https://github.com/javaee/jpa-spec: Java(TM) Persistence API 
Copyright (c) 2011 - 2013 Oracle Corporation. All rights reserved.
This program and the accompanying materials are made available under the
terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
which accompanies this distribution.
The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
and the Eclipse Distribution License is available at
http://www.eclipse.org/org/documents/edl-v10.php.
Contributors:
    Linda DeMichiel - Java Persistence 2.1

/*******************************************************************************
 * Copyright (c) 2011 - 2013 Oracle Corporation. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Linda DeMichiel - Java Persistence 2.1
 *
 ******************************************************************************/
package javax.persistence;


A class that implements this interface can be used to convert 
entity attribute state into database column representation 
and back again.
Note that the X and Y types may be the same Java type.

Type parameters:
  • <X> –  the type of the entity attribute
  • <Y> –  the type of the database column
/**
 * A class that implements this interface can be used to convert 
 * entity attribute state into database column representation 
 * and back again.
 * Note that the X and Y types may be the same Java type.
 *
 * @param <X>  the type of the entity attribute
 * @param <Y>  the type of the database column
 */
public interface AttributeConverter<X,Y> {

    
Converts the value stored in the entity attribute into the 
data representation to be stored in the database.

Params:
  • attribute –  the entity attribute value to be converted
Returns: the converted data to be stored in the database 
         column
/**
     * Converts the value stored in the entity attribute into the 
     * data representation to be stored in the database.
     *
     * @param attribute  the entity attribute value to be converted
     * @return  the converted data to be stored in the database 
     *          column
     */
    public Y convertToDatabaseColumn (X attribute);

    
Converts the data stored in the database column into the 
value to be stored in the entity attribute.
Note that it is the responsibility of the converter writer to
specify the correct dbData type for the corresponding 
column for use by the JDBC driver: i.e., persistence providers are 
not expected to do such type conversion.

Params:
  • dbData –  the data from the database column to be 
               converted
Returns: the converted value to be stored in the entity 
         attribute
/**
     * Converts the data stored in the database column into the 
     * value to be stored in the entity attribute.
     * Note that it is the responsibility of the converter writer to
     * specify the correct <code>dbData</code> type for the corresponding 
     * column for use by the JDBC driver: i.e., persistence providers are 
     * not expected to do such type conversion.
     *
     * @param dbData  the data from the database column to be 
     *                converted
     * @return  the converted value to be stored in the entity 
     *          attribute
     */
    public X convertToEntityAttribute (Y dbData);
}