcat 5 is gradually being replaced with updated diagrams
based on Tomcat 11. The scope of these diagrams may be adjusted as they are
produced.
</p>
<p>
A series of UML diagrams have been created to document the start-up process for
Tomcat.
</p>
<p>
<a href="startup/1_overview.png">Diagram 1</a> shows an overview of how Tomcat
start, serves requests and then stops. Once the class loaders have been
initialized, Tomcat parses server.xml using the Digester and the Digester
creates the objects defined in server.xml, configures them using the property
values defined in server.xml and the starts the Server. The main Java thread
waits in the await() method for a shutdown signal. Once a shutdown signal is
received, the Server object is stopped and then destroyed. The JVM then exits.
</p>
<p>
<a href="startup/2_catalina_init.png">Diagram 2</a> shows how Tomcat initalizes
the objects created by the Digester in the previous step and when additional key
objects are created. A Server may have several Services although it typically
only has one. Each Service may have multiple Connectors. A Connector instance is
associated with a single Protocol instance and a single CoyoteAdapter instance.
</p>
<p>
<a href="startup/3_catalina_start_1.png">Diagram 3</a> shows how Tomcat starts
the objects created by the Digester that were initialized in the previous step.
This diagram also shows when lifecycle events are fired. There is more detail to
the starting of the Engine (and other Containers) which is shown in the
following diagram.
</p>
<p>
<a href="startup/4_catalina_start_2.png">Diagram 4</a> shows how Containers
(Engines, Hosts, Contexts and Wrappers) start along with any supporting
Clusters, Realms and Valves.
</p>
<p>
<a href="startup/5_catalina_start_3.png">Diagram 5</a> shows the start process
for Context elements as it is rather more involved that the other Containers.
</p>
<p>
<a href="startup/6_catalina_host_config.png">Diagram 6</a> shows how the
HostConfig component responds to lifecycle events triggered by the Host to
deploy web applications to the Host.</p>
<p>
<a href="startup/7_catalina_context_config.png">Diagram 7</a> shows how the
ContextConfig component responds to lifecycle events triggered by the Context to
parse the global and application provided configuration files to create a merged
web.xml file that is then used, along with other settings, to configure the web
application.
</p>
</subsection>

<subsection name="comments">
<p>
The startup process can be customized in many ways, both
by modifying Tomcat code and by implementing your own
LifecycleListeners which are then registered in the server.xml
configuration file.
</p>

</subsection>

</section>


</body>
</document>
