Entry Listener
You can listen to map entry events. Hazelcast distributed map offers the method addEntryListener to add an entry listener to the map.
Let's take a look at the below sample code.
public class Listen {
public static void main( String[] args ) {
HazelcastInstance hz = Hazelcast.newHazelcastInstance();
IMap<String, String> map = hz.getMap( "somemap" );
map.addEntryListener( new MyEntryListener(), true );
System.out.println( "EntryListener registered" );
}
static class MyEntryListener implements EntryListener<String, String> {
@Override
public void entryAdded( EntryEvent<String, String> event ) {
System.out.println( "Entry Added:" + event );
}
@Override
public void entryRemoved( EntryEvent<String, String> event ) {
System.out.println( "Entry Removed:" + event );
}
@Override
public void entryUpdated( EntryEvent<String, String> event ) {
System.out.println( "Entry Updated:" + event );
}
@Override
public void entryEvicted( EntryEvent<String, String> event ) {
System.out.println( "Entry Evicted:" + event );
}
@Override
public void mapEvicted( MapEvent event ) {
System.out.println( "Map Evicted:" + event );
}
@Override
public void mapCleared( MapEvent event ) {
System.out.println( "Map Cleared:" + event );
}
}
}
And, now let's perform some modifications on the map entries using the below sample code.
public class Modify {
public static void main( String[] args ) {
HazelcastInstance hz = Hazelcast.newHazelcastInstance();
IMap<String, String> map = hz.getMap( "somemap");
String key = "" + System.nanoTime();
String value = "1";
map.put( key, value );
map.put( key, "2" );
map.delete( key );
}
}
If you execute the class Listen and then execute Modify, you might get the below output produced by Listen.
entryAdded:EntryEvent {Address[192.168.1.100]:5702} key=251359212222282,
oldValue=null, value=1, event=ADDED, by Member [192.168.1.100]:5702
entryUpdated:EntryEvent {Address[192.168.1.100]:5702} key=251359212222282,
oldValue=1, value=2, event=UPDATED, by Member [192.168.1.100]:5702
entryRemoved:EntryEvent {Address[192.168.1.100]:5702} key=251359212222282,
oldValue=2, value=2, event=REMOVED, by Member [192.168.1.100]:5702
Entry Listener runs on event threads which are also used by other listeners (e.g. collection listeners, pub/sub message listeners, etc.). This means entry listeners can access other partitions. Consider this when you run long tasks, since listening to those tasks may cause other event listeners to starve.