com.hazelcast.mapreduce.KeyValueSource Maven / Gradle / Ivy
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* Copyright (c) 2008-2016, Hazelcast, Inc. 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.hazelcast.mapreduce;
import com.hazelcast.core.IList;
import com.hazelcast.core.IMap;
import com.hazelcast.core.ISet;
import com.hazelcast.core.MultiMap;
import com.hazelcast.mapreduce.impl.ListKeyValueSource;
import com.hazelcast.mapreduce.impl.MapKeyValueSource;
import com.hazelcast.mapreduce.impl.MultiMapKeyValueSource;
import com.hazelcast.mapreduce.impl.SetKeyValueSource;
import com.hazelcast.spi.NodeEngine;
import com.hazelcast.spi.annotation.Beta;
import java.io.Closeable;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;
/**
* The abstract KeyValueSource class is used to implement custom data sources for mapreduce algorithms.
* Default shipped implementations contains KeyValueSources for Hazelcast data structures like
* {@link com.hazelcast.core.IMap} and {@link com.hazelcast.core.MultiMap}. Custom implementations could
* be external files, URLs or any other data source that can be visualized as key-value pairs.
*
* @param key type
* @param value type
* @since 3.2
*/
@Beta
public abstract class KeyValueSource
implements Closeable {
/**
* This method is called before accessing the key-value pairs of this KeyValueSource.
*
* @param nodeEngine nodeEngine of this cluster node
* @return true if the operation succeeded, false otherwise
*/
public abstract boolean open(NodeEngine nodeEngine);
/**
* Called to request if at least one more key-value pair is available from this
* data source. If so, this method returns true, otherwise it returns false.
*
* Calls to this method will change the state, more specifically if an element is found,
* the index will be set to the found element. Subsequent calls to the key() and element()
* methods will return that element.
*
* @return true if at least one more key-value pair is available from this
* data source, false otherwise.
*/
public abstract boolean hasNext();
/**
* Returns the current index key for {@link KeyPredicate} analysis. This is called
* to prevent a possible deserialization of unneeded values because the key is not
* interesting for the running mapreduce algorithm.
*
* Calls to this method won't change state.
*
* @return the current index key for {@link KeyPredicate} analysis
*/
public abstract K key();
/**
* Returns the current index element
*
* Calls to this method won't change state.
*
* @return the current index element
*/
public abstract Map.Entry element();
/**
* This method resets all internal state to be a new instance.
* The same instance of the KeyValueSource may be used multiple times in a row depending
* on the internal implementation, especially when the KeyValueSource implements
* {@link com.hazelcast.mapreduce.PartitionIdAware}.
* If the instance is reused, a sequence of reset(), {@link #open(com.hazelcast.spi.NodeEngine)}
* and {@link #close()} is called multiple times with the other methods between open(...) and close().
*
* @return true if reset was successful, false otherwise
*/
public abstract boolean reset();
/**
*
* If {@link #isAllKeysSupported()} returns true, a call to this method returns
* all clusterwide available keys. If there is no chance to precollect all keys due to
* partitioning of the data {@link #isAllKeysSupported()}, this method returns false.
*
*
* If this functionality is not available and {@link Job#onKeys(Object[])},
* {@link Job#onKeys(Iterable)}, or {@link Job#keyPredicate(KeyPredicate)} is used, a
* preselection of the interesting partitions / nodes is not available and the
* overall processing speed my be degraded.
*
*
* If {@link #isAllKeysSupported()} returns false this method throws an
* {@link java.lang.UnsupportedOperationException}.
*
*
* @return a collection of all clusterwide available keys
*/
public final Collection getAllKeys() {
if (!isAllKeysSupported()) {
throw new UnsupportedOperationException("getAllKeys is unsupported for this KeyValueSource");
}
return getAllKeys0();
}
/**
*
* If it is possible to collect all clusterwide available keys for this KeyValueSource
* implementation then this method returns true.
* If true is returned, a call to {@link #getAllKeys()} must return all available keys
* to execute a preselection of interesting partitions / nodes based on returns keys.
*
*
* If this functionality is not available and {@link Job#onKeys(Object[])},
* {@link Job#onKeys(Iterable)}, or {@link Job#keyPredicate(KeyPredicate)} is used, a
* preselection of the interesting partitions / nodes is not available and the
* overall processing speed my be degraded.
*
*
* @return true if collecting clusterwide keys is available, false otherwise
*/
public boolean isAllKeysSupported() {
return false;
}
/**
* This method is meant to be overridden to implement collecting of all clusterwide available keys
* and return them from {@link #getAllKeys()}.
*
* @return a collection of all clusterwide available keys
*/
protected Collection getAllKeys0() {
return Collections.emptyList();
}
/**
* A helper method to build a KeyValueSource implementation based on the specified {@link IMap}
*
* @param map map to build a KeyValueSource implementation
* @param key type of the map
* @param value type of the map
* @return KeyValueSource implementation based on the specified map
*/
public static KeyValueSource fromMap(IMap map) {
return new MapKeyValueSource(map.getName());
}
/**
* A helper method to build a KeyValueSource implementation based on the specified {@link MultiMap}
*
* @param multiMap multiMap to build a KeyValueSource implementation
* @param key type of the multiMap
* @param value type of the multiMap
* @return KeyValueSource implementation based on the specified multiMap
*/
public static KeyValueSource fromMultiMap(MultiMap multiMap) {
return new MultiMapKeyValueSource(multiMap.getName());
}
/**
* A helper method to build a KeyValueSource implementation based on the specified {@link IList}.
* The key returned by this KeyValueSource implementation is ALWAYS the name of the list itself,
* whereas the value are the entries of the list, one by one. This implementation behaves like a MultiMap
* with a single key but multiple values.
*
* @param list list to build a KeyValueSource implementation
* @param value type of the list
* @return KeyValueSource implementation based on the specified list
*/
public static KeyValueSource fromList(IList list) {
return new ListKeyValueSource(list.getName());
}
/**
* A helper method to build a KeyValueSource implementation based on the specified {@link ISet}.
* The key returned by this KeyValueSource implementation is ALWAYS the name of the set itself,
* whereas the value are the entries of the set, one by one. This implementation behaves like a MultiMap
* with a single key but multiple values.
*
* @param set set to build a KeyValueSource implementation
* @param value type of the set
* @return KeyValueSource implementation based on the specified set
*/
public static KeyValueSource fromSet(ISet set) {
return new SetKeyValueSource(set.getName());
}
}
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