DynamoDB Streams 低级 API：Java 示例

注意

本页上的代码并不详尽，不会处理使用 Amazon DynamoDB Streams 的所有场景。建议利用 Kinesis Client Library (KCL) 通过 Amazon Kinesis Adapter 使用 DynamoDB 中的流记录，如 使用 DynamoDB Streams Kinesis Adapter 处理流记录 中所述。

本节包含一个演示 DynamoDB Streams 的实际运用的 Java 程序。此程序执行以下操作：

1. 创建一个启用了流的 DynamoDB 表。

2. 描述此表的流设置。

3. 修改表中的数据。

4. 描述流中的分片。

5. 从分片中读取流记录。

6. 清理。

当您运行此程序时，将显示与以下内容类似的输出。

Issuing CreateTable request for TestTableForStreams
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: 01234567890...,},}
    Shard iterator: EjYFEkX2a26eVTWe...
        ApproximateCreationDateTime: Tue Mar 20 09:50:00 PDT 2018,Keys: {Id={N: 1,}},NewImage: {Message={S: New item!,}, Id={N: 1,}},SequenceNumber: 100000000003218256368,SizeBytes: 24,StreamViewType: NEW_AND_OLD_IMAGES}
         {ApproximateCreationDateTime: Tue Mar 20 09:50:00 PDT 2018,Keys: {Id={N: 1,}},NewImage: {Message={S: This item has changed,}, Id={N: 1,}},OldImage: {Message={S: New item!,}, Id={N: 1,}},SequenceNumber: 200000000003218256412,SizeBytes: 56,StreamViewType: NEW_AND_OLD_IMAGES}
         {ApproximateCreationDateTime: Tue Mar 20 09:50:00 PDT 2018,Keys: {Id={N: 1,}},OldImage: {Message={S: This item has changed,}, Id={N: 1,}},SequenceNumber: 300000000003218256413,SizeBytes: 36,StreamViewType: NEW_AND_OLD_IMAGES}
...
Deleting the table...
Demo complete

例

package com.amazon.codesamples;

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

import com.amazonaws.AmazonClientException;
import com.amazonaws.auth.DefaultAWSCredentialsProviderChain;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBStreams;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBStreamsClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeAction;
import com.amazonaws.services.dynamodbv2.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.AttributeValueUpdate;
import com.amazonaws.services.dynamodbv2.model.CreateTableRequest;
import com.amazonaws.services.dynamodbv2.model.DescribeStreamRequest;
import com.amazonaws.services.dynamodbv2.model.DescribeStreamResult;
import com.amazonaws.services.dynamodbv2.model.DescribeTableResult;
import com.amazonaws.services.dynamodbv2.model.GetRecordsRequest;
import com.amazonaws.services.dynamodbv2.model.GetRecordsResult;
import com.amazonaws.services.dynamodbv2.model.GetShardIteratorRequest;
import com.amazonaws.services.dynamodbv2.model.GetShardIteratorResult;
import com.amazonaws.services.dynamodbv2.model.KeySchemaElement;
import com.amazonaws.services.dynamodbv2.model.KeyType;
import com.amazonaws.services.dynamodbv2.model.ProvisionedThroughput;
import com.amazonaws.services.dynamodbv2.model.Record;
import com.amazonaws.services.dynamodbv2.model.Shard;
import com.amazonaws.services.dynamodbv2.model.ShardIteratorType;
import com.amazonaws.services.dynamodbv2.model.StreamSpecification;
import com.amazonaws.services.dynamodbv2.model.StreamViewType;
import com.amazonaws.services.dynamodbv2.util.TableUtils;

public class StreamsLowLevelDemo {

        public static void main(String args[]) throws InterruptedException {

                AmazonDynamoDB dynamoDBClient = AmazonDynamoDBClientBuilder
                                .standard()
                                .withRegion(Regions.US_EAST_2)
                                .withCredentials(new DefaultAWSCredentialsProviderChain())
                                .build();

                AmazonDynamoDBStreams streamsClient = AmazonDynamoDBStreamsClientBuilder
                                .standard()
                                .withRegion(Regions.US_EAST_2)
                                .withCredentials(new DefaultAWSCredentialsProviderChain())
                                .build();

                // Create a table, with a stream enabled
                String tableName = "TestTableForStreams";

                ArrayList<AttributeDefinition> attributeDefinitions = new ArrayList<>(
                                Arrays.asList(new AttributeDefinition()
                                                .withAttributeName("Id")
                                                .withAttributeType("N")));

                ArrayList<KeySchemaElement> keySchema = new ArrayList<>(
                                Arrays.asList(new KeySchemaElement()
                                                .withAttributeName("Id")
                                                .withKeyType(KeyType.HASH))); // Partition key

                StreamSpecification streamSpecification = new StreamSpecification()
                                .withStreamEnabled(true)
                                .withStreamViewType(StreamViewType.NEW_AND_OLD_IMAGES);

                CreateTableRequest createTableRequest = new CreateTableRequest().withTableName(tableName)
                                .withKeySchema(keySchema).withAttributeDefinitions(attributeDefinitions)
                                .withProvisionedThroughput(new ProvisionedThroughput()
                                                .withReadCapacityUnits(10L)
                                                .withWriteCapacityUnits(10L))
                                .withStreamSpecification(streamSpecification);

                System.out.println("Issuing CreateTable request for " + tableName);
                dynamoDBClient.createTable(createTableRequest);
                System.out.println("Waiting for " + tableName + " to be created...");

                try {
                        TableUtils.waitUntilActive(dynamoDBClient, tableName);
                } catch (AmazonClientException e) {
                        e.printStackTrace();
                }

                // Print the stream settings for the table
                DescribeTableResult describeTableResult = dynamoDBClient.describeTable(tableName);
                String streamArn = describeTableResult.getTable().getLatestStreamArn();
                System.out.println("Current stream ARN for " + tableName + ": " +
                                describeTableResult.getTable().getLatestStreamArn());
                StreamSpecification streamSpec = describeTableResult.getTable().getStreamSpecification();
                System.out.println("Stream enabled: " + streamSpec.getStreamEnabled());
                System.out.println("Update view type: " + streamSpec.getStreamViewType());
                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
                        Map<String, AttributeValue> item = new HashMap<>();
                        item.put("Id", new AttributeValue().withN(i.toString()));
                        item.put("Message", new AttributeValue().withS("New item!"));
                        dynamoDBClient.putItem(tableName, item);

                        // Update the item
                        Map<String, AttributeValue> key = new HashMap<>();
                        key.put("Id", new AttributeValue().withN(i.toString()));
                        Map<String, AttributeValueUpdate> attributeUpdates = new HashMap<>();
                        attributeUpdates.put("Message", new AttributeValueUpdate()
                                        .withAction(AttributeAction.PUT)
                                        .withValue(new AttributeValue()
                                                        .withS("This item has changed")));
                        dynamoDBClient.updateItem(tableName, key, attributeUpdates);

                        // Delete the item
                        dynamoDBClient.deleteItem(tableName, key);
                }

                // Get all the shard IDs from the stream. Note that DescribeStream returns
                // the shard IDs one page at a time.
                String lastEvaluatedShardId = null;

                do {
                        DescribeStreamResult describeStreamResult = streamsClient.describeStream(
                                        new DescribeStreamRequest()
                                                        .withStreamArn(streamArn)
                                                        .withExclusiveStartShardId(lastEvaluatedShardId));
                        List<Shard> shards = describeStreamResult.getStreamDescription().getShards();

                        // Process each shard on this page

                        for (Shard shard : shards) {
                                String shardId = shard.getShardId();
                                System.out.println("Shard: " + shard);

                                // Get an iterator for the current shard

                                GetShardIteratorRequest getShardIteratorRequest = new GetShardIteratorRequest()
                                                .withStreamArn(streamArn)
                                                .withShardId(shardId)
                                                .withShardIteratorType(ShardIteratorType.TRIM_HORIZON);
                                GetShardIteratorResult getShardIteratorResult = streamsClient
                                                .getShardIterator(getShardIteratorRequest);
                                String currentShardIter = getShardIteratorResult.getShardIterator();

                                // Shard iterator is not null until the Shard is sealed (marked as READ_ONLY).
                                // To prevent running the loop until the Shard is sealed, which will be on
                                // average
                                // 4 hours, we process only the items that were written into DynamoDB and then
                                // exit.
                                int processedRecordCount = 0;
                                while (currentShardIter != null && processedRecordCount < maxItemCount) {
                                        System.out.println("    Shard iterator: " + currentShardIter.substring(380));

                                        // Use the shard iterator to read the stream records

                                        GetRecordsResult getRecordsResult = streamsClient
                                                        .getRecords(new GetRecordsRequest()
                                                                        .withShardIterator(currentShardIter));
                                        List<Record> records = getRecordsResult.getRecords();
                                        for (Record record : records) {
                                                System.out.println("        " + record.getDynamodb());
                                        }
                                        processedRecordCount += records.size();
                                        currentShardIter = getRecordsResult.getNextShardIterator();
                                }
                        }

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

                } while (lastEvaluatedShardId != null);

                // Delete the table
                System.out.println("Deleting the table...");
                dynamoDBClient.deleteTable(tableName);

                System.out.println("Demo complete");

        }
}