<?xml version="1.0"?>
<document>
<header>
<title>Avalon And EJB Components</title>
<subtitle>Using Avalon Components Inside Of EJB Components</subtitle>
<authors>
<person name="Avalon Documentation Team" email="avalon-
[EMAIL PROTECTED]"/>
</authors>
</header>
<body>
<s1 title="Introduction">
<p>
Avalon is a component framework, as EJB.
There are lot of discussion about pro and cons
of each framework.
The following document tries show some
way using both frameworks, benefiting
for their strength.
</p>
<p>
Today there is quite some common sense about designing EJB.
You should design EJB in a coarse grained fashion.
Speaking in other words EJBs are designed to implement
use cases, or business artifact.
</p>
<p>
In contrast Avalon components could be designed a bit
more fine-grained. Avalon components will be the toolbox
reused across EJB projects.
</p>
<p>
Moreover using Avalon components will give you the chance
to reuse Avalon components in some other J2EE container, e.g.
Servlet Container, or in some stand alone application.
</p>
<p>
As Avalon components are not tied to an EJB container you are
able to do JUnit testing of the Avalon components independently
from the EJBs.
</p>
<p>
Thus it might be possible to reuse the JUnit test in a JMX
environment to provide some continuse testing.
</p>
</s1>
<s1 title="Avalon EJB Frame">
<p>
valon components should not be too visible i
would suggest to use some delegate approach. As it was
suggested by Peter and the AvalonEJBFrame.
</p>
<p>
As side note this approach is not new and it was already
used in the ExaliburTestCase which ties together the
JUnit framwork and tha Avalon framework.
</p>
</s1>
<s1 title="Configuring the Avalon EJB Delegation">
<p>
Using the Avalon framework usually requires some
kind of configuration.
The following sections presents some EJB conformant
configuration options.
</p>
<s2 title="Using ejb-jar.xml">
<p>
You might consider defining the avalon configuration in the ejb-jar.xml.
The ejb-jar.xml describes the characteristics of an EJB.
</p>
<p>
... the ejb-jar.xml snippet ...
</p>
<source><![CDATA[
...
<env-entry>
<env-entry-name>AvalonEJBFrame</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value><![CDATA[
<configuration>
<logger>
<!-- use the log4j logger -->
<log4logger/>
<!-- use the jdk14logger
<jdk14logger/>
-->
<!-- optionally you may use the logkit logger
see ExcaliburTestCase, and avalon.excalibur.logger
<logkit>
<factories>...</factories>
<targets>...</targets>
<categories>...</categories>
</logkit>
-->
</logger>
<components>
<component role="A.ROLE" class="x.y.z.AImpl1"/>
</components>
<configuration>
]]>
<env-entry-value>
</env-entry>
....
]]></source>
<p>
Accessing this configuration:
</p>
<source>
Context ctx = new InitialContext();
String xconfString = ctx.lookup( "java:comp/env/AvalonEJBFrame" );
Configuration xconf = ... // build configuration from xconfString
</source>
Note: prefix java:comp/env is part of the EJB spec and should be
portable across the different application servers.
</s2>
<s2 title="JNDI Lookup of Configuration">
<p>
Lookup the avalon configuration from the JNDI stored as DOM, or plain
xml.
Using this configuration option you must define only a place holder
in the ejb-jar.xml defining where the configuration is has to be looked
up
in the JNDI tree.
</p>
<p>
... the ejb-jar.xml snippet ...
</p>
<source><![CDATA[
...
<env-entry>
<env-entry-name>AvalonEJBFrame</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>avalon/xconf/a/b/c/EJB1.xconf</env-entry-value>
</env-entry>
....
]]></source>
</s2>
<s2 title="JNDI Lookup of AvalonEJBFrame">
<p>
You might consider another option looking up an
AvalonEJBFrame object from the JNDI.
</p>
<p>
... the ejb-jar.xml snippet ...
</p>
<source><![CDATA[
<env-entry>
<env-entry-name>AvalonEJBFrame</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>avalon/xconf/a/b/c/AvalonEJBFrame</env-entry-value>
</env-entry>
....
]]></source>
</s2>
</s1>
<s1 title="Using the AvalonEJBFrame">
<s2 title="Using in a StatelessSessionBean">
<p>
The AvalonEJBFrame object is shared by all StatelessSessionBean
instances.
This means that all avalon components should be ThreadSafe.
</p>
</s2>
<s2 title="Using in a StatefulSessionBean">
<p>
Each StatefulSessionBean instance has its own AvalonEJBFrame.
</p>
</s2>
<s2 title="Using in a EntityBean">
<p>
Each EntityBean instance has its own AvalonEJBFrame.
</p>
</s2>
</s1>
</body>
</document>
Huber Bernhard, email: [EMAIL PROTECTED], homepage:
members.a1.net/berni_huber/index.html
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