org.usergrid.persistence.query.ir.result.UnionIterator.java Source code

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Here is the source code for org.usergrid.persistence.query.ir.result.UnionIterator.java

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/*******************************************************************************
 * Copyright 2012 Apigee Corporation
 * 
 * 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 org.usergrid.persistence.query.ir.result;

import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.UUID;

import org.usergrid.persistence.cassandra.CursorCache;

import com.google.common.collect.Sets;

/**
 * Simple iterator to perform Unions
 * 
 * @author tnine
 * 
 */
public class UnionIterator extends MultiIterator {

    /**
     * results that were left from our previous union. These are kept and returned
     * before advancing iterators
     */
    private Set<UUID> remainderResults;

    private int currentIndex = -1;

    /**
     * @param pageSize
     */
    public UnionIterator(int pageSize) {
        super(pageSize);
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.usergrid.persistence.query.ir.result.MergeIterator#advance()
     */
    @Override
    protected Set<UUID> advance() {

        int size = iterators.size();

        if (size == 0) {
            return null;
        }

        Set<UUID> resultSet = null;

        if (remainderResults != null) {
            resultSet = remainderResults;
            remainderResults = null;
        } else {
            resultSet = new LinkedHashSet<UUID>();
        }

        /**
         * We have results from a previous merge
         */

        int complete = 0;

        while (resultSet.size() < pageSize && complete < size) {

            currentIndex = (currentIndex + 1) % iterators.size();

            ResultIterator itr = iterators.get(currentIndex);

            if (!itr.hasNext()) {
                complete++;
                continue;
            }

            resultSet = Sets.union(resultSet, itr.next());

        }

        // now check if we need to split our results if they went over the page size
        if (resultSet.size() > pageSize) {
            Set<UUID> returnSet = new LinkedHashSet<UUID>(pageSize);

            Iterator<UUID> itr = resultSet.iterator();

            for (int i = 0; i < pageSize && itr.hasNext(); i++) {
                returnSet.add(itr.next());
            }

            remainderResults = new LinkedHashSet<UUID>(pageSize);

            while (itr.hasNext()) {
                remainderResults.add(itr.next());
            }

            resultSet = returnSet;
        }

        return resultSet;

    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * org.usergrid.persistence.query.ir.result.ResultIterator#finalizeCursor(
     * org.usergrid.persistence.cassandra.CursorCache)
     */
    @Override
    public void finalizeCursor(CursorCache cache, UUID lastLoaded) {
        //we can create a cursor for every iterator in our union
        for (ResultIterator current : iterators) {
            current.finalizeCursor(cache, lastLoaded);
        }
    }

}