Curator ServiceCacheListener is triggered three times when a service is added - apache-zookeeper

Question

I am learning zookeeper and trying out the Curator framework for service discoveries. However, I am facing a weird issue that I have difficulties to figure out. The problem is when I tried to register an instance via serviceDiscovery, the cacheChanged event of the serviceCache gets triggered three times. When I removed an instance, it is only triggered once, which is the expected behavior. Please see the code below:
public class DiscoveryExample {
private static String PATH = "/base";
static ServiceDiscovery<InstanceDetails> serviceDiscovery = null;
public static void main(String[] args) throws Exception {
CuratorFramework client = null;
try {
// this is the ip address of my VM
client = CuratorFrameworkFactory.newClient("192.168.149.129:2181", new ExponentialBackoffRetry(1000, 3));
client.start();
JsonInstanceSerializer<InstanceDetails> serializer = new JsonInstanceSerializer<InstanceDetails>(
InstanceDetails.class);
serviceDiscovery = ServiceDiscoveryBuilder.builder(InstanceDetails.class)
.client(client)
.basePath(PATH)
.serializer(serializer)
.build();
serviceDiscovery.start();
ServiceCache<InstanceDetails> serviceCache = serviceDiscovery.serviceCacheBuilder()
.name("product")
.build();
serviceCache.addListener(new ServiceCacheListener() {
#Override
public void stateChanged(CuratorFramework curator, ConnectionState state) {
// TODO Auto-generated method stub
System.out.println("State Changed to " + state.name());
}
// THIS IS THE PART GETS TRIGGERED MULTIPLE TIMES
#Override
public void cacheChanged() {
System.out.println("Cached Changed ");
List<ServiceInstance<InstanceDetails>> list = serviceCache.getInstances();
Iterator<ServiceInstance<InstanceDetails>> it = list.iterator();
while(it.hasNext()) {
System.out.println(it.next().getAddress());
}
}
});
serviceCache.start();
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.print("> ");
String line = in.readLine();
} finally {
CloseableUtils.closeQuietly(serviceDiscovery);
CloseableUtils.closeQuietly(client);
}
}
}
AND
public class RegisterApplicationServer {
final static String PATH = "/base";
static ServiceDiscovery<InstanceDetails> serviceDiscovery = null;
public static void main(String[] args) throws Exception {
CuratorFramework client = null;
try {
client = CuratorFrameworkFactory.newClient("192.168.149.129:2181", new ExponentialBackoffRetry(1000, 3));
client.start();
JsonInstanceSerializer<InstanceDetails> serializer = new JsonInstanceSerializer<InstanceDetails>(
InstanceDetails.class);
serviceDiscovery = ServiceDiscoveryBuilder.builder(InstanceDetails.class).client(client).basePath(PATH)
.serializer(serializer).build();
serviceDiscovery.start();
// SOME OTHER CODE THAT TAKES CARES OF USER INPUT...
} finally {
CloseableUtils.closeQuietly(serviceDiscovery);
CloseableUtils.closeQuietly(client);
}
}
private static void addInstance(String[] args, CuratorFramework client, String command,
ServiceDiscovery<InstanceDetails> serviceDiscovery) throws Exception {
// simulate a new instance coming up
// in a real application, this would be a separate process
if (args.length < 2) {
System.err.println("syntax error (expected add <name> <description>): " + command);
return;
}
StringBuilder description = new StringBuilder();
for (int i = 1; i < args.length; ++i) {
if (i > 1) {
description.append(' ');
}
description.append(args[i]);
}
String serviceName = args[0];
ApplicationServer server = new ApplicationServer(client, PATH, serviceName, description.toString());
server.start();
serviceDiscovery.registerService(server.getThisInstance());
System.out.println(serviceName + " added");
}
private static void deleteInstance(String[] args, String command, ServiceDiscovery<InstanceDetails> serviceDiscovery) throws Exception {
// in a real application, this would occur due to normal operation, a
// crash, maintenance, etc.
if (args.length != 2) {
System.err.println("syntax error (expected delete <name>): " + command);
return;
}
final String serviceName = args[0];
Collection<ServiceInstance<InstanceDetails>> set = serviceDiscovery.queryForInstances(serviceName);
Iterator<ServiceInstance<InstanceDetails>> it = set.iterator();
while (it.hasNext()) {
ServiceInstance<InstanceDetails> si = it.next();
if (si.getPayload().getDescription().indexOf(args[1]) != -1) {
serviceDiscovery.unregisterService(si);
}
}
System.out.println("Removed an instance of: " + serviceName);
}
}
I appriciate if anyone can please point out where I am doing wrong and maybe can share some good materials/examples so I can refer to. The official website and the examples on github does not help a lot.