A REST API showing Play with a JPA backend. For the Scala version, please see play-scala-rest-api-example in https://github.com/playframework/play-samples/.

If you look at the controller: PostController then you can see that when calling out to a blocking API like JDBC, you should put it behind an asynchronous boundary -- in practice, this means using the CompletionStage API to make sure that you're not blocking the rendering thread while the database call is going on in the background.

public CompletionStage<Result> list() {
    return handler.find().thenApplyAsync(posts -> {
        final List<PostResource> postList = posts.collect(Collectors.toList());
        return ok(Json.toJson(postList));
    }, ec.current());
}

There is more detail in https://www.playframework.com/documentation/latest/ThreadPools -- notably, you can always bump up the number of threads in the rendering thread pool rather than do this -- but it gives you an idea of best practices.

The best way to see what Play can do is to run a load test. We've included Gatling in this test project for integrated load testing.

Start Play in production mode, by staging the application and running the play script:s

sbt stage
cd target/universal/stage
./bin/play-java-rest-api-example -Dplay.http.secret.key=some-long-key-that-will-be-used-by-your-application

Then you'll start the Gatling load test up (it's already integrated into the project):

sbt ";project;gatling:test"

For best results, start the gatling load test up on another machine so you do not have contending resources. You can edit the Gatling simulation, and change the numbers as appropriate.

Once the test completes, you'll see an HTML file containing the load test chart, for example:

 ./play-java-rest-api-example/target/gatling/gatlingspec-1472579540405/index.html

That will contain your load test results.

By default, the project uses the Pekko HTTP Server backend. To switch to the Netty Server backend, enable the PlayNettyServer sbt plugin in the build.sbt file. In the build.sbt of this project, you'll find a commented line for this setting; simply uncomment it to make the switch. For more detailed information, refer to the Play Framework documentation.