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Async Rest Client to DynamoDB using Spring Boot

1. Overview

Starting from Spring framework 5.0 and Spring Boot 2.0, the framework provides support for asynchronous programming, so does AWS SDK starting with 2.0 version.

In this post i will be exploring using asynchronous DynamoDB API and Spring Webflux by building simple reactive REST application. Let’s say we need to handle HTTP requests for retrieving or storing some Event(id:string, body: string). Event will be stored in DynamoDB.

It might be easier to simply look at the code on Github and follow it there.

2. Dependencies

Let’s start with Maven dependencies for WebFlux and DynamoDB SDK


3. DynamoDB

3.1 Spring Configuration

A simple config were we set up connection to DynamoDB. For test purpose we need to specify dynamoEndpoint and forreal application we need to specify aws region.

public class AppConfig {
    String accessKey;

    String secretKey;

    String dynamoEndpoint;

    AwsBasicCredentials awsBasicCredentials(){
        return AwsBasicCredentials.create(accessKey, secretKey);

    DynamoDbAsyncClient dynamoDbAsyncClient(AwsBasicCredentials awsBasicCredentials){
        DynamoDbAsyncClientBuilder clientBuilder = DynamoDbAsyncClient.builder();

application.yaml with connection details

  accessKey: any
  secretKey: any
  endpoint: http://localhost:8000/

3.2 Reactive DynamoDB Service

Unfortunately, second version of AWS SDK doesn’t have support for DynamoDBMapper yet(you can track mapper’s readiness here), so table creation, sending requests and parsing responses need to be done by “low level” API.

In DynamoDbService we gonna:

  • Create table if its not exists
  • Implement methods for saving and retrieving event
public class DynamoDbService {

    public static final String TABLE_NAME = "events";
    public static final String ID_COLUMN = "id";
    public static final String BODY_COLUMN = "body";

    final DynamoDbAsyncClient client;

    public DynamoDbService(DynamoDbAsyncClient client) {
        this.client = client;

    //Creating table on startup if not exists
    public void createTableIfNeeded() throws ExecutionException, InterruptedException {
        ListTablesRequest request = ListTablesRequest.builder().exclusiveStartTableName(TABLE_NAME).build();
        CompletableFuture<ListTablesResponse> listTableResponse = client.listTables(request);

        CompletableFuture<CreateTableResponse> createTableRequest = listTableResponse
                .thenCompose(response -> {
                    boolean tableExist = response.tableNames().contains(TABLE_NAME);
                    if (!tableExist) {
                        return createTable();
                    } else {
                        return CompletableFuture.completedFuture(null);

        //Wait in synchronous manner for table creation

    public CompletableFuture<PutItemResponse> saveEvent(Event event) {
        Map<String, AttributeValue> item = new HashMap<>();
        item.put(ID_COLUMN, AttributeValue.builder().s(event.getUuid()).build());
        item.put(BODY_COLUMN, AttributeValue.builder().s(event.getBody()).build());

        PutItemRequest putItemRequest = PutItemRequest.builder()

        return client.putItem(putItemRequest);

    public CompletableFuture<Event> getEvent(String id) {
        Map<String, AttributeValue> key = new HashMap<>();
        key.put(ID_COLUMN, AttributeValue.builder().s(id).build());

        GetItemRequest getRequest = GetItemRequest.builder()

        return client.getItem(getRequest).thenApply(item -> {
            if (!item.hasItem()) {
                return null;
            } else {
                Map<String, AttributeValue> itemAttr = item.item();
                String body = itemAttr.get(BODY_COLUMN).s();
                return new Event(id, body);

    private CompletableFuture<CreateTableResponse> createTable() {

        CreateTableRequest request = CreateTableRequest.builder()


        return client.createTable(request);

4. Reactive REST Controller

A simple controller with GET method for retrieving event by id and POST method for saving events in DynamoDB. We can do it in two ways - implement it with annotations or get rid of annotations and do it in functional way.There is no performance impact, in almost most cases it is absolutely based on individual preference what to use.

4.1 Annotated Controllers
public class AnnotatedController {

    final DynamoDbService dynamoDbService;

    public AnnotatedController(DynamoDbService dynamoDbService) {
        this.dynamoDbService = dynamoDbService;

    @GetMapping(value = "/{eventId}", produces = MediaType.APPLICATION_JSON_VALUE)
    public Mono<Event> getEvent(@PathVariable String eventId) {
        CompletableFuture<Event> eventFuture = dynamoDbService.getEvent(eventId);
        return Mono.fromCompletionStage(eventFuture);

    @PostMapping(consumes = MediaType.APPLICATION_JSON_VALUE)
    public void saveEvent(@RequestBody Event event) {

4.2 Functional Endpoints

This is a lightweight functional programming model in which functions are used to route and handle requests.

public class HttpRouter {

    public RouterFunction<ServerResponse> eventRouter(DynamoDbService dynamoDbService) {
        EventHandler eventHandler = new EventHandler(dynamoDbService);
        return RouterFunctions
                        .and(accept(APPLICATION_JSON)), eventHandler::getEvent)
                        .and(contentType(APPLICATION_JSON)), eventHandler::saveEvent);

    static class EventHandler {
        private final DynamoDbService dynamoDbService;

        public EventHandler(DynamoDbService dynamoDbService) {
            this.dynamoDbService = dynamoDbService;

        Mono<ServerResponse> getEvent(ServerRequest request) {
            String eventId = request.pathVariable("id");
            CompletableFuture<Event> eventGetFuture = dynamoDbService.getEvent(eventId);
            Mono<Event> eventMono = Mono.fromFuture(eventGetFuture);
            return ServerResponse.ok().body(eventMono, Event.class);

        Mono<ServerResponse> saveEvent(ServerRequest request) {
            Mono<Event> eventMono = request.bodyToMono(Event.class);
            return ServerResponse.ok().build();

5. Spring DynamoDB Integration Test

5.1 Maven dependencies

For running integration test with DynamoDB we need DynamoDBLocal, which is not really the DynamoDB, but SQLite withimplemented DynamoDB interfaces on top of it.


                        <!--Keen an eye on output directory - it will be used for starting dynamodb-->

        <name>DynamoDB Local Release Repository</name>

5.2 DynamoDB server

Now we need to start DynamoDB before test run. I prefer to do it as JUnit Class Rule, but we can also do it as a spring bean.

public class LocalDynamoDbRule extends ExternalResource {

    protected DynamoDBProxyServer server;

    public LocalDynamoDbRule() {
        //here we set the path from "outputDirectory" of maven-dependency-plugin
        System.setProperty("sqlite4java.library.path", "target/native-libs");

    protected void before() throws Exception {
        this.server = ServerRunner
            .createServerFromCommandLineArgs(new String[]{"-inMemory", "-port", "8000"});

    protected void after() {

    protected void stopUnchecked(DynamoDBProxyServer dynamoDbServer) {
        try {
        } catch (Exception e) {
            throw new RuntimeException(e);

5.3 Running test

Now we can create an integration test and test get event by id and save event.

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class IntegrationTest {

    public static LocalDynamoDbRule dynamoDbRule = new LocalDynamoDbRule();

    private WebTestClient webTestClient;

    public void getEvent() {
        // Create a GET request to test an endpoint
                // and use the dedicated DSL to test assertions against the response

    public void saveEvent() throws InterruptedException {
        Event event = new Event("10", "event");

6. Docker

Here we gonna prepare our application for running in docker, so it will be ready for deploying to AWS.

Small hint: starting from Java 10 you can specify how much memory JVM will use depending on container memory.
-XX:MaxRAMPercentage=75.0 means JVM won't use more then 75% of a container memory.

# Use our standard java12 baseimage
FROM openjdk:12-alpine

# Copy the artifact into the container
COPY target/dynamodb-spring-*-exec.jar /srv/service.jar

# Run the artifact and expose the default port

ENTRYPOINT [ "java", \
    "-XX:+UnlockExperimentalVMOptions", \
    "-XX:+ExitOnOutOfMemoryError", \
    "-XX:MaxRAMPercentage=75.0", \
    "", \
    "-jar", "service.jar", \
    "" ]


Building the docker container itself docker build -t spring-dynamo .
Also let's see what was generated by sudo docker image ls

REPOSITORY          TAG                 IMAGE ID            CREATED              SIZE
spring-dynamo       latest              a974d880400e        About a minute ago   364MB
openjdk             12-alpine           0c68e7c5b7a0        12 months ago        339MB

Finally, our poc is ready!

Happy coding :)

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