对象持久化接口

如果不直接执行数据层面操作，一些 Amazon SDK 提供对象持久化接口。相反，您可以创建表示 Amazon DynamoDB 表和索引中项目的对象，并且仅与这些对象进行交互。这允许您编写以对象为中心的代码，而不是以数据库为中心的代码。

以下 Java 程序使用 DynamoDBMapper，Amazon SDK for Java 的对象持久化接口。MusicItem 类表示 Music 表的项目。

package com.amazonaws.codesamples;

import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBRangeKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;

@DynamoDBTable(tableName="Music")
public class MusicItem {
    private String artist;
    private String songTitle;
    private String albumTitle;
    private int year;

    @DynamoDBHashKey(attributeName="Artist")
    public String getArtist() { return artist;}
    public void setArtist(String artist) {this.artist = artist;}

    @DynamoDBRangeKey(attributeName="SongTitle")
    public String getSongTitle() { return songTitle;}
    public void setSongTitle(String songTitle) {this.songTitle = songTitle;}

    @DynamoDBAttribute(attributeName = "AlbumTitle")
    public String getAlbumTitle() { return albumTitle;}
    public void setAlbumTitle(String albumTitle) {this.albumTitle = albumTitle;}

    @DynamoDBAttribute(attributeName = "Year")
    public int getYear() { return year; }
    public void setYear(int year) { this.year = year; }
}

然后，您可以实例化 MusicItem 对象，然后使用 DynamoDBMapper 的 load() 方法。然后，该程序打印该歌曲的发行年份。

com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper 类实施 DynamoDB 对象持久化接口。注意DynamoDBMapper充当一个围绕低级别客户端的包装程序 (AmazonDynamoDB)。

package com.amazonaws.codesamples;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;


public class MusicMapperDemo {

    public static void main(String[] args) {

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

        DynamoDBMapper mapper = new DynamoDBMapper(client);

        MusicItem keySchema = new MusicItem();
        keySchema.setArtist("No One You Know");
        keySchema.setSongTitle("Call Me Today");

        try {
            MusicItem result = mapper.load(keySchema);
            if (result != null) {
                System.out.println(
                "The song was released in "+ result.getYear());
            } else {
                System.out.println("No matching song was found");
            }
        } catch (Exception e) {
            System.err.println("Unable to retrieve data: ");
            System.err.println(e.getMessage());
        }

    }

}