Overview

A Sample application built with Play framework, integrated with CosmosDB SQL API and a Rest service to demonstrate an end to end non-blocking application. The code base consists of two projects a REST API called PlayJavaRecommendationService and a Web App which depends on the REST API called PlayJavaReadingListWebApp.

Specifically, the following capabilities are demonstrated:

• Play 2.6 - Routing, Twirl templates, forms, Dependency Injection etc
• Akka HTTP server backend
• Calling REST APIs with Play WS
• Azure CosmosDB SQL API
• CosmosDB Async Java SDK
• RXJava Observable to CompletableFuture

Getting started

First:

• Java 8
• sbt
• Create a Cosmos DB collection for SQL API. Use "/reader" as the partition key.

Then:

• Update the following properties in application.cong for PlayJavaReadingListWebApp with your Cosmos DB connection information
  • endPoint
  • key
  • dataBase
  • collection
• sbt "run 9001" - from PlayJavaRecommendationService the to start the REST API
• sbt run - from PlayJavaReadingListWebApp to start the Web Application
• Access the WebApp at http://localhost:9000/

Highlights

CosmosDB Async Java SDK natively supports RxJava Observable but Java Play framework controller actions need CompletableFuture.The following function will convert a Observable to CompletableFuture

  private <T> CompletableFuture<T> toCompletableFuture(Observable<T> observable) {
    CompletableFuture<T> cf = new CompletableFuture();
    observable.single().subscribe(l -> cf.complete(l), l -> cf.completeExceptionally(l));
    return cf;
  }

In Play framework, action code must be non-blocking. So, the action must return a promise of the result immediately upon invocation. In java that would be an object of type CompletionStage. The following action function demonstrates combining two independent futures using thenCombine() and returning a CompletionStage which will eventually be redeemed by the view.

  public CompletionStage<Result> index() {
    CompletionStage<WSResponse> recommendationsCF = ws.url(config.getString("externalRestServices.recommendationService")).get();
    CompletableFuture<List<Document>> booksCF = dao.getReadersReadingListCompletableFuture("Tella");
    return recommendationsCF.thenCombineAsync(
        booksCF,
        (recommendations, books) -> {
          return ok(
              views.html.readingList.render(
                  convertToRecommendations(recommendations.asJson().toString()),
                  convertToBooks(books.toString())));
        },
        httpExecutionContext.current());
  }

Check out the source code for the Play Scala version of the appliation at PlayScala App. This app will require either CosmosDB Mongo API or Mongo DB

Check out the source code for the Spring Boot Web Flux version of the appliation at SpringBoot WebFlux App. This app will require either CosmosDB Mongo API or Mongo DB