示例：CRUD 操作

以下 Java 代码示例声明一个具有 Id、Title、ISBN 和 Authors 属性的 CatalogItem 类。它使用注释将这些属性映射到 DynamoDB 中的 ProductCatalog 表。然后，该示例使用 DynamoDBMapper 保存图书对象、对其进行检索和更新，并删除图书项目。

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 * Copyright 2010-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * This file is licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License. A copy of
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 *
 * http://aws.amazon.com/apache2.0/
 *
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 * specific language governing permissions and limitations under the License.
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package com.amazonaws.codesamples.datamodeling;

import java.io.IOException;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperConfig;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;

public class DynamoDBMapperCRUDExample {

    static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();

    public static void main(String[] args) throws IOException {
        testCRUDOperations();
        System.out.println("Example complete!");
    }

    @DynamoDBTable(tableName = "ProductCatalog")
    public static class CatalogItem {
        private Integer id;
        private String title;
        private String ISBN;
        private Set<String> bookAuthors;

        // Partition key
        @DynamoDBHashKey(attributeName = "Id")
        public Integer getId() {
            return id;
        }

        public void setId(Integer id) {
            this.id = id;
        }

        @DynamoDBAttribute(attributeName = "Title")
        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        @DynamoDBAttribute(attributeName = "ISBN")
        public String getISBN() {
            return ISBN;
        }

        public void setISBN(String ISBN) {
            this.ISBN = ISBN;
        }

        @DynamoDBAttribute(attributeName = "Authors")
        public Set<String> getBookAuthors() {
            return bookAuthors;
        }

        public void setBookAuthors(Set<String> bookAuthors) {
            this.bookAuthors = bookAuthors;
        }

        @Override
        public String toString() {
            return "Book [ISBN=" + ISBN + ", bookAuthors=" + bookAuthors + ", id=" + id + ", title=" + title + "]";
        }
    }

    private static void testCRUDOperations() {

        CatalogItem item = new CatalogItem();
        item.setId(601);
        item.setTitle("Book 601");
        item.setISBN("611-1111111111");
        item.setBookAuthors(new HashSet<String>(Arrays.asList("Author1", "Author2")));

        // Save the item (book).
        DynamoDBMapper mapper = new DynamoDBMapper(client);
        mapper.save(item);

        // Retrieve the item.
        CatalogItem itemRetrieved = mapper.load(CatalogItem.class, 601);
        System.out.println("Item retrieved:");
        System.out.println(itemRetrieved);

        // Update the item.
        itemRetrieved.setISBN("622-2222222222");
        itemRetrieved.setBookAuthors(new HashSet<String>(Arrays.asList("Author1", "Author3")));
        mapper.save(itemRetrieved);
        System.out.println("Item updated:");
        System.out.println(itemRetrieved);

        // Retrieve the updated item.
        DynamoDBMapperConfig config = DynamoDBMapperConfig.builder()
            .withConsistentReads(DynamoDBMapperConfig.ConsistentReads.CONSISTENT)
        .build();
        CatalogItem updatedItem = mapper.load(CatalogItem.class, 601, config);
        System.out.println("Retrieved the previously updated item:");
        System.out.println(updatedItem);

        // Delete the item.
        mapper.delete(updatedItem);

        // Try to retrieve deleted item.
        CatalogItem deletedItem = mapper.load(CatalogItem.class, updatedItem.getId(), config);
        if (deletedItem == null) {
            System.out.println("Done - Sample item is deleted.");
        }
    }
}