<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 26 oct. 2011, at 15:47, Kevin Pollet wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi,<div><br></div><div><div class="gmail_quote">On 25 October 2011 14:34, Emmanuel Bernard <span dir="ltr"><<a href="mailto:emmanuel@hibernate.org" target="_blank">emmanuel@hibernate.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Your email made me think of a potential solution.<br>
<br>
We could use the service loader pattern to declare a constraint implementor service that would list the bindings between a constraint and its implementation.<br>
<br>
Add in implementation jars<br>
<br>
META-INF/services/javax.validation.ConstraintValidator<br>
<br>
where `javax.validation.ConstraintValidator` contains the list of fully qualified class names of constraint implementations.<br>
<br>
>From the class, we can infer the @Constraint being validated.<br>
<br>
I think this works very well:<br>
<br>
- this list is compiled when ValidatorFactory is built<br>
- this list can be equally built by the compiler and thus the annotation processor has equal knowledge<br>
<br>
The only gotcha I can see is that in modular environments like OSGi and co. They tend to hide such files from the classpath. So discovering the various resources named `META-INF/services/javax.validation.ConstraintValidator` might be flaky.<br>
That's an open subject in any case (ie. making BV run better in modular environments).<br>
<br>
Any one with better knowledge of OSGi or any other modular environment want to shred some lights?<font color="#888888"><br></font></blockquote><div><br></div><div>I'm not an OSGi expert but I've already implemented such mechanism to discover BV implementations, with a custom ValidationProviderResolver, in OSGi. For this test I've used the following design, one bundle for the api and one bundle per implementation (the common use case). </div>
<div><br></div><div>In OSGi, the bundle resources are hidden to others bundle. To get something like that working you need to iterate on all bundles and check if the `META-INF/services/javax.validation.ConstraintValidator` is present with the bundle classloader. The main issue here is to deal with dynamism but that's not the goal :-) One drawback with that approach is that you expose your implementations which tend to be hidden in a modular world.</div></div></div></blockquote><div><br></div><div>That's the thing, it can be hidden from the application bundles but it must be visible from frameworks bundles (whether ootb in the app server or provided in the application.</div><br><blockquote type="cite"><div><div class="gmail_quote">
<div><br></div><div>IMHO, if the mechanism used to discover the ConstraintValidator implementations is pluggable, it should work.</div></div></div></blockquote><div><br></div><div>What do you have in mind? I don't mind having a pluggable discovery mechanism but we need a standard way for a constraint implementor to expose the fact that it implements validators for some constraints.</div></div><br></body></html>