this is nice.
what i do like about it
* you can inject anything anywhere
what i dont like is
* post constructor injection like youve mentioned - delegate or not it still
sucks, a different pointcut is needed
* you have to keep your variables transient - very easy mistake to make,
otherwise big boo boo might happen if the dependency is serializable and you
wont know until much later
* you have to inject everything - ie i cant take an instance of injected
service and pass it to some other component to use
* i dont like @Configure on the entire object, i like per-field annotations
on the fields
* you have to have access to the java runtime args to install the weaver
what is needed to fix this
* a different aspect that wraps the bean in the wicket-proxy just like we do
now - that should give you the ultimate freedom, but then what worries me is
if tomcat will let you cluster objects loaded through aspectj classloader.
-Igor
Leszek Gawron-2 wrote:
>
> Hello,
> I just wanted to share another way of injecting spring services into
> wicket code. This one uses AOP.
>
> - o - Why another approach? - o -
>
> Using wicket-spring along with wicket-spring-annot works nicely for
> components (althought you have to remember not initializing it yourself)
> but does not work for other parts of application - models. Just ask your
> self how many times you have put a spring service into wicket page only
> to pass it to model constructed:
>
>> public class RankingPanel extends Panel {
>> @SpringBean
>> private LeagueService leagueService;
>>
>> public RankingPanel( String id, IModel leagueModel ) {
>> super( id );
>> add( new ListView( "ranking", new RankingModel( leagueService,
>> leagueModel ) ) {
>> @Override
>> protected void populateItem( ListItem listItem ) {
>> PlayerRank rank = (PlayerRank) listItem.getModelObject();
>> listItem.add( new Label( "position", String.valueOf(
>> rank.getPosition() ) ) );
>> listItem.add( new Label( "player",
>> rank.getPlayer().getFullName() ) );
>> }
>> } );
>> }
>> }
>
> If you could have your model injected with appropriate service this
> would probably be:
>
>> public class RankingPanel extends Panel {
>> public RankingPanel( String id, IModel leagueModel ) {
>> super( id );
>> add( new ListView( "ranking", new RankingModel( leagueModel ) ) {
>> @Override
>> protected void populateItem( ListItem listItem ) {
>> PlayerRank rank = (PlayerRank) listItem.getModelObject();
>> listItem.add( new Label( "position", String.valueOf(
>> rank.getPosition() ) ) );
>> listItem.add( new Label( "player",
>> rank.getPlayer().getFullName() ) );
>> }
>> } );
>> }
>> }
>
> - o - What you'll need - o -
>
> - your current fancy project
> - one fresh spring (at least 2.0 M1). I have used 2.0-rc2.
> - one ripe aspectj (http://ibiblio.org/maven2/aspectj/) especially
> aspectjrt and aspectjweaver. I have used 1.5.2.
> - java 1.5 (there are probably some ways to do it with 1.4 - didn't
> bother to try)
>
> - o - Implementation - o -
>
> Spring 2.0 M1 introduced @Configurable annotation [1]. We can use it to
> inject spring beans into ANY object (not only created by spring but also
> simply instantiated with new MyObject() ).
>
> Let's create a simple spring context:
>
>> <?xml version="1.0" encoding="UTF-8"?>
>> <beans xmlns="http://www.springframework.org/schema/beans";
>> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
>> xmlns:aop="http://www.springframework.org/schema/aop";
>> xmlns:tx="http://www.springframework.org/schema/tx";
>> xsi:schemaLocation="
>> http://www.springframework.org/schema/beans
>> http://www.springframework.org/schema/beans/spring-beans.xsd
>> http://www.springframework.org/schema/tx
>> http://www.springframework.org/schema/tx/spring-tx.xsd
>> http://www.springframework.org/schema/aop
>> http://www.springframework.org/schema/aop/spring-aop.xsd";>
>> <bean
>> class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>
>>
>> <aop:spring-configured/>
>>
>> <bean id="leagueService"
>> class="com.mobilebox.squasher.service.impl.LeagueServiceImpl
>> autowire="byName"/>
>> </beans>
>
> We have a single service declared here. What's more important is
> <aop:spring-configured/> which simply saying turns on Spring AspectJ
> machinery. Please refer to [1] for additional info.
>
> Now let's build a wicket model:
>
>> @Configurable(autowire = Autowire.BY_NAME, dependencyCheck = true)
>> public class RankingModel extends LoadableDetachableModel {
>> protected transient LeagueService leagueService;
>>
>> public void setLeagueService( LeagueService leagueService ) {
>> this.leagueService = leagueService;
>> }
>>
>> public RankingModel( IModel master ) {
>> this.master = master;
>> }
>>
>> @SuppressWarnings("unchecked")
>> @Override
>> protected Object load() {
>> return new LinkedList( leagueService.getRanking(
>> leagueService.loadRound( (Long) master.getObject( null ) ) ) );
>> }
>> }
>
> Nothing shocking. Just remember to annotate your class with
> @Configurable and make your reference to LeagueService transient.
>
> You need to put an additional file on the classpath to make it all work.
> The location should be META-INF/aop.xml. Mine states:
>
>> <aspectj>
>> <weaver options="-showWeaveInfo
>> -XmessageHandlerClass:org.springframework.aop.aspectj.AspectJWeaverMessageHandler">
>> <include within="com.mobilebox.squasher..*"/>
>> </weaver>
>> <aspects>
>> <include
>> within="org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect"/>
>> </aspects>
>> </aspectj>
>
> You can drop aspectj/weaver/@options. This is only for debugging
> purposes. Remember to change aspectj/weaver/include/@within attribute to
> match the package (and subpackages) you want weaved.
>
> That's all for coding. Let's run it.
>
> - o - Running - o -
>
> Put aspectjrt.jar on classpath. Create you JVM with additional option
> (adjust aspectjweaver location):
>
>> java -javaagent:lib/aspectjweaver.jar
>> com.mobilebox.squasher.launcher.JettyRunner
>
> If you run your container from withing Eclipse IDE put
> '-javaagent:lib/aspectjweaver.jar' in 'VM arguments' editbox.
>
> That's all. AspectJ will weave your RankingModel class on load and
> inject leagueService reference. In case of my project that was starting
> in 5.5 seconds it added 2 more seconds. You can skip Load-Time Weaving
> (LTW) if you just used aspectj compiler or weaved your classes offline.
>
> - o - Serialization - o -
>
> Exactly. Wicket is know with it's I-serialize-everything-like-crazy.
> Turns out this is already handled. You need to make references to your
> services *transient* so they are not serialized. Fortunately when
> deserializing and object from stream AOP also kicks in so you have your
> service reference reinjected. Pure fun!
>
> - o - Gotchas - o -
> Every programming solutions got one. This one also. With current
> @Configurable implementation services get injected AFTER the injectee is
> created (after all constructors got invoked). That means this won't work:
>
>> public class LeaguePage extends BaseSquasherPage {
>> private LeagueService leagueService;
>>
>> public LeaguePage( PageParameters parameters ) throws
>> StringValueConversionException {
>> Long leagueId = parameters.getLong( "id" );
>>
>> // nasty NPE here!
>> League league = leagueService.loadLeague( leagueId );
>>
>> add( new Label( "leagueName", league.getName() ) );
>> }
>> }
>
> You can do 2 things:
> - implement another AOP pointcut so services get injected before
> construction (do not know if that is possible, will dig further)
> - be smarter than AOP itself:
>
>> @Configurable(autowire = Autowire.BY_NAME, dependencyCheck = true)
>> public class LeagueServiceDelegate implements Serializable, LeagueService
>> {
>> private transient LeagueService leagueService;
>>
>> public void setLeagueService( LeagueService leagueService ) {
>> this.leagueService = leagueService;
>> }
>>
>> public League loadLeague( Long id ) {
>> return leagueService.loadLeague( id );
>> }
>> }
>
>> public class LeaguePage extends BaseSquasherPage {
>> private LeagueServiceDelegate leagueService = new
>> LeagueServiceDelegate();
>>
>> public LeaguePage( PageParameters parameters ) throws
>> StringValueConversionException {
>> Long leagueId = parameters.getLong( "id" );
>>
>> // the delegate is already up and running
>> League league = leagueService.loadLeague( leagueId );
>>
>> add( new Label( "leagueName", league.getName() ) );
>> }
>> }
>
> With eclipse you can create such delegate in 30 seconds no matter how
> big the target service is. (generate setter, generate delegates).
>
> - o - Post scriptum - o -
>
> If anyone is interested I will blogify this entry along with sample
> working project to test. Just let me know.
>
> [1]
> http://www.springframework.org/docs/reference/aop.html#aop-atconfigurable
>
> --
> Leszek Gawron
>
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