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This geoLatte-geom library offers a geometry model that conforms to the OGC Simple Features for SQL specification.
There is a newer version: 1.9.1
/*
 * This file is part of the GeoLatte project.
 *
 *     GeoLatte is free software: you can redistribute it and/or modify
 *     it under the terms of the GNU Lesser General Public License as published by
 *     the Free Software Foundation, either version 3 of the License, or
 *     (at your option) any later version.
 *
 *     GeoLatte is distributed in the hope that it will be useful,
 *     but WITHOUT ANY WARRANTY; without even the implied warranty of
 *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *     GNU Lesser General Public License for more details.
 *
 *     You should have received a copy of the GNU Lesser General Public License
 *     along with GeoLatte.  If not, see .
 *
 * Copyright (C) 2010 - 2011 and Ownership of code is shared by:
 * Qmino bvba - Romeinsestraat 18 - 3001 Heverlee  (http://www.qmino.com)
 * Geovise bvba - Generaal Eisenhowerlei 9 - 2140 Antwerpen (http://www.geovise.com)
 */

package org.geolatte.geom.codec;

import org.geolatte.geom.ByteBuffer;
import org.geolatte.geom.ByteOrder;
import org.geolatte.geom.Geometry;

import java.util.HashMap;
import java.util.Map;

/**
 * Creates encoders/decoders for WKB geometry representations.
 *
 * Note that the WkbEncoder/WkbDecoder instances returned by the factory
 * methods are not thread-safe.
 *
 * @author Karel Maesen, Geovise BVBA
 *         creation-date: Oct 29, 2010
 */
public class Wkb {

    public enum Dialect {
        //the PostGIS EWKB dialect (versions 1.0 to 1.6).
        POSTGIS_EWKB_1,
        MYSQL_WKB
    }

    private static final Dialect DEFAULT_DIALECT = Dialect.POSTGIS_EWKB_1;

    private static final Map> DECODERS = new HashMap>();
    private static final Map> ENCODERS = new HashMap>();

    static {
        DECODERS.put(Dialect.POSTGIS_EWKB_1, PostgisWkbDecoder.class);
        DECODERS.put(Dialect.MYSQL_WKB, MySqlWkbDecoder.class);
        ENCODERS.put(Dialect.POSTGIS_EWKB_1, PostgisWkbEncoder.class);
        ENCODERS.put(Dialect.MYSQL_WKB, MySqlWkbEncoder.class);
    }


    /**
     * Encodes a Geometry into a WKB representation using the NDR (little-endian)  byte-order.
     *
     * This methods uses the default WKB dialect (Postgis v1.5 EWKB ).
     *
     * @param geometry The Geometry to be encoded as WKB.
     * @return A buffer of bytes that contains the WKB-encoded Geometry.
     */
    public static ByteBuffer toWkb(Geometry geometry) {
        return toWkb(geometry, ByteOrder.NDR);
    }

    /**
     * Encodes a Geometry into a WKB representation using the specified byte-order.
     * This methods uses the default WKB dialect (Postgis v1.5 EWKB ).
     *
     * @param geometry  The Geometry to be encoded as WKB.
     * @param byteOrder The WKB byte order, either {@link ByteOrder#XDR XDR} or {@link ByteOrder#NDR NDR}
     * @return A buffer of bytes that contains the WKB-encoded Geometry.
     */
    public static ByteBuffer toWkb(Geometry geometry, ByteOrder byteOrder) {
        WkbEncoder encoder = newEncoder(DEFAULT_DIALECT);
        return encoder.encode(geometry, byteOrder);
    }

    /**
     * Decodes a WKB representation in a ByteBuffer to a Geometry.
     * This methods uses the default WKB dialect (Postgis v1.5 EWKB ).
     *
     * @param byteBuffer A buffer of bytes that contains a WKB-encoded Geometry.
     * @return The Geometry that is encoded in the WKB.
     */
    public static Geometry fromWkb(ByteBuffer byteBuffer) {
        WkbDecoder decoder = newDecoder(DEFAULT_DIALECT);
        return decoder.decode(byteBuffer);
    }

    /**
     * Creates a WkbDecoder for the specified WKB Dialect.
     *
     * @param dialect the WKB dialect
     * @return an WkbDecoder that supports the specified dialect
     */
    public static WkbDecoder newDecoder(Dialect dialect) {
        Class decoderClass = DECODERS.get(dialect);
        assert (decoderClass != null) : "A variant declared, but no encoder/decoder registered.";
        return createInstance(decoderClass);
    }

    /**
     * Creates a WkbDecoder for the default WKB Dialect.
     *
     * @return an WkbDecoder that supports the specified dialect
     */
    public static WkbDecoder newDecoder() {
        Class decoderClass = DECODERS.get(DEFAULT_DIALECT);
        assert (decoderClass != null) : "A variant declared, but no encoder/decoder registered.";
        return createInstance(decoderClass);
    }


    /**
     * Creates a WkbEncoder for the specified WKB Dialect.
     *
     * @param dialect the WKB dialect
     * @return an WkbEncoder that supports the specified dialect
     */
    public static WkbEncoder newEncoder(Dialect dialect) {
        Class decoderClass = ENCODERS.get(dialect);
        assert (decoderClass != null) : "A variant declared, but no encoder/decoder registered.";
        return createInstance(decoderClass);
    }

    /**
     * Creates a WkbEncoder for the default WKB Dialect.
     *
     * @return an WkbEncoder that supports the specified dialect
     */
    public static WkbEncoder newEncoder() {
        Class decoderClass = ENCODERS.get(DEFAULT_DIALECT);
        assert (decoderClass != null) : "A variant declared, but no encoder/decoder registered.";
        return createInstance(decoderClass);
    }

    private static  T createInstance(Class codecClass) {
        if (codecClass == null) {
            throw new IllegalArgumentException("Null WKB codec class argument not allowed.");
        }
        try {
            return codecClass.newInstance();
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

}