org.opendatakit.aggregate.odktables.Sequencer.java Source code

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Here is the source code for org.opendatakit.aggregate.odktables.Sequencer.java

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/*
 * Copyright (C) 2013 University of Washington
 *
 * 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.opendatakit.aggregate.odktables;

import org.apache.commons.lang3.StringUtils;
import org.opendatakit.aggregate.server.ServerPreferencesProperties;
import org.opendatakit.common.persistence.exception.ODKEntityNotFoundException;
import org.opendatakit.common.persistence.exception.ODKOverQuotaException;
import org.opendatakit.common.web.CallingContext;

/**
 * Impose a strict ordering on the log entries associated with a file. The
 * ordering consists of two concatentated counters:
 *
 * sequenceBase.counter
 *
 * Where sequenceBase is a value that is fetched, incremented and written to the
 * datastore via
 *
 * ServerPreferencesProperties.unsafeIncOdkTablesSequencerBase(cc).
 *
 * This is obtained when the Sequencer is created, which is at the time the
 * update lock is obtained.
 *
 * Counter is simply a counter held within this object instance to order the
 * updates occuring during the holding of the lock.
 *
 * @author mitchellsundt@gmail.com
 *
 */
public class Sequencer {

    private static final int DECIMAL_PLACES = 10;
    private final String sequenceBase;
    private int counter;

    /**
     * Obtain a sequencer from the datastore. Should be called immediately after
     * the update lock has been obtained, and released whenever the lock is
     * released.
     *
     * @param cc
     * @throws ODKEntityNotFoundException
     * @throws ODKOverQuotaException
     */
    Sequencer(CallingContext cc) throws ODKEntityNotFoundException, ODKOverQuotaException {
        sequenceBase = ServerPreferencesProperties.unsafeIncOdkTablesSequencerBase(cc);
        counter = 0;
    }

    /**
     * Generate the next sequence value.
     *
     * Use seq1.compareTo(seq2) as the natural ordering of these values.
     *
     * @return
     */
    public String getNextSequenceValue() {
        ++counter;
        return sequenceBase + "." + StringUtils.leftPad(Integer.toString(counter), DECIMAL_PLACES, '0');
    }
}