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The Object Composition library merges multiple Java objects into a single multi-subject object.
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/*
 * Copyright (c) 2007-2009, James Leigh All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * - Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution. 
 * - Neither the name of the openrdf.org nor the names of its contributors may
 *   be used to endorse or promote products derived from this software without
 *   specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 */
package org.openrdf.repository.object.managers.converters;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import org.openrdf.model.Literal;
import org.openrdf.model.URI;
import org.openrdf.model.ValueFactory;
import org.openrdf.model.impl.ValueFactoryImpl;
import org.openrdf.repository.object.exceptions.ObjectConversionException;
import org.openrdf.repository.object.managers.Marshall;

/**
 * Converts serializable objects to and from Literal.
 * 
 * @author James Leigh
 */
public class ObjectSerializationMarshall implements Marshall {
	private static final String pseudo[] = { "0", "1", "2", "3", "4", "5", "6", "7", "8",
			"9", "A", "B", "C", "D", "E", "F" };
	private ValueFactory vf;

	private Class type;

	private URI datatype;

	public ObjectSerializationMarshall(ValueFactory vf, Class type) {
		super();
		this.vf = vf;
		this.type = type;
		this.datatype = ValueFactoryImpl.getInstance().createURI("java:", type.getName());
	}

	public String getJavaClassName() {
		return type.getName();
	}

	public URI getDatatype() {
		return datatype;
	}

	public void setDatatype(URI datatype) {
		this.datatype = datatype;
	}

	public T deserialize(Literal literal) {
		try {
			byte[] decoded = decode(literal.getLabel());
			InputStream is = new ByteArrayInputStream(decoded);
			ObjectInputStream ois = new ObjectInputStream(is);
			Object result = ois.readObject();
			ois.close();
			return type.cast(result);
		} catch (ObjectConversionException e) {
			throw e;
		} catch (Exception e) {
			throw new ObjectConversionException(e);
		}
	}

	public Literal serialize(T object) {
		try {
			ByteArrayOutputStream bos = new ByteArrayOutputStream(1024);
			ObjectOutputStream oos = new ObjectOutputStream(bos);
			oos.writeObject(object);
			oos.close();
			byte[] byteArray = bos.toByteArray();
			String label = encode(byteArray);
			return vf.createLiteral(label, datatype);
		} catch (ObjectConversionException e) {
			throw e;
		} catch (Exception e) {
			throw new ObjectConversionException(e);
		}
	}

	private String encode(byte[] in) {
		StringBuilder out = new StringBuilder(in.length * 2);
		for (int i = 0; i < in.length; i++) {
			byte ch = (byte) (in[i] & 0xF0);
			ch = (byte) (ch >>> 4);
			ch = (byte) (ch & 0x0F);
			out.append(pseudo[ch]);
			ch = (byte) (in[i] & 0x0F);
			out.append(pseudo[ch]);
		}
		return out.toString();
	}

	private byte[] decode(String str) {
		char[] in = str.toCharArray();
        byte[] out = new byte[in.length / 2];
        if (in.length % 2 == 1)
            throw new ObjectConversionException("Hex String must be an odd number of characters");
        int j = 0;
        for (int i = 0; i < out.length; i++) {
            int most = Character.digit(in[j++], 16);
            int least = Character.digit(in[j++], 16);
			int value = most << 4 | least;
            out[i] = (byte) (value & 0xFF);
        }
        return out;
	}
}