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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2016-2016 Amazon.com, 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://aws.amazon.com/apache2.0
 *
 * This file 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.amazonaws.services.dynamodbv2.datamodeling;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Date;

/**
 * Annotation for marking a property as auto-generatable.
 *
 * A minimal example using getter annotations,
 *  * @DynamoDBTable(tableName="TestTable")
 * public class TestClass {
 *     private String key;
 *     private Date createdDate;
 *     private Date lastUpdatedDate;
 *
 *     @DynamoDBHashKey
 *     public String getKey() { return key; }
 *     public void setKey(String key) { this.key = key; }
 *
 *     @DynamoDBAutoGeneratedTimestamp(strategy=DynamoDBAutoGenerateStrategy.CREATE)
 *     public Date getCreatedDate() { return createdDate; }
 *     public void setCreatedDate(Date createdDate) { this.createdDate = createdDate; }
 *
 *     @DynamoDBAutoGeneratedTimestamp(strategy=DynamoDBAutoGenerateStrategy.ALWAYS)
 *     public Date getLastUpdatedDate() { return lastUpdatedDate; }
 *     public void setLastUpdatedDate(Date lastUpdatedDate) { this.lastUpdatedDate = lastUpdatedDate; }
 * }
 * 
 *
 * Please note,
 *
 * Only {@link java.util.Calendar}, {@link java.util.Date} and {@link Long} are
 * supported for now. Primitives such as {@code long} are not supported since
 * the unset (or null) state can't be detected.
 *
 * @see com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAutoGenerateStrategy
 */
@DynamoDBAutoGenerated(generator=DynamoDBAutoGeneratedTimestamp.Generator.class)
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface DynamoDBAutoGeneratedTimestamp {

    /**
     * The auto-generation strategy; default is {@code ALWAYS}.
     * @see com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAutoGenerateStrategy
     */
    DynamoDBAutoGenerateStrategy strategy() default DynamoDBAutoGenerateStrategy.ALWAYS;

    /**
     * Default generator.
     */
    static final class Generator implements DynamoDBAutoGenerator {
        private final DynamoDBTypeConverter converter;
        private final DynamoDBAutoGenerateStrategy strategy;

        public Generator(final Class targetType, final DynamoDBAutoGeneratedTimestamp annotation) {
            this.converter = StandardTypeConverters.Scalar.DATE.getConverter(targetType);
            this.strategy = annotation.strategy();
        }

        @Override
        public final DynamoDBAutoGenerateStrategy getGenerateStrategy() {
            return strategy;
        }

        @Override
        public final T generate(final T currentValue) {
            return converter.unconvert(new Date());
        }
    }

}