THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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The start method needs to look for a Log Service, and register a service listener to track it. If a log service is available, it logs a message.
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public void start() {
// When starting, look for an LogService
ref = context.getServiceReference(LogService.class.getName());
if(ref != null) {
log = (LogService) context.getService(ref);
// Log a starting message
log.log(level,"The component instance " + manager.getInstanceName() + " is starting");
}
// Registered a service listenner
try {
context.addServiceListener(this,"(OBJECTCLASS="+LogService.class.getName()+")");
} catch (InvalidSyntaxException e) { e.printStackTrace(); }
}
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public void stateChanged(int state) {
// log the state changed events
if(log != null) {
if(state == InstanceManager.VALID) { log.log(level, "The component
instance " + manager.getInstanceName() + " becomes valid"); }
if(state == InstanceManager.INVALID) { log.log(level, "The component
instance " + manager.getInstanceName() + " becomes invalid"); }
}
}
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Implementation of the Service Listener interface
To track the availability of the Log Service, the start method has registered the handler as a service listener. So, the handler class needs to implement the Service Listener interface. This interface contains a method called when a service appears, disappears or is modified. The start method has registered a service listener with a filter. So the handler will received only service events matching the filter. (In our case, only service events referring to a Log Service).
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public void serviceChanged(ServiceEvent event) {
// Check if the service event does not infers with the log service
if(ref == null && event.getType() == ServiceEvent.REGISTERED) {
ref = event.getServiceReference();
log = (LogService) context.getService(ref);
// ask the component manager to check the component instance state
manager.checkInstanceState();
}
if(ref != null && event.getType() == ServiceEvent.UNREGISTERING
&& ref == event.getServiceReference()) {
//The log service goes away
log = null;
context.ungetService(ref);
ref = context.getServiceReference(LogService.class.getName());
if(ref != null) { log = (LogService) context.getService(ref); }
else { manager.checkInstanceState(); }
}
}
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Note: the file path need to used
two '\' instead of one '\'
Conclusion
In this document, we present how-to develop handler for you components. We describe two small examples : a log handler and a properties handler. See the handler proposition section of the iPOJO documentation to see available handlers or to propose your own handler.