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The MongoDB Connector for Hadoop is a plugin for Hadoop that provides the ability to use MongoDB as an input source and/or an output destination.

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/*
 * Copyright 2010-2013 10gen 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.mongodb.hadoop.splitter;

import com.mongodb.MongoClientURI;
import com.mongodb.hadoop.input.MongoInputSplit;
import com.mongodb.hadoop.util.MongoConfigUtil;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapreduce.InputSplit;

import java.util.Collections;
import java.util.List;

import static java.lang.String.format;

/* This implementation of MongoSplitter does not actually
 * do any splitting, it will just create a single input split
 * which represents the entire data set within a collection.
 */
public class SingleMongoSplitter extends MongoCollectionSplitter {

    private static final Log LOG = LogFactory.getLog(SingleMongoSplitter.class);

    //Create a single split which consists of a single
    //a query over the entire collection.


    public SingleMongoSplitter() {
    }

    public SingleMongoSplitter(final Configuration conf) {
        super(conf);
    }

    @Override
    public List calculateSplits() {
        if (LOG.isDebugEnabled()) {
            MongoClientURI inputURI =
              MongoConfigUtil.getInputURI(getConfiguration());
            LOG.debug(format("SingleMongoSplitter calculating splits for namespace: %s.%s; hosts: %s",
                inputURI.getDatabase(), inputURI.getCollection(), inputURI.getHosts()));
        }
        return Collections.singletonList(
          (InputSplit) new MongoInputSplit(getConfiguration()));
    }

}