com.persistit.encoding.ValueRenderer Maven / Gradle / Ivy
Show all versions of akiban-persistit Show documentation
/**
* Copyright © 2005-2012 Akiban Technologies, Inc. All rights reserved.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Public License v1.0 which
* accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* This program may also be available under different license terms.
* For more information, see www.akiban.com or contact [email protected].
*
* Contributors:
* Akiban Technologies, Inc.
*/
package com.persistit.encoding;
import com.persistit.Value;
import com.persistit.exception.ConversionException;
/**
*
* An extended {@link ValueCoder} that can populate a supplied
* Object with data that was formerly written to a {@link Value} by
* the ValueCoder.
*
*
* A ValueRenderer implements an additional method called
* {@link #render} that populates a supplied target object rather than creating
* a new object instance. The application provides the mutable target object to
* {@link Value#get(Object)}.
*
*
* A ValueRenderer can implement an application-level contract to
* recover a limited set of fields from an encoded Value or to
* populate a generic target object that might be suitable for utility display
* purposes. For example, suppose there is a complex Person class
* with many fields that refer to other objects. Deserializing and populating
* all the fields of such a Person object might not be appropriate
* in an area of the application that merely needs to display a list of names.
* To avoid completely deserializing numerous Person objects, the
* application could register a ValueRenderer implementation that
* knows how to decode a serialized Person into a
* PersonListData object. To do so it would {@link Value#get} the
* desired interior fields of the encoded Person and
* {@link Value#skip} the other fields.
*
*
*
* @version 1.0
*/
public interface ValueRenderer extends ValueCoder {
/**
*
* Populates the state of the supplied (mutable) target Object
* by decoding the supplied Value. This method will be called
* only if this ValueRenderer has been registered with the
* current {@link CoderManager} to encode objects having the supplied
* Class value. Persistit will never call this method to decode
* a value that was null when written because null values are
* handled by built-in encoding logic.
*
*
* @param value
* The Value from which interior fields of the
* object are to be retrieved
*
* @param target
* The object into which the decoded value is to be written
*
* @param clazz
* The class of the object that was originally encoded into
* Value.
*
* @param context
* An arbitrary object that can optionally be supplied by the
* application to convey an application-specific context for the
* operation. (See {@link CoderContext}.) The default value is
* null.
*
* @throws ConversionException
*/
public void render(Value value, Object target, Class clazz, CoderContext context) throws ConversionException;
}