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Thin functional layer on top of RMI.
There is a newer version: 1.2
package remote.server;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.rmi.RemoteException;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;
import java.util.WeakHashMap;

import remote.Remote;

public class DGCClient {
	private final Map> remotes = new HashMap<>();
	private final Map> collected = new HashMap<>();
	private final Map> live = new HashMap<>();
	private final Map>>> caches = new HashMap<>();
	final long value = Long.valueOf(System.getProperty("java.rmi.dgc.leaseValue", "600000"));
	private final Timer timerGc = new Timer(true);
	private final Timer timer = new Timer(true);
	private final RemoteFactory factory;

	DGCClient(final RemoteFactory factory) {
		this.factory = factory;
		timer.schedule(new TimerTask() {
			@Override
			public void run() {
				try {
					gc();
				} catch (final RemoteException e) {
					e.printStackTrace();
				}
			}
		}, 0, value >> 1);
		timerGc.schedule(new TimerTask() {
			@Override
			public void run() {
				System.gc();
			}
		}, 0, Long.valueOf(System.getProperty("sun.rmi.dgc.client.gcInterval", "3600000")));
	}

	Remote cache(final RemoteImpl_Stub obj) {
		Remote o;
		final String id = obj.getId();
		if (!caches.containsKey(id)) {
			caches.put(id, new WeakHashMap<>());
		}
		final Map>> cache = caches.get(id);
		final Reference> w = cache.get(obj);
		if (w == null || (o = w.get()) == null) {
			cache.put(obj, new WeakReference<>(obj));
			dirty(id, obj.getNum());
			obj.setState(true);
			return obj;
		} else {
			return o;
		}
	}

	synchronized void clean(final String id, final long num) {
		collected.get(id).add(num);
		live.get(id).remove(num);
	}

	synchronized void dirty(final String id, final long num) {
		if (!remotes.containsKey(id)) {
			remotes.put(id, factory.dgc(id));
			collected.put(id, new LinkedHashSet<>());
			live.put(id, new LinkedHashSet<>());
		}
		live.get(id).add(num);
	}

	private synchronized String[] getIds() {
		return remotes.keySet().toArray(new String[0]);
	}

	private synchronized Remote getRemote(final String id) {
		return remotes.get(id);
	}

	private synchronized Long[] getCollected(final String id) {
		return collected.get(id).toArray(new Long[0]);
	}

	private synchronized void removeCollected(final String id, final Long nums[]) {
		collected.get(id).removeAll(Arrays.asList(nums));
	}

	private synchronized Long[] getLive(final String id) {
		return live.get(id).toArray(new Long[0]);
	}

	void gc() throws RemoteException {
		final String localId = factory.getId();
		final long duration = value;
		for (final String id : getIds()) {
			final Remote dgc = getRemote(id);
			final Long cs[] = getCollected(id);
			final Long ds[] = getLive(id);
			if (cs.length > 0) {
				dgc.map(a -> a.clean(cs, localId));
			}
			if (ds.length > 0) {
				dgc.map(a -> a.dirty(ds, localId, duration));
			}
			removeCollected(id, cs);
		}
	}
}