Sample of looking up the node associated with a given key on Couchbase.

VbucketLookup.java

/**
 * Copyright 2013, Couchbase, Inc.  All rights reserved.
 */

package com.couchbase.demo.vbucketlookup;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Properties;
import java.util.concurrent.TimeUnit;
import java.util.logging.ConsoleHandler;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.naming.ConfigurationException;
import net.spy.memcached.MemcachedClient;
import net.spy.memcached.MemcachedNode;
import net.spy.memcached.NodeLocator;
import com.couchbase.client.CouchbaseClient;

/**
 * Look up the node associated with a given vbucket.
 *
 * WARNING: This is intended ONLY as a diagnosis tool.  In general
 * an application should not be aware of the location a given data
 * item is assigned to.  Also, note that the configuration can change
 * at any time, so the lookup you may do associated with a given key may
 * be _invalid_ by the time you request the actual operation via the
 * client object method.
 *
 */
public class VbucketLookup {

    public static void main(String args[]) {
        if (args.length < 2) {
            System.err.println("Usage: java -jar spyHashTest.jar http://my.server:8091 keyToFind");
            System.exit(1);
        }

        URI bootUri = null;

        try {
            bootUri = new URI(args[0]);
        } catch (URISyntaxException ex) {
            Logger.getLogger(VbucketLookup.class.getName()).log(Level.SEVERE, "Invalid URI specified: " + args[1] + "\nCannot continue.", ex);
        }

        VbucketLookup looker = new VbucketLookup();
        looker.lookupKey(bootUri, args[1]);

    }


    private void lookupKey(URI bootstrap, String key) {

        String bucketName = "default";
        ArrayList<URI> uriList = new ArrayList();
        uriList.add(bootstrap);
        MemcachedClient cbc = null;
        try {
            cbc = new CouchbaseClient(uriList, bucketName, "", "");
        } catch (IOException ex) {
            Logger.getLogger(VbucketLookup.class.getName()).log(Level.SEVERE, "Could not connect to server.  IOException received.", ex);
            System.err.println(ex.getCause());
        }

        NodeLocator nodeLocator = cbc.getNodeLocator();
        nodeLocator.getReadonlyCopy();
        MemcachedNode primary = nodeLocator.getPrimary(key);
        String nodeString = primary.toString();
        String nodeSubstr = nodeString.substring(nodeString.indexOf("/") + 1, nodeString.indexOf(","));
        System.out.println(key + " hashes to node " + nodeSubstr + " for " + bucketName + " bucket.");

        cbc.shutdown(10, TimeUnit.SECONDS);
    }

}

Output like:
Matt hashes to node 127.0.0.1:11210 for default bucket.