DynamoDB-Streams-Low-Level-API: Java-Beispiel

Anmerkung

Der Code auf dieser Seite ist nicht umfassend und behandelt nicht alle Szenarien für die Nutzung von Amazon DynamoDB Streams. Die empfohlene Methode für die Nutzung von Stream-Datensätzen aus DynamoDB erfolgt anhand des Amazon-Kinesis-Adapters unter Verwendung der Kinesis-Client-Library (KCL) gemäß der Beschreibung in Verwenden des DynamoDB-Streams-Kinesis-Adapters zum Verarbeiten von Stream-Datensätzen.

Dieser Abschnitt enthält ein Java-Programm, das DynamoDB Streams in Aktion zeigt. Das Programm führt Folgendes aus:

1. Erstellt eine DynamoDB-Tabelle mit einem aktivierten Stream.

2. Beschreibt die Stream-Einstellungen für diese Tabelle.

3. Ändert die Daten in der Tabelle.

4. Beschreibt die Shards im Stream.

5. Liest die Stream-Datensätze aus den Shards.

6. Ruft untergeordnete Shards ab und liest weiter Datensätze.

7. Bereinigt die Daten.

Wenn Sie das Programm ausführen, wird eine Ausgabe ähnlich der folgenden angezeigt.

Testing Streams Demo
Creating an Amazon DynamoDB table TestTableForStreams with a simple primary key: Id
Waiting for TestTableForStreams to be created...
Current stream ARN for TestTableForStreams: arn:aws:dynamodb:us-east-2:123456789012:table/TestTableForStreams/stream/2018-03-20T16:49:55.208
Stream enabled: true
Update view type: NEW_AND_OLD_IMAGES

Performing write activities on TestTableForStreams
Processing item 1 of 100
Processing item 2 of 100
Processing item 3 of 100
...
Processing item 100 of 100
Shard: {ShardId: shardId-1234567890-...,SequenceNumberRange: {StartingSequenceNumber: 100002572486797508907,},}
    Shard iterator: EjYFEkX2a26eVTWe...
        StreamRecord(ApproximateCreationDateTime=2025-04-09T13:11:58Z, Keys={Id=AttributeValue(S=4)}, NewImage={Message=AttributeValue(S=New Item!), Id=AttributeValue(S=4)}, SequenceNumber=2000001584047545833909, SizeBytes=22, StreamViewType=NEW_AND_OLD_IMAGES)
        StreamRecord(ApproximateCreationDateTime=2025-04-09T13:11:58Z, Keys={Id=AttributeValue(S=4)}, NewImage={Message=AttributeValue(S=This is an updated item), Id=AttributeValue(S=4)}, OldImage={Message=AttributeValue(S=New Item!), Id=AttributeValue(S=4)}, SequenceNumber=2100003604869767892701, SizeBytes=55, StreamViewType=NEW_AND_OLD_IMAGES)
        StreamRecord(ApproximateCreationDateTime=2025-04-09T13:11:58Z, Keys={Id=AttributeValue(S=4)}, OldImage={Message=AttributeValue(S=This is an updated item), Id=AttributeValue(S=4)}, SequenceNumber=2200001099771112898434, SizeBytes=36, StreamViewType=NEW_AND_OLD_IMAGES)
...
Deleting the table...
Table StreamsDemoTable deleted.
Demo complete

Beispiel

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import software.amazon.awssdk.core.waiters.WaiterResponse;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeAction;
import software.amazon.awssdk.services.dynamodb.model.AttributeDefinition;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.AttributeValueUpdate;
import software.amazon.awssdk.services.dynamodb.model.BillingMode;
import software.amazon.awssdk.services.dynamodb.model.CreateTableRequest;
import software.amazon.awssdk.services.dynamodb.model.CreateTableResponse;
import software.amazon.awssdk.services.dynamodb.model.DeleteItemRequest;
import software.amazon.awssdk.services.dynamodb.model.DeleteTableRequest;
import software.amazon.awssdk.services.dynamodb.model.DescribeStreamRequest;
import software.amazon.awssdk.services.dynamodb.model.DescribeStreamResponse;
import software.amazon.awssdk.services.dynamodb.model.DescribeTableRequest;
import software.amazon.awssdk.services.dynamodb.model.DescribeTableResponse;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.model.GetRecordsRequest;
import software.amazon.awssdk.services.dynamodb.model.GetRecordsResponse;
import software.amazon.awssdk.services.dynamodb.model.GetShardIteratorRequest;
import software.amazon.awssdk.services.dynamodb.model.GetShardIteratorResponse;
import software.amazon.awssdk.services.dynamodb.model.KeySchemaElement;
import software.amazon.awssdk.services.dynamodb.model.KeyType;
import software.amazon.awssdk.services.dynamodb.model.PutItemRequest;
import software.amazon.awssdk.services.dynamodb.model.Record;
import software.amazon.awssdk.services.dynamodb.model.ScalarAttributeType;
import software.amazon.awssdk.services.dynamodb.model.Shard;
import software.amazon.awssdk.services.dynamodb.model.ShardFilter;
import software.amazon.awssdk.services.dynamodb.model.ShardFilterType;
import software.amazon.awssdk.services.dynamodb.model.ShardIteratorType;
import software.amazon.awssdk.services.dynamodb.model.StreamSpecification;
import software.amazon.awssdk.services.dynamodb.model.TableDescription;
import software.amazon.awssdk.services.dynamodb.model.UpdateItemRequest;
import software.amazon.awssdk.services.dynamodb.streams.DynamoDbStreamsClient;
import software.amazon.awssdk.services.dynamodb.waiters.DynamoDbWaiter;

public class StreamsLowLevelDemo {


    public static void main(String[] args) {
        final String usage = "Testing Streams Demo";
        try {
            System.out.println(usage);

            String tableName = "StreamsDemoTable";
            String key = "Id";
            System.out.println("Creating an Amazon DynamoDB table " + tableName + " with a simple primary key: " + key);
            Region region = Region.US_WEST_2;
            DynamoDbClient ddb = DynamoDbClient.builder()
                    .region(region)
                    .build();

            DynamoDbStreamsClient ddbStreams = DynamoDbStreamsClient.builder()
                    .region(region)
                    .build();
            DescribeTableRequest describeTableRequest = DescribeTableRequest.builder()
                    .tableName(tableName)
                    .build();
            TableDescription tableDescription = null;
            try{
                tableDescription = ddb.describeTable(describeTableRequest).table();
            }catch (Exception e){
                System.out.println("Table " + tableName + " does not exist.");
                tableDescription = createTable(ddb, tableName, key);
            }

            // Print the stream settings for the table
            String streamArn = tableDescription.latestStreamArn();
           
            StreamSpecification streamSpec = tableDescription.streamSpecification();
            System.out.println("Current stream ARN for " + tableDescription.tableName() + ": " +
                   streamArn);
            System.out.println("Stream enabled: " + streamSpec.streamEnabled());
            System.out.println("Update view type: " + streamSpec.streamViewType());
            System.out.println();
            // Generate write activity in the table
            System.out.println("Performing write activities on " + tableName);
            int maxItemCount = 100;
            for (Integer i = 1; i <= maxItemCount; i++) {
                System.out.println("Processing item " + i + " of " + maxItemCount);
                // Write a new item
                putItemInTable(key, i, tableName, ddb);
                // Update the item
                updateItemInTable(key, i, tableName, ddb);
                // Delete the item
                deleteDynamoDBItem(key, i, tableName, ddb);
            }

            // Process Stream
            processStream(streamArn, maxItemCount, ddb, ddbStreams, tableName);

            // Delete the table
            System.out.println("Deleting the table...");
            DeleteTableRequest deleteTableRequest = DeleteTableRequest.builder()
                    .tableName(tableName)
                    .build();
            ddb.deleteTable(deleteTableRequest);
            System.out.println("Table " + tableName + " deleted.");
            System.out.println("Demo complete");
            ddb.close();
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    }

    private static void processStream(String streamArn, int maxItemCount, DynamoDbClient ddb, DynamoDbStreamsClient ddbStreams, String tableName) {
        // Get all the shard IDs from the stream. Note that DescribeStream returns
        // the shard IDs one page at a time.
        String lastEvaluatedShardId = null;
        do {
            DescribeStreamRequest describeStreamRequest = DescribeStreamRequest.builder()
                    .streamArn(streamArn)
                    .exclusiveStartShardId(lastEvaluatedShardId).build();
            DescribeStreamResponse describeStreamResponse = ddbStreams.describeStream(describeStreamRequest);

            List<Shard> shards = describeStreamResponse.streamDescription().shards();

            // Process each shard on this page

            fetchShardsAndReadRecords(streamArn, maxItemCount, ddbStreams, shards);

            // If LastEvaluatedShardId is set, then there is
            // at least one more page of shard IDs to retrieve
            lastEvaluatedShardId = describeStreamResponse.streamDescription().lastEvaluatedShardId();

        } while (lastEvaluatedShardId != null);

    }

    private static void fetchShardsAndReadRecords(String streamArn, int maxItemCount, DynamoDbStreamsClient ddbStreams, List<Shard> shards) {
        for (Shard shard : shards) {
            String shardId = shard.shardId();
            System.out.println("Shard: " + shard);

            // Get an iterator for the current shard
            GetShardIteratorRequest shardIteratorRequest = GetShardIteratorRequest.builder()
                    .streamArn(streamArn).shardId(shardId)
                    .shardIteratorType(ShardIteratorType.TRIM_HORIZON).build();

            GetShardIteratorResponse getShardIteratorResult = ddbStreams.getShardIterator(shardIteratorRequest);

            String currentShardIter = getShardIteratorResult.shardIterator();

            // Shard iterator is not null until the Shard is sealed (marked as READ_ONLY).
            // To prevent running the loop until the Shard is sealed, we process only the
            // items that were written into DynamoDB and then exit.
            int processedRecordCount = 0;
            while (currentShardIter != null && processedRecordCount < maxItemCount) {
                // Use the shard iterator to read the stream records
                GetRecordsRequest getRecordsRequest = GetRecordsRequest.builder()
                        .shardIterator(currentShardIter).build();
                GetRecordsResponse getRecordsResult = ddbStreams.getRecords(getRecordsRequest);
                List<Record> records = getRecordsResult.records();
                for (Record record : records) {
                    System.out.println("        " + record.dynamodb());
                }
                processedRecordCount += records.size();
                currentShardIter = getRecordsResult.nextShardIterator();
            }
            if (currentShardIter == null){
                System.out.println("Shard has been fully processed. Shard iterator is null.");
                System.out.println("Fetch the child shard to continue processing instead of bulk fetching all shards");
                DescribeStreamRequest describeStreamRequestForChildShards = DescribeStreamRequest.builder()
                        .streamArn(streamArn)
                        .shardFilter(ShardFilter.builder()
                                .type(ShardFilterType.CHILD_SHARDS)
                                .shardId(shardId).build())
                        .build();
                DescribeStreamResponse describeStreamResponseChildShards = ddbStreams.describeStream(describeStreamRequestForChildShards);
                fetchShardsAndReadRecords(streamArn, maxItemCount, ddbStreams, describeStreamResponseChildShards.streamDescription().shards());
            }
        }
    }

    private static void putItemInTable(String key, Integer i, String tableName, DynamoDbClient ddb) {
        Map<String, AttributeValue> item = new HashMap<>();
        item.put(key, AttributeValue.builder()
                .s(i.toString())
                .build());
        item.put("Message", AttributeValue.builder()
                .s("New Item!")
                .build());
        PutItemRequest request = PutItemRequest.builder()
                .tableName(tableName)
                .item(item)
                .build();
        ddb.putItem(request);
    }

    private static void updateItemInTable(String key, Integer i, String tableName, DynamoDbClient ddb) {

        HashMap<String, AttributeValue> itemKey = new HashMap<>();
        itemKey.put(key, AttributeValue.builder()
                .s(i.toString())
                .build());


        HashMap<String, AttributeValueUpdate> updatedValues = new HashMap<>();
        updatedValues.put("Message", AttributeValueUpdate.builder()
                .value(AttributeValue.builder().s("This is an updated item").build())
                .action(AttributeAction.PUT)
                .build());

        UpdateItemRequest request = UpdateItemRequest.builder()
                .tableName(tableName)
                .key(itemKey)
                .attributeUpdates(updatedValues)
                .build();
        ddb.updateItem(request);
    }

    public static void deleteDynamoDBItem(String key, Integer i, String tableName, DynamoDbClient ddb) {
        HashMap<String, AttributeValue> keyToGet = new HashMap<>();
        keyToGet.put(key, AttributeValue.builder()
                .s(i.toString())
                .build());

        DeleteItemRequest deleteReq = DeleteItemRequest.builder()
                .tableName(tableName)
                .key(keyToGet)
                .build();
        ddb.deleteItem(deleteReq);
    }

    public static TableDescription createTable(DynamoDbClient ddb, String tableName, String key) {
        DynamoDbWaiter dbWaiter = ddb.waiter();
        StreamSpecification streamSpecification = StreamSpecification.builder()
                .streamEnabled(true)
                .streamViewType("NEW_AND_OLD_IMAGES")
                .build();
        CreateTableRequest request = CreateTableRequest.builder()
                .attributeDefinitions(AttributeDefinition.builder()
                        .attributeName(key)
                        .attributeType(ScalarAttributeType.S)
                        .build())
                .keySchema(KeySchemaElement.builder()
                        .attributeName(key)
                        .keyType(KeyType.HASH)
                        .build())
                .billingMode(BillingMode.PAY_PER_REQUEST) //  DynamoDB automatically scales based on traffic.
                .tableName(tableName)
                .streamSpecification(streamSpecification)
                .build();

        TableDescription newTable;
        try {
            CreateTableResponse response = ddb.createTable(request);
            DescribeTableRequest tableRequest = DescribeTableRequest.builder()
                    .tableName(tableName)
                    .build();
                    
            System.out.println("Waiting for " + tableName + " to be created...");

            // Wait until the Amazon DynamoDB table is created.
            WaiterResponse<DescribeTableResponse> waiterResponse = dbWaiter.waitUntilTableExists(tableRequest);
            waiterResponse.matched().response().ifPresent(System.out::println);
            newTable = response.tableDescription();
            return newTable;

        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
        return null;
    }



}