Could not instantiate Seam component error

[lle]

Hi,

I have a conversation scope action class, which has a bijectional conversation-scope object as a DataModelSelection. When I executed an ajax4jsf request (from an a4j:commandLink), I always get the following exception:

org.jboss.seam.InstantiationException: Could not instantiate Seam component: selectedSession
 at org.jboss.seam.Component.newInstance(Component.java:1722)
 at org.jboss.seam.Component.getInstance(Component.java:1625)
 at org.jboss.seam.Component.getInstance(Component.java:1592)
 at org.jboss.seam.jsf.SeamVariableResolver.resolveVariable(SeamVariableResolver.java:46)
 at org.apache.myfaces.trinidadinternal.el.TrinidadVariableResolver.resolveVariable(TrinidadVariableResolver.java:52)
 at com.sun.facelets.el.LegacyELContext$LegacyELResolver.getValue(LegacyELContext.java:134)
 at com.sun.el.parser.AstIdentifier.getValue(AstIdentifier.java:68)
 at com.sun.el.parser.AstValue.getValue(AstValue.java:107)
 at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:192)
 at com.sun.facelets.el.TagValueExpression.getValue(TagValueExpression.java:71)
 at com.sun.facelets.el.LegacyValueBinding.getValue(LegacyValueBinding.java:56)
 at javax.faces.component.UIData.getValue(UIData.java:1023)
 at org.apache.myfaces.component.html.ext.HtmlDataTableHack.createDataModel(HtmlDataTableHack.java:437)
 at org.apache.myfaces.component.html.ext.HtmlDataTable.createDataModel(HtmlDataTable.java:847)
 at org.apache.myfaces.component.html.ext.HtmlDataTableHack.getDataModel(HtmlDataTableHack.java:414)
 at org.apache.myfaces.component.html.ext.HtmlDataTable.getDataModel(HtmlDataTable.java:839)
 at org.apache.myfaces.component.html.ext.HtmlDataTableHack.getRowCount(HtmlDataTableHack.java:87)
 at javax.faces.component.UIData.processColumnChildren(UIData.java:689)
 at javax.faces.component.UIData.processDecodes(UIData.java:585)
 at org.apache.myfaces.component.html.ext.HtmlDataTable.processDecodes(HtmlDataTable.java:293)
 at javax.faces.component.UIComponentBase.processDecodes(UIComponentBase.java:605)
 at javax.faces.component.UIForm.processDecodes(UIForm.java:56)
 at org.ajax4jsf.framework.ajax.AjaxViewRoot.processDecodes(AjaxViewRoot.java:353)
 at org.apache.myfaces.lifecycle.ApplyRequestValuesExecutor.execute(ApplyRequestValuesExecutor.java:32)
 at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:95)
 at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:70)
 at javax.faces.webapp.FacesServlet.service(FacesServlet.java:139)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:147)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.myfaces.trinidadinternal.webapp.TrinidadFilterImpl._invokeDoFilter(TrinidadFilterImpl.java:326)
 at org.apache.myfaces.trinidadinternal.webapp.TrinidadFilterImpl._doFilterImpl(TrinidadFilterImpl.java:290)
 at org.apache.myfaces.trinidadinternal.webapp.TrinidadFilterImpl.doFilter(TrinidadFilterImpl.java:213)
 at org.apache.myfaces.trinidad.webapp.TrinidadFilter.doFilter(TrinidadFilter.java:90)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.ajax4jsf.framework.ajax.xmlfilter.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:75)
 at org.ajax4jsf.framework.ajax.xmlfilter.BaseFilter.doFilter(BaseFilter.java:213)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.jboss.seam.servlet.SeamExceptionFilter.doFilter(SeamExceptionFilter.java:46)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.jboss.seam.servlet.SeamRedirectFilter.doFilter(SeamRedirectFilter.java:32)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
 at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
 at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
 at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
 at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
 at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
 at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.InstantiationException: com.ga.riskapp.session.GASession
 at java.lang.Class.newInstance0(Class.java:335)
 at java.lang.Class.newInstance(Class.java:303)
 at org.jboss.seam.Component.instantiateJavaBean(Component.java:1045)
 at org.jboss.seam.Component.instantiate(Component.java:1008)
 at org.jboss.seam.Component.newInstance(Component.java:1718)
 ... 60 more

Here is the action class code snippet:

@Name("detailsearch")
@Scope(ScopeType.CONVERSATION)
@GALoggedIn
public class GAAccountDetailsAction {

 @In
 private Session gadb;
 @In
 private GAHostAppInfo hostApp;
 @In
 private FacesMessages facesMessages;
 @Logger
 private Log log;
 @DataModel
 private List<GASession> sessionList;
 @DataModelSelection
 @In(required=false) @Out(required=false)
 private GASession selectedSession;

 public void applyScale1() {
 try {
 this.scale = 1;
 getSessions();
 } catch (Throwable t) {
 log.error("Error while applying scale", t);
 facesMessages.addFromResourceBundle(Constants.APPLICATION_ERROR);
 }
 }
...
}

Here is the GASession class:

@Name("selectedSession")
@Scope(ScopeType.CONVERSATION)
public class GASession {
...
}

Anyone knows why such an exception thrown? When I accessed the debug page, I saw the "selectedSession" object existed in the "detailsearch". So, I am not sure why such an exception thrown.
Thanks.

[hstang]

Hi,

Does your GASession class have a default no-arg constructor?

[lle]

No, it doesn't because my app controls the instantiation of this class with some init values. I don't want Seam to create it. The context variable should point to an existing GASession with @DataModelSelection. Why does Seam need to instantiate this component?

[hstang]

Because somewhere in your code or view, you are referencing "selectedSession" which is a Seam component (you gave it a @Name)

[lle]

Yes, my view does reference the context variable "selectedSession".

1. Since GASession is a Seam component, it will be instantiated by Seam even if the context variable already exists. Is that correct?

2. If I provide a default no-args constructor, this exception will go away? Then, do I have to provide an @Create method to initialize the GASession object created by Seam? This is where I don't understand. If Seam will instantiate a new instance of this component, then will it refers to the correct instance currently selected by @DataModelSelection?

Thanks.

[norman.richards]

This looks very suspicious to me:

 @DataModelSelection
 @In(required=false) @Out(required=false)
 private GASession selectedSession;

Why are you trying to inject it?

[lle]

It's because initially that object is injected from another page. However, I have changed to use page action.
Even if I removed the @In(required=false), the same exception occurs.

I can provide a no-args constructor as suggested by hstang. However I'd like to understand the behavior of Seam to avoid further issues.

Thanks.
ly

[hstang]

If you provide a no-args constructor, the exception dealing with instantiation will be gone. This is the only way Seam can construct your seam components properly. Yes, as you suggested, use the @Create to initialize other important properties pertaining to the class. The annotated method is called once Seam has fully initialize the component.

As for @DataModel, this will outject the annotated property to the scope of the owning component. In your case, the conversation.

And for @DataModelSelection, this will inject the selected model object, if it's successfully look up in the contexts. You have to ensure that the conversation is long-running, just long enough though, so that @DataModelSelection object can be successfully be retrieved through the @DataModel property.