Sample of using `java.lang.reflect.Proxy`

ProxySample.java

package scratch;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;

public class ProxySample {

    public interface Iface {
        public String uppercase(String forWho, String value);
        public int add1(String forwho, int value);
    }

    public static class LocalImpl implements Iface {
        @Override
        public String uppercase(String forWho, String value) {
            System.out.println("Local impl uppercasing " + value);
            return value.toUpperCase();
        }

        @Override
        public int add1(String forwho, int value) {
            System.out.println("Local impl adding one to " + value);
            return value + 1;
        }
    }

    public static class RemoteImpl implements Iface {
        @Override
        public String uppercase(String forWho, String value) {
            System.out.println("Pretend I'm remote machine; uppercasing " + value);
            return value.toUpperCase();
        }

        @Override
        public int add1(String forwho, int value) {
            System.out.println("Pretend I'm a remote machine; adding one to " + value);
            return value + 1;
        }
    }

    public static Iface getSuitableServerFor(String email) {
        return new RemoteImpl();
    }

    public static Iface makeDistributed(final Iface local) {
        return (Iface) Proxy.newProxyInstance(
                Iface.class.getClassLoader(),
                new Class<?>[] { Iface.class },
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        if (args.length < 1 || ! (args[0] instanceof String))
                            throw new IllegalArgumentException("String email required as first argument");

                        String email = (String) args[0];
                        Iface target;
                        if (email.contains("remote")) {
                            target = getSuitableServerFor(email);
                        } else {
                            target = local;
                        }

                        try {
                            return method.invoke(target, args);
                        } catch (InvocationTargetException e) {
                            // The implementing method threw an exception; propagate the original
                            throw e.getCause();
                        } catch (IllegalAccessException e) {
                            throw new RuntimeException("Reflection failed?", e);
                        }
                    }
                }
        );
    }

    public static void main (String[] args) {
        Iface local = new LocalImpl();
        Iface distributed = makeDistributed(local);
        // start serving `distributed`

        for (String who : Arrays.asList("[email protected]", "[email protected]")) {
            System.out.println("42 + 1 =  " + distributed.add1(who, 42));
            System.out.println("blurp:    " + distributed.uppercase(who, "blurp"));
        }
    }
}

Expected output:

Local impl adding one to 42
42 + 1 =  43
Local impl uppercasing blurp
blurp:    BLURP
Pretend I'm a thrift client; adding one to 42
42 + 1 =  43
Pretend I'm a thrift client; uppercasing blurp
blurp:    BLURP