Java.io.NotSerializableException exception in session beans

Question

Hey experts,
I have written the following code to call a session bean method from a portal application.
               Object obj1 = context.lookup("applications/knet");
               UserInfoHome userInfoHome =
                                   (UserInfoHome) javax.rmi.PortableRemoteObject.narrow(
                                   obj1,
                                   UserInfoHome.class);
               UserInfo userInfo = userInfoHome.create();
               Collection col =
                              userInfo.getAllrooms();
               out.println("The size is  " + col.size() + "<br>");
The following is the implementation of the getAllrooms() method in the session bean
     public Collection getAllrooms() {
          Collection col = null;
          try {
               InitialContext ctx = new InitialContext();
               roomsHome = (RoomsLocalHome) ctx.lookup("java:comp/env/ejb/RoomsBean");
               col = roomsHome.findAllRooms();
          } catch (NamingException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
          } catch (FinderException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
          return col;
In the entity bean the following EJB QL has been used
<EJB QL>
    select object(r) from Rooms r
</<EJB QL>>
I get the following error
com.sap.engine.services.rmi_p4.exception.P4BaseRuntimeException: I/O operation failed : java.io.NotSerializableException: com.sap.engine.services.ejb.entity.finder.EJBLocalCollection :
        at com.sap.engine.services.rmi_p4.server.P4ObjectBrokerServerImpl.getException(P4ObjectBrokerServerImpl.java:926)
        at com.sap.engine.services.rmi_p4.reflect.LocalInvocationHandler.replicateReturnValue(LocalInvocationHandler.java:115)
        at com.sap.engine.services.rmi_p4.reflect.LocalInvocationHandler.invokeInternal(LocalInvocationHandler.java:90)
        at com.sap.engine.services.rmi_p4.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:50)
        at $Proxy180.getAllrooms(Unknown Source)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:324)
        at com.sap.engine.services.ejb.session.stateless_sp5.ObjectStubProxyImpl.invoke(ObjectStubProxyImpl.java:187)
        at $Proxy181.getAllrooms(Unknown Source)
        at com.watercorp.BMS.test.EJBTest.doContent(EJBTest.java:120)
        at com.sapportals.portal.prt.component.AbstractPortalComponent.serviceDeprecated(AbstractPortalComponent.java:209)
        at com.sapportals.portal.prt.component.AbstractPortalComponent.service(AbstractPortalComponent.java:114)
        at com.sapportals.portal.prt.core.PortalRequestManager.callPortalComponent(PortalRequestManager.java:328)
        ... 29 more
Caused by: java.io.NotSerializableException: com.sap.engine.services.ejb.entity.finder.EJBLocalCollection
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1054)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:278)
        at com.sap.engine.services.rmi_p4.reflect.LocalInvocationHandler.replicateReturnValue(LocalInvocationHandler.java:110)
        ... 42 more
Please help

Answer 1

Hi Sabbir,
You are trying to expose a Collection of Entity local interfaces (RoomsLocal) that is the result of RoomsLocalHome.findAllRooms(), through the Session bean's remote interface method getAllrooms(). This is forbidden by the EJB specification and of course cannot work. You have to use remote interfaces of Entity beans when you want to expose them to remote clients - although this is not a good practice either since Entity beans are fine-grained components. Data transfer objects (<a href="http://en.wikipedia.org/wiki/Data_Transfer_Object">DTO</a>) with Session facades should be used for this purpose (you already have a Session facade - the UserInfo bean).
Hope this clarifies it!
-Vladimir
Message was edited by:
        Vladimir Pavlov