GenericEnumUserType.java

/*
 * Copyright 2014 The Sculptor Project Team, including 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 org.sculptor.framework.accessimpl;

import java.io.Serializable;
import java.lang.reflect.Method;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

import org.hibernate.HibernateException;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.type.AbstractSingleColumnStandardBasicType;
import org.hibernate.type.TypeResolver;
import org.hibernate.usertype.ParameterizedType;
import org.hibernate.usertype.UserType;

/**
 * Implements a generic enum user type identified / represented by a single identifier / column.
 * <p><ul>
 *    <li>The enum type being represented by the certain user type must be set
 *        by using the 'enumClass' property.</li>
 *    <li>The identifier representing a enum value is retrieved by the identifierMethod.
 *        The name of the identifier method can be specified by the
 *        'identifierMethod' property and by default the name() method is used.</li>
 *    <li>The identifier type is automatically determined by
 *        the return-type of the identifierMethod.</li>
 *    <li>The valueOfMethod is the name of the static factory method returning
 *        the enumeration object being represented by the given indentifier.
 *        The valueOfMethod's name can be specified by setting the 'valueOfMethod'
 *        property. The default valueOfMethod's name is 'valueOf'.</li>
 * </p>
 * <p>
 * Example of an enum type represented by an int value:
 * <pre>
 * public enum SimpleNumber {
 *   Unknown(-1), Zero(0), One(1), Two(2), Three(3);
 *   private int value;
 *   private SimpleNumber(int value) {
 *       this.value = value;
 *   }
 *
 *   public int toInt() { return value; }
 *   public SimpleNumber fromInt(int value) {
 *         switch(value) {
 *          case 0: return Zero;
 *         case 1: return One;
 *         case 2: return Two;
 *         case 3: return Three;
 *         default:
 *                 return Unknown;
 *     }
 *   }
 * }
 * </pre>
 * <p>
 * The Mapping would look like this:
 * <pre>
 *    <typedef name="SimpleNumber" class="GenericEnumUserType">
 *        <param name="enumClass">SimpleNumber</param>
 *        <param name="identifierMethod">toInt</param>
 *        <param name="valueOfMethod">fromInt</param>
 *    </typedef>
 *    <class ...>
 *      ...
 *     <property name="number" type="SimpleNumber"/>
 *    </class>
 * </pre>
 *
 * @author Martin Kersten
 */
@SuppressWarnings("rawtypes")
public class GenericEnumUserType implements UserType, ParameterizedType, Serializable {

	private static final long serialVersionUID = -3519064203142497321L;

	private static final String DEFAULT_IDENTIFIER_METHOD_NAME = "name";
	private static final String DEFAULT_VALUE_OF_METHOD_NAME = "valueOf";

	private Class<? extends Enum> enumClass;
	private Class<?> identifierType;
	private Method identifierMethod;
	private Method valueOfMethod;
	private AbstractSingleColumnStandardBasicType type;
	private int[] sqlTypes;

	@Override
	public void setParameterValues(final Properties parameters) {
		final String enumClassName = parameters.getProperty("enumClass");
		try {
			enumClass = Class.forName(enumClassName).asSubclass(Enum.class);
		} catch (final ClassNotFoundException cfne) {
			throw new HibernateException("Enum class not found", cfne);
		}

		final String identifierMethodName = parameters.getProperty("identifierMethod", DEFAULT_IDENTIFIER_METHOD_NAME);

		try {
			identifierMethod = enumClass.getMethod(identifierMethodName, new Class[0]);
			identifierType = identifierMethod.getReturnType();
		} catch (final Exception e) {
			throw new HibernateException("Failed to obtain identifier method", e);
		}

		final TypeResolver tr = new TypeResolver();
		type = (AbstractSingleColumnStandardBasicType) tr.basic(identifierType.getName());

		if (type == null) {
			throw new HibernateException("Unsupported identifier type " + identifierType.getName());
		}

		sqlTypes = new int[] { type.sqlType() };

		final String valueOfMethodName = parameters.getProperty("valueOfMethod", DEFAULT_VALUE_OF_METHOD_NAME);

		try {
			valueOfMethod = enumClass.getMethod(valueOfMethodName, new Class[] { identifierType });
		} catch (final Exception e) {
			throw new HibernateException("Failed to obtain valueOf method", e);
		}
	}

	@Override
	public Class<? extends Enum> returnedClass() {
		return enumClass;
	}

	@Override
	public Object nullSafeGet(final ResultSet rs, final String[] names, final SessionImplementor sessionImplementor, final Object owner) throws HibernateException,
			SQLException {
		final Object identifier = type.nullSafeGet(rs, names[0], sessionImplementor);
		if (identifier == null) {
			return null;
		}

		try {
			return valueOfMethod.invoke(enumClass, new Object[] { identifier });
		} catch (final Exception e) {
			throw new HibernateException("Exception while invoking valueOf method '" + valueOfMethod.getName()
					+ "' of " + "enumeration class '" + enumClass + "'", e);
		}
	}

	@Override
	public void nullSafeSet(final PreparedStatement st, final Object value, final int index, final SessionImplementor sessionImplementor) throws HibernateException,
			SQLException {
		try {
			if (value == null) {
				st.setNull(index, type.sqlType());
			} else {
				final Object identifier = identifierMethod.invoke(value, new Object[0]);
				type.nullSafeSet(st, identifier, index, sessionImplementor);
			}
		} catch (final Exception e) {
			throw new HibernateException("Exception while invoking identifierMethod '" + identifierMethod.getName()
					+ "' of " + "enumeration class '" + enumClass + "'", e);
		}
	}

	@Override
	public int[] sqlTypes() {
		return sqlTypes;
	}

	@Override
	public Object assemble(final Serializable cached, final Object owner) throws HibernateException {
		return cached;
	}

	@Override
	public Object deepCopy(final Object value) throws HibernateException {
		return value;
	}

	@Override
	public Serializable disassemble(final Object value) throws HibernateException {
		return (Serializable) value;
	}

	@Override
	public boolean equals(final Object x, final Object y) throws HibernateException {
		return x == y;
	}

	@Override
	public int hashCode(final Object x) throws HibernateException {
		return x.hashCode();
	}

	@Override
	public boolean isMutable() {
		return false;
	}

	@Override
	public Object replace(final Object original, final Object target, final Object owner) throws HibernateException {
		return original;
	}

}