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/*
* Copyright 2006-2010 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. All rights reserved.
*
* 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 com.amazon.carbonado.adapter;
import java.lang.annotation.*;
/**
* Allows annotations to be defined for supporting property types which are not
* natively supported by the underlying storage layer. Repositories must always
* attempt to match property types to the best matching native type, but they
* may have to rely on an adapter to make a conversion.
*
* <p>The annotation is just a pointer to an adapter implementation class. If
* the adapter class is not explicitly provided, it defaults to a static inner
* class named "Adapter" in the annotation itself.
*
* <p>The adapter class must have a public constructor that accepts the
* annotation that has the AdapterDefinition annotation. It must also define
* several adapt methods which convert property values. An adapt method needs
* to start with "adapt", accept one parameter and return something.
* <p>
* Example true/false adapter for booleans:
* <pre>
* @Documented
* <b>@Retention(RetentionPolicy.RUNTIME)</b>
* <b>@Target(ElementType.METHOD)</b>
* <b>@AdapterDefinition</b>
* public @interface TrueFalseAdapter {
*
* public static class Adapter {
* private final String propertyName;
*
* // Constructor may throw a MalformedTypeException if
* // params supplied by annotation are illegal.
*
* /**
* * @param type optional type of object that contains the adapted property
* * @param propertyName name of property with adapter
* * @param annotation specific annotation that binds to this adapter class
* */
* public Adapter(Class type, String propertyName, TrueFalseAdapter annotation) {
* this.propertyName = propertyName;
* }
*
* // Define at least two adapt methods for each supported property type.
*
* /**
* * @param propertyValue value to convert from
* */
* public char adaptToChar(boolean propertyValue) {
* return value ? 'T' : 'F';
* }
*
* /**
* * @param propertyValue value to convert from
* */
* public boolean adaptToBoolean(char propertyValue) {
* if (propertyValue == 'T') { return true; };
* if (propertyValue == 'F') { return false; };
* throw new IllegalArgumentException
* ("Cannot adapt '" + value + "' into boolean for property \"" +
* propertyName + '"');
* }
* }
* }
* </pre>
*
* The newly defined adapter can be applied to property accessors.
*
* <pre>
* public interface UserInfo extends Storable {
* <b>@TrueFalseAdapter</b>
* boolean isAdministrator();
* void setAdministrator(boolean admin);
* }
* </pre>
*
* @author Brian S O'Neill
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface AdapterDefinition {
/**
* Specify class which will perform property adaptation. Must have a public
* constructor with the signature
* <code>(Class type, String propertyName, <i>Annotation</i>)</code>,
* where <code><i>Annotation</i></code> refers to the annotation with the
* adapter definition.
*
* <p>The implementation class need not be explicitly specified. By
* default, the adapter class must be a static inner class of the
* annotation, named "Adapter".
*/
// Use void.class to mean default.
Class implementation() default void.class;
/**
* Optionally specify the set of preferred storage types for storing the
* adapted property, in order of most preferred to least preferred. A type
* in the set must be supported by the adapt methods to be considered.
*
* <p>If the repository is independent, it needs help on deciding exactly
* how to store the adapted property. A dependent repository will not have
* as much flexibility in selecting an appropriate type, but it may still
* need a hint.
*/
Class[] storageTypePreferences() default {};
}
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