【AWS】DynamoDB扫描操作获取表全部数据

Amazon DynamoDB 是一种完全托管的 NoSQL 数据库服务，提供快速且可预测的性能，同时还能够实现无缝扩展。使用 DynamoDB，您可以免除操作和扩展分布式数据库的管理工作负担，因而无需担心硬件预置、设置和配置、复制、软件修补或集群扩展等问题。DynamoDB 还提供静态加密，这消除了在保护敏感数据时涉及的操作负担和复杂性。

背景

有时需要将DynamoDB中的数据完全拷贝下来。需要用到扫描操作。

Amazon DynamoDB 中的 Scan 操作读取表或二级索引中的每个项目。默认情况下，Scan 操作返回表或索引中每个项目的全部数据属性。但是，单个 Scan 请求最多可检索 1 MB 数据。对于大表需要进行多次扫描操作。且需要注意的是读取限制，如果超出限制，那么就会告警。

我的表格结构如下

JAVA环境的配置 

（1）JDK和maven环境就不说了。

（2）将用户的认证相关内容放入配置文件当中，也可以直接写在代码当中（后面解决方法二就是直接写的）

（3）maven配置

因为用到了写入csv文件，因此引入了csv相关工具包。

<dependencyManagement><dependencies><dependency><groupId>com.amazonaws</groupId><artifactId>aws-java-sdk-bom</artifactId><version>1.11.327</version><type>pom</type><scope>import</scope></dependency></dependencies></dependencyManagement><dependencies><dependency><groupId>com.amazonaws</groupId><artifactId>aws-java-sdk-dynamodb</artifactId></dependency><dependency><groupId>net.sourceforge.javacsv</groupId><artifactId>javacsv</artifactId><version>2.0</version></dependency></dependencies>

解决方法（一）小容量读取

import com.amazonaws.auth.AWSCredentials; import com.amazonaws.auth.AWSStaticCredentialsProvider; import com.amazonaws.auth.PropertiesCredentials; 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.ScanRequest; import com.amazonaws.services.dynamodbv2.model.ScanResult;import java.io.File; import java.io.IOException; import java.util.List; import java.util.Map;public class DynamoDBUtils {public static void main(String[] args) throws IOException {AWSCredentials credentials = new PropertiesCredentials(new File("src/main/resources/key.properties"));AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().withCredentials(new AWSStaticCredentialsProvider(credentials)).withRegion("us-east-1").build();ScanRequest scanRequest = new ScanRequest().withTableName("yucheng");ScanResult result = client.scan(scanRequest);for (Map<String, AttributeValue> item : result.getItems()) {System.out.println(item);String query = item.get("query").getS();System.out.println(query);List<AttributeValue> asin_list = item.get("asin_list").getL();for (AttributeValue value : asin_list) {System.out.print(value.getS() + " ");}System.out.println();}} }

读取结果如下。

 解决方法（二）大容量读取

import com.amazonaws.auth.AWSCredentials; import com.amazonaws.auth.AWSStaticCredentialsProvider; import com.amazonaws.auth.BasicAWSCredentials; 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.ScanRequest; import com.amazonaws.services.dynamodbv2.model.ScanResult;import java.io.IOException; import java.nio.charset.Charset; import java.util.ArrayList;import java.util.List; import java.util.Map;import com.csvreader.CsvWriter;public class DynamoDBUtils {private static String region = "us-east-1";//替换成自己的private static String AWS_ACCESS_KEY_ID = "XXXXXX";//替换成自己的private static String AWS_SECRET_ACCESS_KEY = "XXXXXXXXXXX";//替换成自己的public static void main(String[] args) {try {f();} catch (InterruptedException | IOException e) {e.printStackTrace();}}public static void f() throws IOException, InterruptedException {String filePath = "XXXX.tsv";//替换成自己的AWSCredentials credentials = new BasicAWSCredentials(AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY);AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().withCredentials(new AWSStaticCredentialsProvider(credentials)).withRegion(region).build();CsvWriter csvWriter = new CsvWriter(filePath, '\t', Charset.forName("UTF-8"));int count = 0;Map<String, AttributeValue> lastKeyEvaluated = null;do {count++;if (count % 10 == 0) {System.out.println(count);}ScanRequest scanRequest = new ScanRequest().withTableName("yucheng").withExclusiveStartKey(lastKeyEvaluated);ScanResult result = client.scan(scanRequest);for (Map<String, AttributeValue> item : result.getItems()) {String query = item.get("query").getS();List<AttributeValue> asinList = item.get("asin_list").getL();List<String> asins = new ArrayList<>();for (AttributeValue value : asinList) {asins.add(value.getS());}String[] line = new String[2];line[0] = query;line[1] = String.join(",", asins);csvWriter.writeRecord(line);}lastKeyEvaluated = result.getLastEvaluatedKey();//为了控制频率，需要将此处进行一个暂停，不然DynamoDB承受不住就会告警Thread.sleep(40000);} while (lastKeyEvaluated != null);csvWriter.close();}}

 

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