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SKILL.mdplugins/developer-kit-java/skills/aws-sdk-java-v2-dynamodb/

name:
aws-sdk-java-v2-dynamodb
description:
Provides Amazon DynamoDB patterns using AWS SDK for Java 2.x. Use when creating, querying, scanning, or performing CRUD operations on DynamoDB tables, working with indexes, batch operations, transactions, or integrating with Spring Boot applications.
allowed-tools:
Read, Write, Edit, Bash, Glob, Grep

AWS SDK for Java 2.x - Amazon DynamoDB

Overview

Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability. This skill covers patterns for working with DynamoDB using AWS SDK for Java 2.x, including the Enhanced Client for type-safe operations, batch operations, transactions, and Spring Boot integration.

When to Use

Use this skill when:

  • Creating, updating, or deleting DynamoDB tables
  • Performing CRUD operations on DynamoDB items
  • Querying or scanning tables
  • Working with Global Secondary Indexes (GSI) or Local Secondary Indexes (LSI)
  • Implementing batch operations for efficiency
  • Using DynamoDB transactions
  • Integrating DynamoDB with Spring Boot applications
  • Working with DynamoDB Enhanced Client for type-safe operations

Instructions

Follow these steps to work with Amazon DynamoDB:

  1. Add Dependencies - Include dynamodb and dynamodb-enhanced dependencies
  2. Create Client - Instantiate DynamoDbEnhancedClient for type-safe operations
  3. Define Entities - Annotate classes with @DynamoDbBean for mapping
  4. Configure Tables - Set up DynamoDbTable instances for your entities
  5. CRUD Operations - Implement putItem, getItem, updateItem, deleteItem
  6. Query Operations - Use QueryConditional for filtered queries
  7. Batch Operations - Use batchGetItem and batchWriteItem for efficiency
  8. Test Locally - Use LocalStack or DynamoDB Local for development

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

To define DynamoDB entities, use @DynamoDbBean annotation:

@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

// 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

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

customers.forEach(batchBuilder::addPutItem);

enhancedClient.batchWriteItem(r -> r.addWriteBatch(batchBuilder.build()));

Transactions

Transactional Write

enhancedClient.transactWriteItems(r -> r
    .addPutItem(customerTable, customer)
    .addPutItem(orderTable, order));

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

  1. Use Enhanced Client: Provides type-safe operations with less boilerplate
  2. Design partition keys carefully: Distribute data evenly across partitions
  3. Use composite keys: Leverage sort keys for efficient queries
  4. Create GSIs strategically: Support different access patterns
  5. Use batch operations: Reduce API calls for multiple items
  6. Implement pagination: For large result sets use pagination
  7. Use transactions: For operations that must be atomic
  8. Avoid scans: Prefer queries with proper indexes
  9. Handle conditional writes: Prevent race conditions
  10. Use proper error handling: Handle exceptions like ProvisionedThroughputExceeded

Examples

Example 1: 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 List<User> findByEmail(String email) {
        Expression filter = Expression.builder()
            .expression("email = :email")
            .putExpressionValue(":email",
                AttributeValue.builder().s(email).build())
            .build();

        return userTable.scan(r -> r.filterExpression(filter))
            .items().stream()
            .collect(Collectors.toList());
    }

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

Example 2: 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
    }
}

Example 3: Transaction Write

public void placeOrder(Order order, Customer customer) {
    enhancedClient.transactWriteItems(r -> r
        .addPutItem(orderTable, order)
        .addUpdateItem(customerTable,
            UpdateItem.builder()
                .key(Key.builder().partitionValue(customer.getId()).build())
                .updateExpression("ADD orderCount :one")
                .expressionValues(Map.of(":one",
                    AttributeValue.builder().n("1").build()))
                .build()));
}

Common Patterns

Conditional Operations

PutItemEnhancedRequest request = PutItemEnhancedRequest.builder(table)
    .item(customer)
    .conditionExpression("attribute_not_exists(customerId)")
    .build();

table.putItemWithRequestBuilder(request);

Pagination

ScanEnhancedRequest request = ScanEnhancedRequest.builder()
    .limit(100)
    .build();

PaginatedScanIterable<Customer> results = table.scan(request);
results.stream().forEach(page -> {
    // Process each page
});

Performance Considerations

  • Monitor read/write capacity units
  • Implement exponential backoff for retries
  • Use proper pagination for large datasets
  • Consider eventual consistency for reads
  • Use ReturnConsumedCapacity to monitor capacity usage

Related Skills

  • aws-sdk-java-v2-core - Core AWS SDK patterns
  • spring-data-jpa - Alternative data access patterns
  • unit-test-service-layer - Service testing patterns
  • unit-test-wiremock-rest-api - Testing external APIs

Constraints and Warnings

  • Item Size Limit: DynamoDB items are limited to 400KB
  • Partition Key Design: Poor partition key design causes hot partitions
  • Read/Write Capacity: Monitor consumed capacity to avoid throttling
  • Eventual Consistency: Eventually consistent reads may return stale data
  • Scan Operations: Scans consume large amounts of read capacity; avoid when possible
  • Batch Limits: Batch operations are limited to 25 or 100 items
  • Transaction Costs: Transactions cost 2x the read/write capacity units
  • Index Limit: Tables can have up to 5 GSI and 5 LSI
  • TTL Costs: Time-to-live deletion still consumes write capacity
  • Global Tables: Multi-region replication increases costs significantly

References

  • AWS DynamoDB Documentation
  • AWS SDK for Java Documentation
  • DynamoDB Examples
  • LocalStack for Testing

For detailed implementations, see the references folder:

plugins

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skills

aws-sdk-java-v2-dynamodb

SKILL.md

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