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<?xml version="1.0"?>
<document>
<properties>
<title>App Launching</title>
<author email="bob@eng.werken.com">bob mcwhirter</author>
</properties>
<body>
<section name="Introduction">
<subsection name="Purpose">
<p>
In order to reduce the number of classloading projects,
<code>classworlds</code> replaces <code>forehead</code>
for application launching.
</p>
<p>
The main problems to solve in application launching include
locating all of application's JARs, configuring the initial
classloaders, and invoking the <code>main</code> entry method.
</p>
<p>
The launcher facilities of <code>classworlds</code> simplify
the process of locating application jars. A common idiom is
to have a script which starts the JVM with only the
<code>classworlds.jar</code> in the classpath and a system
property to specify the location of a launcher configuration.
Additionally, typically a property specifying the installation
location is passed on the command-line.
</p>
<source><![CDATA[
$JAVA_HOME/bin/java \
-classpath $APP_HOME/lib/classworlds-1.0.jar \
-Dclassworlds.conf=$APP_HOME/etc/classworlds.conf \
-Dapp.home=$APP_HOME \
org.codehaus.classworlds.Launcher \
$*
]]></source>
</subsection>
</section>
<section name="Configuration">
<subsection name="Entry Definition">
<p>
The entry-point class and realm must be specified
using the <code>main is</code> directive before
specifying realm definitions.
</p>
<source><![CDATA[
main is com.werken.projectz.Server from app
]]></source>
</subsection>
<subsection name="Realm Definitions">
<p>
At least one <code>classworlds</code> realm must be defined
within the configuration file. The syntax for starting a
realm definition is <code>[realm.name]</code>. All lines
following the realm header are considered directives for
that realm. The realm definition continues either until
another realm is defined or until the end of the file is
reached.
</p>
<source><![CDATA[
[realm.one]
...
...
[realm.two]
...
...
[realm.three]
...
...
]]></source>
<p>
Within a realm definition, two directives are available:
<code>load</code> and <code>import</code>.
</p>
<p>
The <code>load</code>
directive specifies a class source to be used for loading
classes in the realm. Any loaded source that ends with
the <code>/</code> character is considered a directory
hierarchy of classes and resources and all others are
considered to be JAR files. System properties may be
referred to using <code>${propname}</code> notation.
The <code>load</code> directive is equivelent to the
<code>addConstituent(..)</code> method of <code>ClassRealm</code>.
</p>
<source><![CDATA[
[app]
load ${app.home}/lib/myapp.jar
load ${app.home}/lib/xerces.jar
load ${tools.jar}
]]></source>
<p>
The <code>import</code> directive specifies that certain
packages should be imported and loaded by way of another
realm. The <code>import</code> directive is equivelent
to the <code>importFrom(..)</code> method of
<code>ClassRealm</code>.
</p>
<source><![CDATA[
[app]
...
[subcomponent]
import com.werken.projectz.Foo from [app]
...
]]></source>
</subsection>
<subsection name="Entry point methods">
<p>
<code>classworlds</code> can be used to invoke any existing
application's <code>main()</code> method. Using the standard
entry point does not allow for gaining access to the
<code>ClassWorld</code> of the application, but not all
applications will need it at run-time.
</p>
<p>
For those applications that do require the <code>ClassWorld</code>
instance, an alternative entry-point method signature can be
provide. Simply add a <code>ClassWorld</code> parameter to
the standard <code>main</code> parameter list.
</p>
<source><![CDATA[
public class MyApp
{
public static void main(String[] args,
ClassWorld world)
{
...
}
}
]]></source>
</subsection>
</section>
</body>
</document>
|
