低级别接口

每个语言特定 Amazon SDK 为 Amazon DynamoDB 提供了一个低级别接口，其方法与低级别 DynamoDB API 请求非常相似。

在某些情况下，您需要使用 数据类型描述符 识别数据类型，例如 S 对于字符串，N 对于数字。

下面的 Java 程序使用低级别 Amazon SDK for Java 接口。程序对 Music 表中的歌曲发出 GetItem 请求，并打印该歌曲的发行年份。

com.amazonaws.services.dynamodbv2.AmazonDynamoDB 类实施 DynamoDB 低级接口。

package com.amazonaws.codesamples;

import java.util.HashMap;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.GetItemRequest;
import com.amazonaws.services.dynamodbv2.model.GetItemResult;

public class MusicLowLevelDemo {

    public static void main(String[] args) {

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

        HashMap<String, AttributeValue> key = new HashMap<String, AttributeValue>();
        key.put("Artist", new AttributeValue().withS("No One You Know"));
        key.put("SongTitle", new AttributeValue().withS("Call Me Today"));

        GetItemRequest request = new GetItemRequest()
            .withTableName("Music")
            .withKey(key);

        try {
            GetItemResult result = client.getItem(request);
            if (result && result.getItem() != null) {
                AttributeValue year = result.getItem().get("Year");
                System.out.println("The song was released in " + year.getN());
            } else {
                System.out.println("No matching song was found");
            }
        } catch (Exception e) {
            System.err.println("Unable to retrieve data: ");
            System.err.println(e.getMessage());
        }
    }
}