<div dir="ltr"><br>Hi Nigel!<div><br></div><div>Glad to hear from you. Was wondering, is there a way to manually register listeners? It would be great if this could be leveraged in a CDI SE environment as well as EE environment.</div><div><br></div><div>John</div><div><br><div class="gmail_quote"><div dir="ltr">On Mon, Aug 24, 2015 at 3:48 PM Nigel Deakin <<a href="mailto:nigel.deakin@oracle.com">nigel.deakin@oracle.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
On 24/08/2015 18:42, Antonio Goncalves wrote:<br>
<blockquote type="cite">
<div dir="ltr">Nigel, what do you mean by :
<div><br>
</div>
<div>"The application must obtain an instance of the JMS
listener bean using dependency injection"</div>
<div><br>
</div>
<div>In your examples, it looks like a CDI bean cannot start
listening if not injected : </div>
<div><br>
</div>
<div>
<div><font face="monospace, monospace">@WebServlet("/myjmsservlet1")</font></div>
<div><font face="monospace, monospace"> public class
MyJMSServlet1 extends HttpServlet {</font></div>
<div><font face="monospace, monospace"> </font></div>
<div><font face="monospace, monospace"> <b>@Inject
MyDepScopeListenerBean</b> myDepScopeListenerBean;</font></div>
<div><font face="monospace, monospace"> </font></div>
<div><font face="monospace, monospace"> public void
service(ServletRequest req, ServletResponse res) throws
IOException, ServletException {</font></div>
<div><font face="monospace, monospace"> ...</font></div>
<div><font face="monospace, monospace"> }</font></div>
<div><font face="monospace, monospace"> }</font></div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>Did I understand well ? Is this the case ? Just like a MDB,
I would like a CDI bean to start listening to a message
without being injected, as soon as the application starts. </div>
</div>
</blockquote>
<br></div><div bgcolor="#FFFFFF" text="#000000">
My starting point is that these are normal CDI beans which are
created just like any other CDI bean. The bean's postCreate
behaviour (inserted by the extension) would connect to the JMS
provider and start listening for messages. The bean's preDestroy
behaviour would stop listening for messages and disconnect from the
JMS provider. <br>
<br>
As I understand it, if you want to create a CDI managed bean (so
that it is managed by CDI) then you have to inject it into some code
somewhere. <br>
<br>
Additionally, if the bean is normal scoped, you have to trigger lazy
instantiation by calling a method on the injected bean proxy (e.g.
toString()). <br></div><div bgcolor="#FFFFFF" text="#000000">
<br>
<blockquote type="cite">
<div dir="ltr">
<div>Something like : </div>
<div><br>
</div>
<div>
<div><font face="monospace, monospace"><b>@ApplicationScoped</b></font></div>
<div><font face="monospace, monospace">public class
MyListenerBean{</font></div>
<div><font face="monospace, monospace"> </font></div>
<div><font face="monospace, monospace">
@JMSListener(lookup="java:global/java:global/Trades",type=JMSListener.Type.TOPIC
)</font></div>
<div><font face="monospace, monospace"> public void
deliver(Message message) {</font></div>
<div><font face="monospace, monospace"> ...</font></div>
<div><font face="monospace, monospace"> }</font></div>
<div><font face="monospace, monospace">}</font></div>
</div>
<div><br>
</div>
</div>
</blockquote>
<br></div><div bgcolor="#FFFFFF" text="#000000">
If I understand things correctly, if this is a normal CDI bean then
this alone is not sufficient to cause an instance of the bean to be
created. <br>
<br>
You also need to <br>
(1) inject it into some other bean <br>
(2) create that other bean and<br>
(3) call a method on the <font face="monospace, monospace">MyListenerBean
</font>to trigger lazy initialisation.<br>
<br>
I'm trying to avoid getting ahead of myself here. My current
proposals simply apply to normal CDI managed beans created in the
normal way (via injection and lazy initialisation). But I could
certainly see a benefit in extending this to allow JMS listener
beans to be created in other ways. In particular:<br>
<br>
(a) Creating the bean instance as soon as the bean into which it is
injected enters a new scope rather than waiting for the application
to call a method on it (so-called eager initialisation). That sounds
relatively straightforward to me; this could either be a new
standard CDI feature available to all normal-scoped beans, or
something specific to beans annotated with @JMSListener.<br>
<br>
(b) Creating the bean instance without the need to inject it
anywhere. As you suggest, in the case of ApplicationScoped beans
this would make JMS listener beans more like MDBs. But it might be
equally useful to support this for other normal scopes. For example,
could we annotate a @RequestScoped bean so that every time a new
request scope started, an instance of the bean for that scope was
automatically created? <br></div><div bgcolor="#FFFFFF" text="#000000">
<br>
<blockquote type="cite">
<div dir="ltr">
<div>Or if we manage to get the <font face="monospace,
monospace">@Startup</font> annotation to Commons Annotation
: </div>
<div><br>
</div>
<div>
<div>
<div><font face="monospace, monospace"><b>@Startup</b></font></div>
<div><font face="monospace, monospace">public class
MyListenerBean{</font></div>
<div><font face="monospace, monospace"> </font></div>
<div><font face="monospace, monospace">
@JMSListener(lookup="java:global/java:global/Trades",type=JMSListener.Type.TOPIC
)</font></div>
<div><font face="monospace, monospace"> public void
deliver(Message message) {</font></div>
<div><font face="monospace, monospace"> ...</font></div>
<div><font face="monospace, monospace"> }</font></div>
<div><font face="monospace, monospace">}</font></div>
</div>
</div>
<div><font face="monospace, monospace"><br>
</font></div>
</div>
</blockquote>
<br></div><div bgcolor="#FFFFFF" text="#000000">
That looks as if it's tied to ApplicationScoped. I'd rather look for
something more general.<br>
<br>
Thanks for your comments so far. You're raising issues I have been
thinking about for some time.</div><div bgcolor="#FFFFFF" text="#000000"><br>
<br>
Nigel</div><div bgcolor="#FFFFFF" text="#000000"><br>
<br>
<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div><font face="monospace, monospace"><br>
</font></div>
<div><font face="arial, helvetica, sans-serif">Just thinking
here</font></div>
<div><font face="arial, helvetica, sans-serif"><br>
</font></div>
<div><font face="arial, helvetica, sans-serif">Antonio</font></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Aug 24, 2015 at 6:30 PM, Nigel
Deakin <span dir="ltr"><<a href="mailto:nigel.deakin@oracle.com" target="_blank" onclick="window.open('https://mail.google.com/mail/?view=cm&tf=1&to=nigel.deakin@oracle.com&cc=&bcc=&su=&body=','_blank');return false;">nigel.deakin@oracle.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Over in
the JMS 2.1 expert group I've just published some proposals
to allow any CDI managed bean in a Java EE<br>
application to listen for JMS messages. This would be
implemented as a standard CDI portable extension and would
become<br>
a mandatory part of a full Java EE 8 application server.<br>
<br>
I would welcome any comments from the CDI spec experts here.
If you're interested in helping, please take a look at<br>
<a href="https://java.net/projects/jms-spec/pages/CDIBeansAsJMSListeners" rel="noreferrer" target="_blank">https://java.net/projects/jms-spec/pages/CDIBeansAsJMSListeners</a><br>
and send comments or questions to me or to the public <a href="mailto:users@jms-spec.java.net" target="_blank" onclick="window.open('https://mail.google.com/mail/?view=cm&tf=1&to=users@jms-spec.java.net&cc=&bcc=&su=&body=','_blank');return false;"></a><a href="mailto:users@jms-spec.java.net" target="_blank" onclick="window.open('https://mail.google.com/mail/?view=cm&tf=1&to=users@jms-spec.java.net&cc=&bcc=&su=&body=','_blank');return false;">users@jms-spec.java.net</a>
alias.<br>
<br>
Thanks,<br>
<br>
Nigel<br>
JMS 2.1 specification lead<br>
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</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div>
<div dir="ltr">Antonio Goncalves <br>
Software architect, Java Champion and Pluralsight author<br>
<br>
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