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Tomcat example source code file (deployer-howto.xml)
This example Tomcat source code file (deployer-howto.xml) is included in the DevDaily.com
"Java Source Code
Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.
The Tomcat deployer-howto.xml source code
<?xml version="1.0"?>
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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="deployer-howto.html">
&project;
<properties>
<author>Allistair Crossley
<title>Tomcat Web Application Deployment
</properties>
<body>
<section name="Table of Contents">
<ul>
<li>Introduction
<li>Installation
<li>A word on Contexts
<li>Deployment on Tomcat startup
<li>Deploying on a running Tomcat server
<li>Deploying using the Tomcat Manager
<li>Deploying using
the Tomcat Client Deployer</a>
</ul>
</section>
<section name="Introduction">
<p>
Deployment is the term used for the process of installing a web
application (either a 3rd party WAR or your own custom web application)
into the Tomcat server.
</p>
<p>
Web application deployment may be accomplished in a number of ways
within the Tomcat server.
<ul>
<li>Statically; the web application is setup before Tomcat is started
<li>
Dynamically; in conjunction with the Tomcat Manager web application or
manipulating already deployed web applications
</li>
</ul>
</p>
<p>
The Tomcat Manager is a tool that allows URL-based web application
deployment features. There is also a tool called the Client Deployer,
which is a command shell based script that interacts with the Tomcat
Manager but provides additional functionality such as compiling and
validating web applications as well as packaging web application into
web application resource (WAR) files.
</p>
</section>
<section name="Installation">
<p>
There is no installation required for static deployment of web
applications as this is provided out of the box by Tomcat. Nor is any
installation required for deployment functions with the Tomcat Manager,
although some configuration is required as detailed in the
Tomcat Manager manual. An installation is however required if you wish
to use the Tomcat Client Deployer (TCD).
</p>
<p>
The TCD is not packaged with the Tomcat core
distribution, and must therefore be downloaded separately from
the Downloads area. The download is usually labelled
<i>apache-tomcat-6.0.x-deployer.
</p>
<p>
TCD has prerequisites of Apache Ant 1.6.2+ and a Java installation.
Your environment should define an ANT_HOME environment value pointing to
the root of your Ant installation, and a JAVA_HOME value pointing to
your Java installation. Additionally, you should ensure Ant's ant
command, and the Java javac compiler command run from the command shell
that your operating system provides.
</p>
<ol>
<li>Download the TCD distribution
<li>
The TCD package need not be extracted into any existing Tomcat
installation, it can be extracted to any location.
</li>
<li>Read Using the
Tomcat Client Deployer</a>
</ol>
</section>
<section name="A word on Contexts">
<p>
In talking about deployment of web applications, the concept of a
<i>Context is required to be understood. A Context is what Tomcat
calls a web application.
</p>
<p>
In order to configure a Context within Tomcat a <i>Context Descriptor
is required. A Context Descriptor is simply an XML file that contains
Tomcat related configuration for a Context, e.g naming resources or
session manager configuration. In earlier versions of
Tomcat the content of a Context Descriptor configuration was often stored within
Tomcat's primary configuration file <i>server.xml but this is now
discouraged (although it currently still works).
</p>
<p>
Context Descriptors not only help Tomcat to know how to configure
Contexts but other tools such as the Tomcat Manager and TCD often use
these Context Descriptors to perform their roles properly.
</p>
<p>
The locations for Context Descriptors are;
<ol>
<li>$CATALINA_HOME/conf/[enginename]/[hostname]/context.xml
<li>$CATALINA_HOME/webapps/[webappname]/META-INF/context.xml
</ol>
Files in (1) are named [webappname].xml but files in (2) are named
context.xml. If a Context Descriptor is not provided for a Context,
Tomcat configures the Context using default values.
</p>
</section>
<section name="Deployment on Tomcat startup">
<p>
If you are not interested in using the Tomcat Manager, or TCD,
then you'll need to deploy your web applications
statically to Tomcat, followed by a Tomcat startup. The location you
deploy web applications to for this type of deployment is called the
<code>appBase which is specified per Host. You either copy a
so-called <i>exploded web application, i.e non-compressed, to this
location, or a compressed web application resource .WAR file.
</p>
<p>
The web applications present in the location specified by the Host's
(default Host is "localhost") <code>appBase attribute (default
appBase is "$CATALINA_HOME/webapps") will be deployed on Tomcat startup
only if the Host's <code>deployOnStartup attribute is "true".
</p>
<p>
The following deployment sequence will occur on Tomcat startup in that
case:
</p>
<ol>
<li>Any Context Descriptors will be deployed first.
<li>
Exploded web applications not referenced by any Context
Descriptor will then be deployed. If they have an associated
.WAR file in the appBase and it is newer than the exploded web application,
the exploded directory will be removed and the webapp will be
redeployed from the .WAR
</li>
<li>.WAR files will be deployed
</ol>
<p>
Note again that for each deployed web application, a
Context Descriptor will be created <i>unless one exists already.
</p>
</section>
<section name="Deploying on a running Tomcat server">
<p>
It is possible to deploy web applications to a running Tomcat server.
</p>
<p>
If the Host <code>autoDeploy attribute is "true", the Host will
attempt to deploy and update web applications dynamically, as needed,
for example if a new .WAR is dropped into the <code>appBase.
For this to work, the Host needs to have background processing
enabled which is the default configuration.
</p>
<p>
<code>autoDeploy set to "true" and a running Tomcat allows for:
</p>
<ul>
<li>Deployment of .WAR files copied into the Host appBase.
<li>
Deployment of exploded web applications which are
copied into the Host <code>appBase.
</li>
<li>
Re-deployment of a web application which has already been deployed from
a .WAR when the new .WAR is provided. In this case the exploded
web application is removed, and the .WAR is expanded again.
Note that the explosion will not occur if the Host is configured
so that .WARs are not exploded with a <code>unpackWARs
attribute set to "false", in which case the web application
will be simply redeployed as a compressed archive.
</li>
<li>
Re-deployment of a web application if the /WEB-INF/web.xml file (or any
other resource defined as a WatchedResource) is updated.
</li>
<li>
Re-deployment of a web application if the Context Descriptor file from which
the web application has been deployed is updated.
</li>
<li>
Re-deployment of a web application if a Context Descriptor file (with a
filename corresponding to the Context path of the previously deployed
web application) is added to the
<code>$CATALINA_HOME/conf/[enginename]/[hostname]/
directory.
</li>
<li>
Undeployment of a web application if its document base (docBase)
is deleted. Note that on Windows, this assumes that anti-locking
features (see Context configuration) are enabled, otherwise it is not
possible to delete the resources of a running web application.
</li>
</ul>
<p>
Note that web application reloading can also be configured in the loader, in which
case loaded classes will be tracked for changes.
</p>
</section>
<section name="Deploying using the Tomcat Manager">
<p>
The Tomcat Manager is covered in its <a href="manager-howto.html">own manual page.
</p>
</section>
<section name="Deploying using the Client Deployer Package">
<p>
Finally, deployment of web application may be achieved using the
Tomcat Client Deployer. This is a package which can be used to
validate, compile, compress to .WAR, and deploy web applications to
production or development Tomcat servers. It should be noted that this feature
uses the Tomcat Manager and as such the target Tomcat server should be
running.
</p>
<p>
It is assumed the user will be familar with Apache Ant for using the TCD.
Apache Ant is a scripted build tool. The TCD comes pre-packaged with a
build script to use. Only a modest understanding of Apache Ant is
required (installation as listed earlier in this page, and familiarity
with using the operating system command shell and configuring
environment variables).
</p>
<p>
The TCD includes Ant tasks, the Jasper page compiler for JSP compilation
before deployment, as well as a task which
validates the web application Context Descriptor. The validator task (class
<code>org.apache.catalina.ant.ValidatorTask) allows only one parameter:
the base path of an exploded web application.
</p>
<p>
The TCD uses an exploded web application as input (see the list of the
properties used below). A web application that is programatically
deployed with the deployer may include a Context Desciptor in
<code>/META-INF/context.xml.
</p>
<p>
The TCD includes a ready-to-use Ant script, with the following targets:
</p>
<ul>
<li>
<code>compile (default): Compile and validate the web
application. This can be used standalone, and does not need a running
Tomcat server. The compiled application will only run on the associated
Tomcat 5.5.x server release, and is not guaranteed to work on another
Tomcat release, as the code generated by Jasper depends on its runtime
component. It should also be noted that this target will also compile
automatically any Java source file located in the
<code>/WEB-INF/classes folder of the web application.
<li>
<code>deploy: Deploy a web application (compiled or not) to
a Tomcat server.
</li>
<li>undeploy: Undeploy a web application
<li>start: Start web application
<li>reload: Reload web application
<li>stop: Stop web application
</ul>
<p>
In order for the deployment to be configured, create a file
called <code>deployer.properties in the TCD installation
directory root. In this file, add the following name=value pairs per
line:
</p>
<p>
Additionally, you will need to ensure that a user has been
setup for the target Tomcat Manager (which TCD uses) otherwise the TCD
will not authenticate with the Tomcat Manager and the deployment will
fail. To do this, see the Tomcat Manager page.
</p>
<ul>
<li>
<code>build: The build folder used will be, by default,
<code>${build}/webapp/${path}. After the end of the execution
of the <code>compile target, the web application .WAR will be
located at <code>${build}/webapp/${path}.war.
</li>
<li>
<code>webapp: The directory containing the exploded web application
which will be compiled and validated. By default, the folder is
<code>myapp.
</li>
<li>
<code>path: Deployed context path of the web application,
by default <code>/myapp.
</li>
<li>
<code>url: Absolute URL to the Tomcat Manager web application of a
running Tomcat server, which will be used to deploy and undeploy the
web application. By default, the deployer will attempt to access
a Tomcat instance running on localhost, at
<code>http://localhost:8080/manager.
</li>
<li>
<code>username: Tomcat Manager username (user should have a role of
manager)
</li>
<li>password: Tomcat Manager password.
</ul>
</section>
</body>
</document>
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