com.spotify.dns.CachingLookupFactory.java Source code

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Here is the source code for com.spotify.dns.CachingLookupFactory.java

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/*
 * Copyright (c) 2015 Spotify AB
 *
 * 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.spotify.dns;

import com.google.common.base.Preconditions;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

import org.xbill.DNS.Lookup;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;

/**
 * Caches Lookup instances using a per-thread cache; this is so that different threads will never
 * get the same instance of Lookup. Lookup instances are not thread-safe.
 */
class CachingLookupFactory implements LookupFactory {
    private final LookupFactory delegate;
    private final ThreadLocal<Cache<String, Lookup>> cacheHolder;

    CachingLookupFactory(LookupFactory delegate) {
        this.delegate = Preconditions.checkNotNull(delegate, "delegate");
        cacheHolder = new ThreadLocal<Cache<String, Lookup>>() {
            @Override
            protected Cache<String, Lookup> initialValue() {
                return CacheBuilder.newBuilder().build();
            }
        };
    }

    @Override
    public Lookup forName(final String fqdn) {
        try {
            return cacheHolder.get().get(fqdn, new Callable<Lookup>() {
                @Override
                public Lookup call() {
                    return delegate.forName(fqdn);
                }
            });
        } catch (ExecutionException e) {
            throw new DnsException(e);
        }
    }
}