Re: [xwiki-devs] [Proposal] Components Annotations

26 Mar 2009

      On Thu, Mar 26, 2009 at 11:56, Vincent Massol <[email protected]> wrote:
...
Hi,
To start with I propose to model against the plexus annotations but
more simple:
* Component
* Requirement
* Configuration
/**
 * Marks a class as a XWiki component.
 */
@Documented
@Retention(RUNTIME)
@Target(TYPE)
@Inherited
public @interface Component
{
    Class<?> role();
    String hint() default "";
    String instantiationStrategy() default "";
}
/**
 * Configures a requirement.
 */
@Documented
@Retention(RUNTIME)
@Target({ FIELD, METHOD })
@Inherited
public @interface Requirement
{
    Class<?> role() default Object.class;
    String hint() default "";
    //
    // HACK: This is here to support component requirement lists,
which can take a list of hints
    //
    String[] hints() default {};
}
Note: not sure yet why plexus says it's a hack.
/**
 * Marks a field as a configuration element with a default value.
 */
@Documented
@Retention(RUNTIME)
@Target(FIELD)
@Inherited
public @interface Configuration
{
    String name() default "";
    String value();
}
So for example in the code you'd have:
@Component(role=Parser.class)
public class WikiModelXWikiParser implements Parser...
{
      @Requirement
      private LinkParser linkParser;
....
wdyt?
Sounds good but I would suggest maybe another way to see it: having an
annotation for each thing. Then it's possible to put the
@ComponentRole annotation on the interface.

That way it's easier to write a component and harder to forget to
register it, it would be a component simply by implementing a
component interface like in:

@ComponentRole(Parser.class)
public interface Parser
{

}

public class DefaultParser implements Parser
{
      @Requirement
      private LinkParser linkParser;
}

And it is still possible to have a role which is not an interface or
overwrite the role by putting a different @ComponentRole on the
implementation or in a child interface.

And eventually add a way to avoid a class implementing a component
interface to be registered as component (even it's a rare use case I
think)

@ComponentSkip
public class ParserButNotAComponent implements Parser
{

}
...
I'm still researching.
Thanks
-Vincent
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Thomas Mortagne