aws-sdk-java-v2-dynamodb

SKILL.md

AWS SDK for Java 2.x - Amazon DynamoDB

Overview

Provides DynamoDB patterns using AWS SDK for Java 2.x with Enhanced Client for type-safe CRUD, queries, batch operations, transactions, and Spring Boot integration.

When to Use

CRUD operations on DynamoDB items

Querying tables with sort keys or GSI

Batch operations for multiple items

Atomic transactions across tables

Spring Boot integration with DynamoDB

Instructions

Add AWS SDK DynamoDB dependencies to pom.xml

Configure client setup (low-level or Enhanced Client)

Define entity classes with @DynamoDbBean annotations

Perform operations using DynamoDbTable (CRUD, query, scan, batch, transactions)

Handle partial failures with retry logic and exponential backoff

Use repository pattern for Spring Boot integration

Dependencies

Add to pom.xml:

<!-- Low-level DynamoDB client -->
<dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>dynamodb</artifactId>
</dependency>

<!-- Enhanced client (recommended) -->
<dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>dynamodb-enhanced</artifactId>
</dependency>

Client Setup

Low-Level Client

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;

DynamoDbClient dynamoDb = DynamoDbClient.builder()
    .region(Region.US_EAST_1)
    .build();

Enhanced Client (Recommended)

import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClient;

DynamoDbEnhancedClient enhancedClient = DynamoDbEnhancedClient.builder()
    .dynamoDbClient(dynamoDb)
    .build();

Entity Mapping

@DynamoDbBean
public class Customer {

    @DynamoDbPartitionKey
    private String customerId;

    @DynamoDbAttribute("customer_name")
    private String name;

    private String email;

    @DynamoDbSortKey
    private String orderId;

    // Getters and setters
}

For complex entity mapping with GSIs and custom converters, see Entity Mapping Reference.

CRUD Operations

Basic Operations

// Create or update item
DynamoDbTable<Customer> table = enhancedClient.table("Customers", TableSchema.fromBean(Customer.class));
table.putItem(customer);

// Get item
Customer result = table.getItem(Key.builder().partitionValue(customerId).build());

// Update item
return table.updateItem(customer);

// Delete item
table.deleteItem(Key.builder().partitionValue(customerId).build());

Composite Key Operations

// Get item with composite key
Order order = table.getItem(Key.builder()
    .partitionValue(customerId)
    .sortValue(orderId)
    .build());

Query Operations

Basic Query

import software.amazon.awssdk.enhanced.dynamodb.model.QueryConditional;

QueryConditional queryConditional = QueryConditional
    .keyEqualTo(Key.builder()
        .partitionValue(customerId)
        .build());

List<Order> orders = table.query(queryConditional).items().stream()
    .collect(Collectors.toList());

Advanced Query with Filters

import software.amazon.awssdk.enhanced.dynamodb.Expression;

Expression filter = Expression.builder()
    .expression("status = :pending")
    .putExpressionValue(":pending", AttributeValue.builder().s("PENDING").build())
    .build();

List<Order> pendingOrders = table.query(r -> r
    .queryConditional(queryConditional)
    .filterExpression(filter))
    .items().stream()
    .collect(Collectors.toList());

For detailed query patterns, see Advanced Operations Reference.

Scan Operations

Warning: Scan reads entire table and consumes read capacity for all items. Prefer Query operations with partition keys or GSIs whenever possible.

Validation before scan:

Confirm query with partition key is not feasible for your access pattern

Verify table has sufficient provisioned read capacity or use on-demand mode

Consider using pagination with limit() to control capacity consumption

// Scan all items
List<Customer> allCustomers = table.scan().items().stream()
    .collect(Collectors.toList());

// Scan with filter
Expression filter = Expression.builder()
    .expression("points >= :minPoints")
    .putExpressionValue(":minPoints", AttributeValue.builder().n("1000").build())
    .build();

List<Customer> vipCustomers = table.scan(r -> r.filterExpression(filter))
    .items().stream()
    .collect(Collectors.toList());

Batch Operations

Batch Get

import software.amazon.awssdk.enhanced.dynamodb.model.*;

List<Key> keys = customerIds.stream()
    .map(id -> Key.builder().partitionValue(id).build())
    .collect(Collectors.toList());

ReadBatch.Builder<Customer> batchBuilder = ReadBatch.builder(Customer.class)
    .mappedTableResource(table);

keys.forEach(batchBuilder::addGetItem);

BatchGetResultPageIterable result = enhancedClient.batchGetItem(r ->
    r.addReadBatch(batchBuilder.build()));

List<Customer> customers = result.resultsForTable(table).stream()
    .collect(Collectors.toList());

Batch Write with Error Handling

WriteBatch.Builder<Customer> batchBuilder = WriteBatch.builder(Customer.class)
    .mappedTableResource(table);

customers.forEach(batchBuilder::addPutItem);

BatchWriteItemEnhancedRequest request = BatchWriteItemEnhancedRequest.builder()
    .addWriteBatch(batchBuilder.build())
    .build();

BatchWriteResult result = enhancedClient.batchWriteItem(request);

// Validate: check for unprocessed items
if (!result.writeResponsesForTable(table).isEmpty()) {
    // Retry unprocessed items with exponential backoff
    Map<String, AttributeValue> unprocessed = result.writeResponsesForTable(table).get(0)
        .unprocessedAttributes();
    if (unprocessed != null && !unprocessed.isEmpty()) {
        enhancedClient.batchWriteItem(r -> r
            .addWriteBatch(WriteBatch.builder(Customer.class)
                .mappedTableResource(table)
                .addPutItemFromItem(unprocessed)
                .build()));
    }
}

Transactions

Transactional Write with Retry

public void placeOrderWithRetry(Order order, Customer customer, int maxRetries) {
    int attempt = 0;
    while (attempt < maxRetries) {
        try {
            enhancedClient.transactWriteItems(r -> r
                .addPutItem(customerTable, customer)
                .addPutItem(orderTable, order));
            return;
        } catch (TransactionCanceledException e) {
            if (e.cancellationReasons().stream()
                .anyMatch(r -> r.code().equals("TransactionCanceledException")
                    && r.message().contains("throughput"))) {
                attempt++;
                if (attempt < maxRetries) {
                    try { Thread.sleep((long) Math.pow(2, attempt) * 100); }
                    catch (InterruptedException ie) { Thread.currentThread().interrupt(); }
                }
            } else {
                throw e; // Non-retryable error
            }
        }
    }
}

Transactional Read

TransactGetItemsEnhancedRequest request = TransactGetItemsEnhancedRequest.builder()
    .addGetItem(customerTable, customerKey)
    .addGetItem(orderTable, orderKey)
    .build();

List<Document> results = enhancedClient.transactGetItems(request);

Spring Boot Integration

Configuration

@Configuration
public class DynamoDbConfiguration {

    @Bean
    public DynamoDbClient dynamoDbClient() {
        return DynamoDbClient.builder()
            .region(Region.US_EAST_1)
            .build();
    }

    @Bean
    public DynamoDbEnhancedClient dynamoDbEnhancedClient(DynamoDbClient dynamoDbClient) {
        return DynamoDbEnhancedClient.builder()
            .dynamoDbClient(dynamoDbClient)
            .build();
    }
}

Repository Pattern

@Repository
public class CustomerRepository {

    private final DynamoDbTable<Customer> customerTable;

    public CustomerRepository(DynamoDbEnhancedClient enhancedClient) {
        this.customerTable = enhancedClient.table("Customers", TableSchema.fromBean(Customer.class));
    }

    public void save(Customer customer) {
        customerTable.putItem(customer);
    }

    public Optional<Customer> findById(String customerId) {
        Key key = Key.builder().partitionValue(customerId).build();
        return Optional.ofNullable(customerTable.getItem(key));
    }
}

For comprehensive Spring Boot integration patterns, see Spring Boot Integration Reference.

Testing

Unit Testing with Mocks

@ExtendWith(MockitoExtension.class)
class CustomerServiceTest {

    @Mock
    private DynamoDbClient dynamoDbClient;

    @Mock
    private DynamoDbEnhancedClient enhancedClient;

    @Mock
    private DynamoDbTable<Customer> customerTable;

    @InjectMocks
    private CustomerService customerService;

    @Test
    void saveCustomer_ShouldReturnSavedCustomer() {
        // Arrange
        when(enhancedClient.table(anyString(), any(TableSchema.class)))
            .thenReturn(customerTable);

        Customer customer = new Customer("123", "John Doe", "john@example.com");

        // Act
        Customer result = customerService.saveCustomer(customer);

        // Assert
        assertNotNull(result);
        verify(customerTable).putItem(customer);
    }
}

Integration Testing with LocalStack

@Testcontainers
@SpringBootTest
class DynamoDbIntegrationTest {

    @Container
    static LocalStackContainer localstack = new LocalStackContainer(
        DockerImageName.parse("localstack/localstack:3.0"))
        .withServices(LocalStackContainer.Service.DYNAMODB);

    @DynamicPropertySource
    static void configureProperties(DynamicPropertyRegistry registry) {
        registry.add("aws.endpoint",
            () -> localstack.getEndpointOverride(LocalStackContainer.Service.DYNAMODB).toString());
    }

    @Autowired
    private DynamoDbEnhancedClient enhancedClient;

    @Test
    void testCustomerCRUDOperations() {
        // Test implementation
    }
}

For detailed testing strategies, see Testing Strategies.

Best Practices

Use Enhanced Client: Type-safe operations with less boilerplate

Design partition keys for even distribution: Avoid hot partitions

Prefer queries over scans: Use GSIs for access patterns

Batch in chunks of 25/100: BatchGetItem limits to 100, BatchWriteItem to 25 per table

Handle partial failures: Implement retry with exponential backoff for ProvisionedThroughputExceeded

Use conditional writes: Prevent race conditions with attribute_not_exists(pk)

Examples

Complete CRUD Repository

@Repository
public class UserRepository {

    private final DynamoDbTable<User> userTable;

    public UserRepository(DynamoDbEnhancedClient enhancedClient) {
        this.userTable = enhancedClient.table("Users", TableSchema.fromBean(User.class));
    }

    public User save(User user) {
        userTable.putItem(user);
        return user;
    }

    public Optional<User> findById(String userId) {
        Key key = Key.builder().partitionValue(userId).build();
        return Optional.ofNullable(userTable.getItem(key));
    }

    public void deleteById(String userId) {
        userTable.deleteItem(Key.builder().partitionValue(userId).build());
    }
}

Conditional Write with Retry

public boolean createIfNotExists(User user) {
    PutItemEnhancedRequest<User> request = PutItemEnhancedRequest.builder(User.class)
        .item(user)
        .conditionExpression("attribute_not_exists(userId)")
        .build();

    try {
        userTable.putItemWithRequest(request);
        return true;
    } catch (ConditionalCheckFailedException e) {
        return false; // Item already exists
    }
}

Constraints and Warnings

Item Size Limit: DynamoDB items limited to 400KB

Partition Key Design: Poor design causes hot partitions

Batch Limits: BatchGetItem max 100, BatchWriteItem max 25 items per table

Transaction Costs: Transactions cost 2x read/write capacity units

Scan Operations: Scans consume large amounts of read capacity; use only when necessary

References

AWS DynamoDB Documentation

AWS SDK for Java Documentation

DynamoDB Examples

LocalStack for Testing

For detailed implementations, see the references folder:

Entity Mapping Reference

Advanced Operations Reference

Spring Boot Integration Reference

Testing Strategies