donaldp 2002/11/10 06:43:38
Modified: fortress/src/xdocs lifecycle-extensions.xml
Log:
Fix docs
Revision Changes Path
1.4 +99 -99
jakarta-avalon-excalibur/fortress/src/xdocs/lifecycle-extensions.xml
Index: lifecycle-extensions.xml
===================================================================
RCS file:
/home/cvs/jakarta-avalon-excalibur/fortress/src/xdocs/lifecycle-extensions.xml,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
--- lifecycle-extensions.xml 26 Jul 2002 16:12:44 -0000 1.3
+++ lifecycle-extensions.xml 10 Nov 2002 14:43:38 -0000 1.4
@@ -21,13 +21,13 @@
metainfo which tells the ComponentManager how a particular Component
should be treated
during it's life.
</p>
-
+
<p>
This metainfo allows the developer to separate the various concerns
involved when
writing a Component, often termed SoC and IoC (Separation of Concerns
and Inversion of
Control) and is one of primary advantages of using Avalon.
</p>
-
+
<p>
Sometimes it's useful to extend this development paradigm from the
framework level
into the application domain, to create customized lifecycle extensions
that are called
@@ -52,7 +52,7 @@
The possibilities and number of extensions are only limited by the
requirements of your
particular application domain.
</p>
-
+
<p>
This document describes how to add new lifecycle extensions using
<strong>Fortress</strong>.
This document assumes a knowledge of what an Avalon lifecycle is, and a
basic understanding
@@ -60,65 +60,65 @@
Component and ComponentManager can also be freely interpreted as Service
and ServiceManager
by the reader.
</p>
-
+
<p>
<note>As at the time of writing, Fortress is the only Avalon container
that
supports lifecycle extensions, which means Components that use this
feature will most likely
only work as expected with Fortress, and not with the other Avalon
containers
(ExcaliburComponentManager, Phoenix, Merlin, Tweety, etc)</note>
</p>
-
+
<p>
Support for lifecycle extensions in the other Avalon containers is
technically possible but
has not yet been discussed. Please check with the Avalon developer
mailing list if you use
one of these containers and would like to use lifecycle extensions.
</p>
-
+
</s1>
-
+
<s1 title="How do I extend a Component's lifecycle ?">
<p>
Extending a Component's lifecycle is straightforward. An overview of the
process
follows:
</p>
-
+
<ol>
<li>Define the new component interface</li>
-
+
<p>
Create the new interface defining the operations that should be called
upon components
that implement this interface. Using the previously mentioned
examples, this would be
your <code>SecurityManageable</code>, <code>Cacheable</code>,
<code>Decryptable</code>,
<code>Recycleable</code> interfaces.
</p>
-
+
<li>Define an extension object that calls upon the methods defined in
the new interface,
during one or more of the pre-defined phases of component's
lifecycle</li>
-
+
<p>
Create a class that implements <code>LifecycleExtension</code>, that
tests any given
component for the above defined interface (and others if applicable),
invoking methods
defined in that interface.
</p>
-
+
<li>Register the extension object with Fortress'
<code>LifecycleExtensionManager</code></li>
-
+
<p>
Create an instance of the class defined in the previous step, and
register it with a
<code>LifecycleExtensionManager</code>, using either the default
manager available inside
of your container, or an externally created manager that is later
given to the container
to use.
</p>
-
+
<li>Implement the new component interface on your component</li>
-
+
<p>
Add the new <code>implements</code> clause to your Component, or
Component implementation,
and write any methods defined in the implemented interface.
</p>
-
+
<li><code>lookup()/select()/release()</code> components as normal</li>
-
+
<p>
Proceed as normal. Checking for extensions is done implicitly within
Fortress. Once
lifecycle extensions are registered they will be invoked on any
implementing components
@@ -126,47 +126,47 @@
</p>
</ol>
</s1>
-
+
<s1 title="When can a Component's lifecycle be extended ?">
<p>
The life of any component can be broken down to the following phases:
</p>
-
+
<ol>
<li>Creation</li>
-
+
<p>
When the Component is actually instantiated.
</p>
-
+
<li>Access</li>
-
+
<p>
When the Component is accessed via a ComponentManager/Selector
(<code>lookup()/select()</code>).
</p>
-
+
<li>Release</li>
-
+
<p>
When the Component is released via a ComponentManager/Selector
(<code>release()</code>).
</p>
-
+
<li>Destruction</li>
-
+
<p>
When the Component is decommissioned, ready for garbage collection.
</p>
-
+
</ol>
-
+
<p>
<note>A Component will go through it's Creation and Destruction phase
only once. Since
<code>ComponentHandler</code> classes can implement different handling
strategies
(Poolable, ThreadSafe, etc), the access and release phases of a
component can be
done multiple times.</note>
</p>
-
+
<p>
Lifecycle extensions can be added to any of the above defined phases.
This allows
you to choose when your particular extension will be executed.
@@ -185,13 +185,13 @@
</p>
</s1>
-
+
<s1 title="Which interfaces and classes do I need to use ?">
-
+
<p>
Support for lifecycle extensions in Fortress is done using the following
classes/interfaces.
</p>
-
+
<s2 title="The Component Extension Interface">
<p>
This interface specifies the business particular extension components
will be tested for.
@@ -204,41 +204,41 @@
can be kept separate from the Container itself.
</p>
</s2>
-
+
<s2 title="The LifecycleExtension Interface">
-
+
<p>
Component extensions are invoked via a Lifecycle extension object.
Lifecycle extension
objects are managed via a <code>LifecycleExtensionManager</code> class
and essentially
test for a particular Component extension interface, and appropriately
call methods defined
in that interface.
</p>
-
+
<p>
All Lifecycle extension objects must implement the
<code>LifecycleExtension</code> interface.
The <code>LifecycleExtension</code> interface defines 4 methods that are
called upon to allow
an implementor to extend a component's lifecycle.
</p>
-
+
<p>
- The 4 methods (<code>create</code>, <code>destroy</code>,
<code>access</code> and
+ The 4 methods (<code>create</code>, <code>destroy</code>,
<code>access</code> and
<code>release</code>) are invoked by a manager class from inside
Fortress. Each method
accepts 2 parameters, the particular Component instance being extended,
and the container
<code>Context</code>.
</p>
-
+
<p>
The container <code>Context</code> is passed as a parameter to provide
access to any
miscellaneous objects that might be needed during extension code (to
make use of this feature
the container Context will need to be initialized with references and
passed to the
- <code>ContextBuilder</code> during Fortress' startup sequence).
+ <code>FortressConfig</code> during Fortress' startup sequence).
</p>
-
+
<p>
Each method may throw an exception to indicate an error, which will be
logged, but will
not terminate other extensions from being executed on that Component.
</p>
-
+
<source>
/**
* LifecycleExtension interface. This interface defines the methods that
@@ -248,7 +248,7 @@
public interface LifecycleExtension
{
/**
- * Create, called when the given component is being
+ * Create, called when the given component is being
* instantiated.
*
* @param component a Component instance
@@ -257,7 +257,7 @@
*/
void create( Object component, Context context )
throws Exception;
-
+
/**
* Destroy, called when the given component is being
* decommissioned.
@@ -268,7 +268,7 @@
*/
void destroy( Object component, Context context )
throws Exception;
-
+
/**
* Access, called when the given component is being
* accessed (ie. via lookup() or select()).
@@ -279,7 +279,7 @@
*/
void access( Object component, Context context )
throws Exception;
-
+
/**
* Release, called when the given component is being
* released (ie. by a CM or CS).
@@ -292,117 +292,117 @@
throws Exception;
}
</source>
-
+
<p>
- Many extensions will not require implementation of every method defined
in the
+ Many extensions will not require implementation of every method defined
in the
above interface, for that reason, there's a
<code>AbstractLifecycleExtension</code>
convenience class available which provides default (empty)
implementations of each
method which you can extend from. This allows you to implement only the
methods
necessary for your particular extension.
</p>
-
+
</s2>
-
+
<s2 title="The LifecycleExtensionManager class">
-
+
<p>
The <code>LifecycleExtensionManager</code> class provides default
management of
extension implementations and an API which ComponentManager/Selector's
can call
upon to execute them.
</p>
-
+
<p>
The LifecycleExtensionManager class API is too big to list here, instead
please look at
the following <link
href="http://jakarta.apache.org/avalon/excalibur/fortress/api/org/apache/excalibur/fortress/lifecycle/LifecycleExtensionManager.html";>link</link>.
It essentially defines
4 methods for executing extension objects at the various phases of a
component's lifecycle,
and several methods for registering extension objects with the manager.
</p>
-
+
<p>
The <code>LifecycleExtensionManager</code> class will operate safely in
multithreaded
environments, and allows you to add/remove extensions to a running
system.
</p>
-
+
<p>
By default, all Fortress based containers will be initialized with a
default
<code>LifecycleExtensionManager</code> that contains no extensions. You
can alternatively
provide a pre-configured LifecycleExtensionManager to your Container via
the
- ContextBuilder class (<code>ContainerConstants.EXTENSION_MANAGER</code>
key) if you like.
+ FortressConfig class (<code>ContainerConstants.EXTENSION_MANAGER</code>
key) if you like.
</p>
-
+
<p>
To add a new lifecycle extension object to the manager simply call the
method
<code>LifecycleExtensionManager.addExtension()</code>. Methods also
exist for removing
and iterating through the currently available extensions.
</p>
</s2>
-
+
<s2 title="FortressComponentManager/FortressComponentSelector">
-
+
<p>
Fortress' inbuilt Component Manager/Selector/Factory code will
automatically call
- upon the LifecycleExtensionManager class at each phase in a Component's
life at the
+ upon the LifecycleExtensionManager class at each phase in a Component's
life at the
following predefined times:
</p>
-
+
<ol>
<li>Access</li>
-
+
<p>
Called inside the ComponentManager, after the component has been
retrieved
from it's handler, but before it's returned to the invoker of
<code>lookup()/select()</code>.
</p>
-
+
<li>Release</li>
-
+
<p>
Called inside the ComponentManager, before the component is passed
back to
it's handler to be disposed/pooled/etc.
</p>
-
+
<li>Creation</li>
-
+
<p>
Called inside the ComponentFactory, before <code>initialize()</code>.
</p>
-
+
<li>Destruction</li>
-
+
<p>
Called inside the ComponentFactory, after <code>dispose()</code>.
</p>
</ol>
-
+
<p>
<note>, components created via Fortress' ComponentHandler classes
directly
will bypass the logic for <code>access</code> and <code>release</code>
extensions. This is
because the code performing this logic is located in the
ComponentManager/Selector classes
(independent from all handlers).</note>
</p>
-
+
</s2>
-
+
</s1>
-
+
<s1 title="An Example">
-
+
<p>
Let's look at a simple example. The following is also available as a
working sample
in Fortress' examples directory.
</p>
-
+
<p>
Our example implements a Lifecycle extension for passing a
<code>SecurityManager</code> to
Components. We'll call it the <code>SecurityManageable</code> interface.
</p>
-
+
<s2 title="Define the component extension interface">
-
+
<p>
First we define the new Component extension interface.
</p>
-
+
<source>
/**
* Simple custom lifecycle extension interface for supplying a component
@@ -419,19 +419,19 @@
throws SecurityException;
}
</source>
-
+
</s2>
-
+
<s2 title="Create the lifecycle extensions class">
-
+
<p>
Next we define the actual extension implementation which invokes the
<code>secure()</code>
method. We extend from <code>AbstractLifecycleExtension</code> since we
only want
<code>secure()</code> to be invoked upon each access (ie. lookup()) to
the component, and
- don't need to implement the other 3 LifecycleExtension methods (create,
release, and
+ don't need to implement the other 3 LifecycleExtension methods (create,
release, and
destroy).
</p>
-
+
<source>
/**
* Some custom extensions for this container's components.
@@ -459,28 +459,28 @@
}
}
</source>
-
+
<p>
<note>An extension class may run components through any given number of
extensions, and are not limited to just one.</note>
</p>
-
+
</s2>
-
+
<s2 title="Register the lifecycle extensions class">
-
+
<p>
We then inform our container about the extension. This could be done in
several different
ways, for simplicity we'll extend <code>initialize()</code> and add it
to the
<code>LifecycleExtensionManager</code> there.
</p>
-
+
<p>
(an alternative might be to initialize a LifecycleExtensionManager
before creating the
- container and pass it in via the
<code>ContextBuilder.setExtensionManager()</code> method,
+ container and pass it in via the
<code>FortressConfig.setExtensionManager()</code> method,
or to create a LifecycleExtensionManager subclass that includes the
extension preset)
</p>
-
+
<source>
/**
* Simple container that includes custom lifecycle extensions.
@@ -492,22 +492,22 @@
throws Exception
{
super.initialize();
-
+
m_extManager.addExtension( new Extensions() );
}
}
</source>
-
+
</s2>
-
+
<s2 title="Use the new component interface">
-
+
<p>
To use the new SecurityManageable lifecycle extension, we simply
implement
SecurityManageable just as we do with any other Avalon lifecycle
interfaces
(assuming a predefined Component interface
<code>ExtendedComponent</code>).
</p>
-
+
<source>
/**
* ExtendedComponentImpl, demonstrating the use of a custom
@@ -528,9 +528,9 @@
throws SecurityException
{
getLogger().info( "Received SecurityManager instance: " + manager
);
-
+
final String[] files = { "/tmp", "/vmlinuz", "/usr/lib/libc.a" };
-
+
for ( int i = 0; i < files.length; ++i )
{
try
@@ -545,22 +545,22 @@
}
}
}
- </source>
+ </source>
</s2>
-
+
<p>
As you can see, it's a straightforward process to implement a new
extension.
</p>
</s1>
- <s1 title="Need more information ?">
+ <s1 title="Need more information ?">
<p>
If you have any particular questions, comments, etc, please send an
email to the Avalon
developer mailing <link
href="mailto:[email protected]";>list</link>.
</p>
</s1>
-
+
</body>
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