Category: Component
Status: Closed

Severity: HIGH
Reported against release: 0.8
Fixed in release: 0.8.1 (Beta Refresh)

PROBLEM:

The developer who reported this defect actually has a service object 
that itself attempts to provide a service once it is downloaded into a 
client program. When he calls Component.distributeObject(), null is 
returned, and he gets an exception when he passes null to 
Component.provideService().

Here is the stack trace:

FriendlyDbPluginImpl Exception = 
net.openwings.component.InvalidServiceException: Service Object does 
not implement service interface.
net.openwings.component.InvalidServiceException: Service Object does 
not implement service interface.
        at 
com.mot.openwings.component.jini.JiniComponent.provideServiceCheck
(JiniComponent.java:666)
        at com.mot.openwings.component.jini.JiniComponent.provideService
(JiniComponent.java:254)
        at com.mot.dcgs.friendly.dbplugin.FriendlyDbPluginImpl.init
(FriendlyDbPluginImpl.java:64)
        at com.mot.c4i.dbpluginctrl.DbPluginTree.addPlugin
(DbPluginTree.java:221)
        at com.mot.c4i.dbpluginctrl.DbPluginTree.serviceProvided
(DbPluginTree.java:129)
        at 
com.mot.openwings.component.jini.UseServiceManager$LookupCacheHolder.ser
viceAdded(UseServiceManager.java:1009)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl.serviceNotifyDo
(ServiceDiscoveryManager.java:1156)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl.addServiceNotify
(ServiceDiscoveryManager.java:1122)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl.addService
(ServiceDiscoveryManager.java:1061)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl.access$8
(ServiceDiscoveryManager.java:1051)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl$NotifyEventTask.
exec(ServiceDiscoveryManager.java:546)
        at 
net.jini.lookup.ServiceDiscoveryManager$LookupCacheImpl.execTasks
(ServiceDiscoveryManager.java:987)
        at net.jini.lookup.ServiceDiscoveryManager$TaskThread.run
(ServiceDiscoveryManager.java:330)

ANALYSIS:

ComponentServices implements Component.distributeObject() by using the 
ConnectorLoader to load a connector, and then doing some setup on the 
connector (connecting the provider proxy, etc.).

The ConnectorLoader class attempts to load connectors by loading the 
connector class and instantiating it. However, it only attempts to load 
the class by doing a "Class.forName()". This only checks the class 
loader of the calling class, which is the ConnectorLoader class itself. 

In most situations, this approach works, since the application, 
Component Services, and the ConnectorLoader are all loaded by the same 
class loader. This defect uncovers a situation where the 
ConnectorLoader is loaded by the main application class loader, and the 
connector interface (and in fact the actual connector as well) are in a 
URLClassLoader. 

The fix is to make the ConnectorLoader do more extensive checking. It 
should try two additional different class loaders when searching for 
connector classes:
1. The context class loader.
2. The class loader that loaded the connector interface.

WORKAROUND:

The jar file for the container could be added to the classpath of the 
program using the service. Note that this is definitely not a long-term 
solution.

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