/*
* Copyright 2016 Wim Deblauwe. All Rights Reserved.
*
* 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.github.benmanes.caffeine.examples.writebehind.rxjava;
import static java.util.Objects.requireNonNull;
import static java.util.stream.Collectors.toMap;
import java.util.AbstractMap.SimpleImmutableEntry;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.TimeUnit;
import java.util.function.BinaryOperator;
import java.util.function.Consumer;
import com.github.benmanes.caffeine.cache.CacheWriter;
import com.github.benmanes.caffeine.cache.RemovalCause;
import io.reactivex.subjects.PublishSubject;
/**
* This class implements the {@link CacheWriter} interface to allow a cache to have "write-behind"
* semantics. The passed in writeAction will only be called every 'bufferTime' time with a Map
* containing the keys and the values that have been updated in the cache each time.
* <p>
* If a key is updated multiple times during that period then the 'binaryOperator' has to decide
* which value should be taken.
* <p>
* An example usage of this class is keeping track of users and their activity on a web site. You
* don't want to update the database each time any of your users does something. It is better to
* batch the updates every x seconds and just write the most recent time in the database.
*
* @param <K> the type of the key in the cache
* @param <V> the type of the value in the cache
* @author wim.deblauwe@gmail.com (Wim Deblauwe)
*/
public final class WriteBehindCacheWriter<K, V> implements CacheWriter<K, V> {
private final PublishSubject<Entry<K, V>> subject;
private WriteBehindCacheWriter(Builder<K, V> builder) {
subject = PublishSubject.create();
subject.buffer(builder.bufferTimeNanos, TimeUnit.NANOSECONDS)
.map(entries -> entries.stream().collect(
toMap(Entry::getKey, Entry::getValue, builder.coalescer)))
.subscribe(builder.writeAction::accept);
}
@Override
public void write(K key, V value) {
subject.onNext(new SimpleImmutableEntry<>(key, value));
}
@Override
public void delete(K key, V value, RemovalCause removalCause) {}
public static final class Builder<K, V> {
private Consumer<Map<K, V>> writeAction;
private BinaryOperator<V> coalescer;
private long bufferTimeNanos;
/**
* The duration that the calls to the cache should be buffered before calling the
* <code>writeAction</code>.
*/
public Builder<K, V> bufferTime(long duration, TimeUnit unit) {
this.bufferTimeNanos = TimeUnit.NANOSECONDS.convert(duration, unit);
return this;
}
/** The callback to perform the writing to the database or repository. */
public Builder<K, V> writeAction(Consumer<Map<K, V>> writeAction) {
this.writeAction = requireNonNull(writeAction);
return this;
}
/** The action that decides which value to take in case a key was updated multiple times. */
public Builder<K, V> coalesce(BinaryOperator<V> coalescer) {
this.coalescer = requireNonNull(coalescer);
return this;
}
/** Returns a {@link CacheWriter} that batches writes to the system of record. */
public WriteBehindCacheWriter<K, V> build() {
return new WriteBehindCacheWriter<>(this);
}
}
}