Actually it's a problem if @SpringBean annotation creates new objects of
class that is supposed to be a *singleton*.
Is it really impossible to create a proxy class without creating a new
object of delegatee ?
Here is a discussion we had about it:
[23:10] <Smike> I just noticed that @SpringBean creates a new instance
of my Spring bean
[23:10] <Smike> it's not good, after all Spring pojos are supposed to be
singletons
[23:11] <Hali_303> Smike: it should not create a new instance if the
Spring bean is a singleton
[23:12] <Smike> it does
[23:12] <Hali_303> Smike: not all Spring beans are singletons, far from
it. Spring has many scopes, singleton scope is just one out of many scopes
[23:12] <Smike> it's default, isnt it ?
[23:12] <Hali_303> yes
[23:13] <Hali_303> how do you know that it's creating multiple instances?
[23:13] <Smike> my beans have default scope
[23:14] <Smike> breakpoints in constructor and logging statements
[23:14] <Smike> and I have seen the same issue discussed in mail list
[23:14] <Smike> where Igor says cglib needs to create a new object
[23:15] <Smike> so every bean needs a default constructor
[23:15] <Hali_303> could you give me a pointer to this discussion?
[23:16] <Smike> here is the title [Wicket-user] Wicket requiring one of
my Spring managed beans to have a default constructor
[23:18] <Smike> it should only lookup a bean from spring context, why
it needs to create a new object... I have no idea
[23:18] <Hali_303> Smike: yeah I think what Igor says is right
[23:19] <Smike> why it can't use existing object ?
[23:19] * srufle ([EMAIL PROTECTED]) Quit ( Read
error: 110 (Connection timed out) )
[23:19] * srufle_______ is now known as srufle
[23:19] <Hali_303> Smike: regarding jdk proxies vs cglib
[23:19] <Hali_303> Smike: yeah exactly, I don't really see the
connection between that thread and your problem
[23:20] <Hali_303> the guy in that thread did not complain about
multiple instances of singleton beans
[23:20] <Smike> the problem is that @SpringBean creates a new class
[23:20] <Smike> and that thread only confirms that
[23:21] <Hali_303> it's not SpringBean, its cglib that creates one
[23:21] <Hali_303> and should create it only once, not every time use
inject the bean
[23:21] <Hali_303> and should create it only once, not every time use
inject the bean
[23:21] <Smike> yes, @SpringBean annotation creates a proxy based on cglib
[23:22] <Smike> ok, but I can't believe that there is no way to
create a proxy without creating a new class
[23:23] <Smike> of course, I am not reflection expert
[23:24] <Smike> but I think it's possible
[23:24] <Smike> at least with JDK proxy class
[23:24] <Smike> I have never used cglib though
[23:25] <Smike> so.... I think this is important issue and should be fixed
[23:26] <pertl> Smike: I remember having a similar issue when using a
bean without interface...maybe it's related to your issue... I got
multiple instances of one singleton bean... once I used the interface /
implementation pattern (UserDAO + UserDAOImpl) everything worked...
[23:26] <Smike> yes could be
[23:27] <pertl> Smike: give it a try ... use the interface but let
spring instantiate the implementation class... maybe it works out
[23:28] <Hali_303> I'm using that too, and it works
[23:28] <Hali_303> I've even used prototype beans and that worked too
[23:28] <Smike> sounds good, ok, I'll try
you have to have an empty constructor. afaik it doesnt have to be
public. this is so that cglib can create a proxy, i dont think there
is a way around it.
-igor
On 5/9/07, * Matt Welch* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I am using the @SpringBean annotation to instantiate Spring
dependencies in my wicket pages but I have one page that is giving
me a error that I'm having trouble dealing with. Here's an example.
The Wicket page class:
public class Viewer extends WebPage {
@SpringBean(name = "contentSettings")
private ContentSettings contentSettings;
@SpringBean(name = "learningItemRepository")
private LearningItemRepository learningItemRepository;
public Viewer() {
//add some simple components to the page
}
}
The vast majority of the time, my Spring managed beans are
implementations of interfaces and not standalone concrete classes,
however, in this particular situation I have about a dozen or so
beans that don't need to follow that pattern.
"LearningRepository" is an interface with a concrete
implementation. "ContentSettings" on the other hand is a
standalone concrete class. Both classes are properly setup in my
Spring configuration xml files and I have a suite of unit tests
which load the classes using Spring so I know that they "should"
work. In fact, "LearningRepository" does work fine, but I'm
getting an error from Wicket with regards to the the
ContentSettings class:
---------------------------------------------
java.lang.IllegalArgumentException: Superclass has no null
constructors but no arguments were given
at net.sf.cglib.proxy.Enhancer.emitConstructors (Enhancer.java:718)
at net.sf.cglib.proxy.Enhancer.generateClass(Enhancer.java:499)
at
net.sf.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
at net.sf.cglib.core.AbstractClassGenerator.create
(AbstractClassGenerator.java:216)
at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377)
at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:285)
at org.apache.wicket.proxy.LazyInitProxyFactory.createProxy
(LazyInitProxyFactory.java:138)
at
org.apache.wicket.spring.injection.annot.AnnotProxyFieldValueFactory.getFieldValue(AnnotProxyFieldValueFactory.java:102)
at org.apache.wicket.injection.Injector.inject(Injector.java :109)
at
org.apache.wicket.injection.ConfigurableInjector.inject(ConfigurableInjector.java:40)
at
org.apache.wicket.injection.ComponentInjector.onInstantiation(ComponentInjector.java:54)
at
org.apache.wicket.Application.notifyComponentInstantiationListeners
(Application.java:914)
at org.apache.wicket.Component.<init>(Component.java:606)
at org.apache.wicket.MarkupContainer.<init>(MarkupContainer.java:111)
at org.apache.wicket.Page.<init>( Page.java:195)
at org.apache.wicket.markup.html.WebPage.<init>(WebPage.java:97)
at
com.ptc.fusion.web.pages.FusionBasePage.<init>(FusionBasePage.java:18)
at com.ptc.fusion.web.pages.viewer.Viewer .<init>(Viewer.java:41)
at com.ptc.fusion.web.pages.viewer.Viewer$1.getPage(Viewer.java:79)
at
org.apache.wicket.markup.html.link.PageLink.onClick(PageLink.java:153)
at org.apache.wicket.markup.html.link.Link.onLinkClicked
(Link.java:222)
at java.lang.reflect.Method.invoke(Method.java:585)
at
org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:186)
at
org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents
(ListenerInterfaceRequestTarget.java:73)
at
org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:90)
at org.apache.wicket.RequestCycle.processEventsAndRespond
(RequestCycle.java:962)
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1035)
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1114)
at org.apache.wicket.RequestCycle.request(RequestCycle.java :474)
at
org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:248)
at
org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:122)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter
(ServletHandler.java:1065)
at
org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:173)
at org.springframework.web.filter.OncePerRequestFilter.doFilter
(OncePerRequestFilter.java:77)
at
org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1065)
at
org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:365)
at
org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:185)
at
org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at
org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java
:689)
at
org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:391)
at
org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:146)
at org.mortbay.jetty.handler.HandlerCollection.handle
(HandlerCollection.java:114)
at
org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:285)
at org.mortbay.jetty.HttpConnection.handleRequest
(HttpConnection.java:457)
at
org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:751)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:500)
at org.mortbay.jetty.HttpParser.parseAvailable (HttpParser.java:209)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:357)
at
org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:329)
at org.mortbay.thread.BoundedThreadPool$PoolThread.run
(BoundedThreadPool.java:475)
-----------------------------
Even though ContentSettings isn't mentioned in the stacktrace, I
set a break point at the error location and to and discovered that
it was indeed that class causing me problems. It's true that there
is no default constructor in ContentSettings. In fact, none of my
Spring managed classes have a default constructor due to my using
constructor based injection.
The error goes away if I add an empty constructor or if I convert
the ContentSettings class into a ContentSettings interface and a
ContentSettingsImpl interface. I realize the latter is generally
considered good form, however I may eventually have dozens of
these XxxxxSettings classes are for the most part they are just
wrappers to another class so they really don't benefit all that
much from the Interface/Implementation pattern.
Does anyone know a way around this problem or am I stuck?
-Matt
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