UUIDIdentityGenerator.java

/*
 * Copyright (c) 2014 the original author or authors
 *
 * 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 io.werval.util;

import java.util.UUID;
import java.util.concurrent.atomic.AtomicLong;

/**
 * UUID based IdentityGenerator.
 * <p>
 * Generated identities have the following form: {@literal (PREFIX_)UUID_COUNT}.
 * <p>
 * {@literal PREFIX} is optional, see {@link #UUIDIdentityGenerator(java.lang.String)}
 * and {@link #UUIDIdentityGenerator(java.lang.String, int)}.
 * <p>
 * {@literal COUNT} can be left-padded with zeroes, see {@link #UUIDIdentityGenerator(int)}
 * and {@link #UUIDIdentityGenerator(java.lang.String, int)}.
 * <p>
 * Each instance holds a {@link UUID} and an {@link AtomicLong} based counter.
 * Identities are generated by concatenating the UUID and the counter.
 * The later is incremented along the way.
 */
public final class UUIDIdentityGenerator
    implements IdentityGenerator
{
    private final int countLength;
    private final String prefix;
    private String prefixedUuid;
    private AtomicLong counter;

    public UUIDIdentityGenerator()
    {
        this( Strings.EMPTY, -1 );
    }

    /**
     * Use this constructor to left-pad counter with zeroes.
     *
     * @param countLength Length of the COUNT part of the generated identities.
     *                    A negative value disable padding.
     */
    public UUIDIdentityGenerator( int countLength )
    {
        this( Strings.EMPTY, countLength );
    }

    /**
     * Use this constructor to prefix the identities.
     *
     * @param prefix String to prepend to all generated identities
     */
    public UUIDIdentityGenerator( String prefix )
    {
        this( prefix, -1 );
    }

    /**
     * Use this constructor to prefix the identities and left-pad the counter with zeroes.
     *
     * @param prefix      String to prepend to all generated identities
     * @param countLength Length of the COUNT part of the generated identities.
     *                    A negative value disable padding.
     */
    public UUIDIdentityGenerator( String prefix, int countLength )
    {
        this.prefix = prefix;
        this.countLength = countLength;
        reset();
    }

    @Override
    public String newIdentity()
    {
        if( countLength > 0 )
        {
            String padFormat = "%0" + ( countLength ) + "d";
            return prefixedUuid + String.format( padFormat, counter.getAndIncrement() );
        }
        return prefixedUuid + counter.getAndIncrement();
    }

    /**
     * Reset the identity UUID & counter.
     */
    public synchronized void reset()
    {
        StringBuilder sb = new StringBuilder();
        if( Strings.hasText( prefix ) )
        {
            sb.append( prefix ).append( "_" );
        }
        sb.append( UUID.randomUUID().toString() ).append( "_" );
        prefixedUuid = sb.toString();
        counter = new AtomicLong();
    }
}