com.datastax.driver.core.policies.WhiteListPolicy Maven / Gradle / Ivy

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A driver for Apache Cassandra 1.2+ that works exclusively with the Cassandra Query Language version 3 (CQL3) and Cassandra's binary protocol.

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/*
 *      Copyright (C) 2012-2015 DataStax Inc.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */
package com.datastax.driver.core.policies;

import com.datastax.driver.core.Host;
import com.google.common.base.Predicate;
import com.google.common.collect.ImmutableSet;

import java.net.InetSocketAddress;
import java.util.Collection;

/**
 * A load balancing policy wrapper that ensure that only hosts from a provided
 * white list will ever be returned.
 * 
 * This policy wraps another load balancing policy and will delegate the choice
 * of hosts to the wrapped policy with the exception that only hosts contained
 * in the white list provided when constructing this policy will ever be
 * returned. Any host not in the while list will be considered {@code IGNORED}
 * and thus will not be connected to.
 * 
 * This policy can be useful to ensure that the driver only connects to a
 * predefined set of hosts. Keep in mind however that this policy defeats
 * somewhat the host auto-detection of the driver. As such, this policy is only
 * useful in a few special cases or for testing, but is not optimal in general.
 * If all you want to do is limiting connections to hosts of the local
 * data-center then you should use DCAwareRoundRobinPolicy and *not* this policy
 * in particular.
 *
 * @see HostFilterPolicy
 */
public class WhiteListPolicy extends HostFilterPolicy {

    /**
     * Creates a new policy that wraps the provided child policy but only "allows" hosts
     * from the provided while list.
     *
     * @param childPolicy the wrapped policy.
     * @param whiteList   the white listed hosts. Only hosts from this list may get connected
     *                    to (whether they will get connected to or not depends on the child policy).
     */
    public WhiteListPolicy(LoadBalancingPolicy childPolicy, Collection whiteList) {
        super(childPolicy, buildPredicate(whiteList));
    }

    private static Predicate buildPredicate(Collection whiteList) {
        final ImmutableSet hosts = ImmutableSet.copyOf(whiteList);
        return new Predicate() {
            @Override
            public boolean apply(Host host) {
                return hosts.contains(host.getSocketAddress());
            }
        };
    }

}