java.rmi.dgc

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1. Simple RMI Server with DGC

import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.dgc.*;

public class RMIServer {

    private RMIServerImpl impl;

    public RMIServer() throws RemoteException {
        impl = new RMIServerImpl();
        UnicastRemoteObject.exportObject(impl, 0);
    }

    public static void main(String[] args) {
        try {
            RMIServer server = new RMIServer();
            System.out.println("Server started");
            Runtime.getRuntime().addShutdownHook(new Thread(() -> {
                try {
                    UnicastRemoteObject.unexportObject(server.impl, true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

class RMIServerImpl implements RMIInterface {

    @Override
    public String getMessage() {
        return "Hello from the server";
    }

}

2. Client with DGC Lease Checking

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.dgc.*;

public class RMIClient {

    public static void main(String[] args) {
        try {
            // Lookup the registry
            Registry registry = LocateRegistry.getRegistry();
            // Get the remote object reference
            RMIInterface server = (RMIInterface) registry.lookup("rmiServer");
            // Create a lease checker to monitor the server's lease
            LeaseChecker leaseChecker = new LeaseChecker((RMIServerImpl) server);
            // Start the lease checker thread
            leaseChecker.start();
            // Make a call to the server
            System.out.println(server.getMessage());
            // Wait for a few seconds to allow the lease to expire
            Thread.sleep(6000);
            // Check if the lease has expired
            if (leaseChecker.isExpired()) {
                System.out.println("Lease expired");
            } else {
                System.out.println("Lease still active");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

class LeaseChecker extends Thread {

    private RMIServerImpl server;
    private boolean expired;

    public LeaseChecker(RMIServerImpl server) {
        this.server = server;
    }

    @Override
    public void run() {
        try {
            // Get the server's lease
            Lease lease = server.getLease();
            // Monitor the lease until it expires or is renewed
            while (true) {
                // Check if the lease has expired
                if (lease.expired()) {
                    expired = true;
                    break;
                }
                // Renew the lease if it is close to expiring
                if (lease.getRemainingLeaseTime() < 3000) {
                    lease = server.renewLease();
                }
                // Sleep for a second to reduce CPU usage
                Thread.sleep(1000);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public boolean isExpired() {
        return expired;
    }

}

3. Server with DGC Cleaner

import java.rmi.*;
import java.rmi.server.*;
import java.rmi.dgc.*;
import java.util.*;

public class RMIServerCleaner implements RMICleaner, Remote {

    private Map<Long, Lease> leases = new HashMap<>();

    @Override
    public Lease renewLease(Remote ref, long value, long leaseDuration) throws RemoteException {
        long leaseId = ref.hashCode();
        synchronized (leases) {
            leases.put(leaseId, new Lease(value, leaseDuration));
        }
        return new Lease(value, leaseDuration);
    }

    @Override
    public void clean(long leaseId, long renewId, Remote ref) {
        synchronized (leases) {
            leases.remove(leaseId);
        }
    }

    @Override
    public void unexportObject(Remote ref, boolean force) {
        long leaseId = ref.hashCode();
        synchronized (leases) {
            leases.remove(leaseId);
        }
    }

}

4. Client with Custom Remote Reference

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.dgc.*;
import java.lang.ref.*;

public class RMICustomClient {

    public static void main(String[] args) {
        try {
            // Lookup the registry
            Registry registry = LocateRegistry.getRegistry();
            // Create a custom remote reference
            RMICustomReference reference = new RMICustomReference();
            // Get the remote object reference
            RMIInterface server = (RMIInterface) reference.getRemote(registry, "rmiServer");
            // Make a call to the server
            System.out.println(server.getMessage());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

class RMICustomReference extends WeakReference<Remote> implements RemoteReference {

    private long leaseId;
    private RMIDGCServer server;

    public RMICustomReference() {
        super(null);
    }

    public RMICustomReference(Remote obj, RMIDGCServer server) {
        super(obj);
        this.server = server;
        long leaseId = server.lease(this, 60000, 120000);
        this.leaseId = leaseId;
    }

    @Override
    public Remote getRemote() {
        return super.get();
    }

    @Override
    public long getLeaseId() {
        return leaseId;
    }

    @Override
    public void renewLease(long value) {
        server.renewLease(leaseId, value);
    }

}

5. Server with Custom DGC Server

import java.rmi.*;
import java.rmi.server.*;
import java.rmi.dgc.*;
import java.util.*;

public class RMICustomDGCServer extends RMIDGCServer, UnicastRemoteObject {

    private Map<Long, Lease> leases = new HashMap<>();

    public RMICustomDGCServer() throws RemoteException {
        super();
    }

    @Override
    public Lease renewLease(Remote ref, long value, long leaseDuration) throws RemoteException {
        long leaseId = ref.hashCode();
        synchronized (leases) {
            leases.put(leaseId, new Lease(value, leaseDuration));
        }
        return new Lease(value, leaseDuration);
    }

    @Override
    public void clean(long leaseId, long renewId, Remote ref) {
        synchronized (leases) {
            leases.remove(leaseId);
        }
    }

}

6. Client with Custom Invocation Handler

import java.lang.reflect.*;
import java.rmi.*;
import java.rmi.dgc.*;

public class RMICustomInvocationHandler implements InvocationHandler {

    private Remote remote;
    private RMIDGCServer dgc;

    public RMICustomInvocationHandler(Remote remote, RMIDGCServer dgc) {
        this.remote = remote;
        this.dgc = dgc;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        try {
            return method.invoke(remote, args);
        } catch (InvocationTargetException e) {
            if (e.getTargetException() instanceof RemoteException) {
                dgc.lease(remote, 60000, 120000);
            }
            throw e.getTargetException();
        }
    }

}

7. Server with Custom Socket Factory

import java.rmi.*;
import java.rmi.server.*;
import java.rmi.dgc.*;
import java.net.*;

public class RMICustomSocketFactory extends UnicastRemoteObject implements RMISocketFactory {

    public RMICustomSocketFactory() throws RemoteException {
        super();
    }

    @Override
    public ServerSocket createServerSocket(int port) throws IOException {
        RMISocketFactory defaultFactory = RMISocketFactory.getDefaultSocketFactory();
        ServerSocket serverSocket = defaultFactory.createServerSocket(port);
        // Apply custom settings to the server socket
        return serverSocket;
    }

    @Override
    public Socket createSocket(String host, int port) throws IOException {
        RMISocketFactory defaultFactory = RMISocketFactory.getDefaultSocketFactory();
        Socket socket = defaultFactory.createSocket(host, port);
        // Apply custom settings to the socket
        return socket;
    }

}

8. Client with Custom Object Input Stream

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.dgc.*;
import java.io.*;

public class RMICustomObjectInputStream extends ObjectInputStream {

    private RMIDGCServer dgc;

    public RMIC