OUr goal for today

Basic operations

• Users have to be logged in to place bids
• Users place bids on items (highest bid wins)
• Bids from other users are visible automatically

task: index page should return properly - with OK (HTTP 200)

task: define the LOGIN page (route, action, view)

views & templates

• Scala-based template engine
• plain HTML(5)
• the magic '@' character

task: REnder a template on the login page

hint: the action renders the view

Template engine: REVERSE Lookup

• Retrieves URL for a controller's action from routes file
• @routes.<Controller>.<Action>

<a href="@routes.Application.index()">Home</a>
<!-- yields: <a href="/">... -->

task: Add a link in the login page pointing to the home page

Global error handling

• Override the methods which you need

public class ErrorHandler extends DefaultHttpErrorHandler {
  // Execute default error handling
  @Inject
  public ErrorHandler(Configuration configuration, Environment environment, OptionalSourceMapper sourceMapper, Provider<Router> routes) {
    super(configuration, environment, sourceMapper, routes);
  }

  // Override page not found behavior
  @Override
  protected Promise<Result> onNotFound(Http.RequestHeader requestHeader, String s) {
    return Promise.pure(badRequest(
      views.html.notFound.render(requestHeader.uri())));
  }
}

Global error handling

Place your ErrorHandler in the project's root or register it in the application.conf

play.http.errorHandler = "my.own.ErrorHandler"

task: DEFINE a Custom error handler (only for 404 requests)

Forms

task: render an html login form at the login page

• username and password fields
• think about the action URL

Form submission handling I

// bind the form to the data coming from the request
DynamicForm dynamicForm = Form.form().bindFromRequest();
// extract single fields
String username = dynamicForm.get("username");
                                   ^-- matches the name of the HTML field

task: handle login form submission (route, action)

form data validation

task: basic form data  validation

Form submission handling II

public static final Form<LoginData> loginForm = Form.form(LoginData.class);

Form<LoginData> submittedForm = loginForm.bindFromRequest();
if (submittedForm.hasErrors()) {
    return badRequest("Username and password validation failed.");
} else {
    String username = submittedForm.get().getUsername();
    return ok("Hello, " + username);
}

Play data validation constraints

• @Required
• @MinLength(...)
• @Email
• See Constraints

task: proper form data  validation

• Required fields
• Minimum length
• Proper validation message

form helpers

task: enhance form handling

• Username preserved even if there was a validation error
• Show the validation errors along with the form

Sessions

overview

• Signed cookies

  • application.secret key in application.conf is used
• Cookie is part of HTTP header

operations on cookies

session().clear();

session("someKey");

session().remove("someKey");

session("someKey", someValue);

Think "Map"

Action composition

a.k.a. Action Chaining

Action composition

@Security.Authenticated(Secured.class)
public Result index() {
  return ok(views.html.index.render());
}

Action composition

import play.mvc.*;
import play.mvc.Http.*;

public class Secured extends Security.Authenticator {
  @Override
  public String getUsername(Context ctx) {
    return ctx.session().get("username");
  }

  @Override
  public Result onUnauthorized(Context ctx) {
    return redirect(routes.Application.login());
  }
}

task: session handling

• Secure the index page
• Redirect to login page if no session present
• Show the username in the index page if user is logged in
• Implement a logout action

web Services

http get

import play.libs.ws.*;
import static play.libs.F.Promise;

WSRequest request = WS.url("http://google.com");
Promise<WSResponse> promiseResponse = request.get();
//NOTICE:                            HTTP GET ^

customizing WSRequest

WSRequest request =
  WS.url("http://google.com")
    .setRequestTimeout(1000)
    .setQueryParameter("q", "Play Framework");

http post

import play.libs.ws.*;
import static play.libs.F.Promise;

Promise<WSResponse> promiseResponse =
  WS.url("http://example.com")
    .setContentType("application/x-www-form-urlencoded")
    .post("param1=value1");

Retrieve response (blocking)

import play.libs.ws.*;
import java.util.concurrent.TimeUnit;
import static play.libs.F.Promise;

Promise<WSResponse> promiseResponse =
  WS.url("http://google.com").get();

WSResponse response = promiseResponse.get(10, TimeUnit.SECONDS);
//             ^^ Blocks thread until service responds

task: Authenticate via web services

• No more hard-coded validation
• Auth against http://devbay-auth.herokuapp.com
• Make a POST request to /auth with the credentials (urlFormEncoded)
• Wait for the response and react properly:
  • 200 - OK, return null
  • other - NOT OK, return "Wrong credentials"

json

handling json request

public Result auth() {
    JsonNode json = request().body().asJson();
    if (json==null) {
        return badRequest("Oh, I actually expected JSON data");
    } else {
        // happy path
    }
}

// or even better

@BodyParser.Of(BodyParser.Json.class)
public Result auth() {
    JsonNode json = request().body().asJson();
}

serving json response

public Result sayHello() {
    ObjectNode result = Json.newObject();
    result.put("exampleField1", "foobar");
    result.put("exampleField2", "Hello world!");
    return ok(result);
}

task: authentication with json data via web service

• Rewrite the authentication check to send JSON data instead of form data.
• Examine the "status" field in the returned JSON object

models

ebean orm

https://ebean-orm.github.io/

ebean orm in play

project/plugins.sbt

build.sbt

lazy val myProject = (project in file(".")).enablePlugins(PlayJava, PlayEbean)

addSbtPlugin("com.typesafe.sbt" % "sbt-play-ebean" % "1.0.0")

conf/application.conf

ebean.default = ["models.*"]

task: DEFINE a model for representing items to bid on

Quiz: what happens when Evolutions are enabled and we change the model?

scheduling async tasks

(with Akka)

// given an ActorSystem system

system.scheduler().scheduleOnce(
    Duration.create(10, TimeUnit.MILLISECONDS),
    () -> file.delete(), // Runnable object here
    system.dispatcher()
);

task: populate the database with initial data - when the application controller is initialized

task: render all items on the index page

task: render a template which serves another page with html and angularjs markup

"server sends [...] to connected clients and clients reply"

task: define A Websocket-endpoint (route, action)

angularjs

• data binding

• directives

• backend

group task: examine the javascript code

who handles the Websocket connection?

akka in 30 seconds

• Akka
• Actor system
• Actors
• Messages

actors in java (not that fun as in scala)

public class HelloActorProtocol {

    public static class SayHello {
        public final String name;

        public SayHello(String name) {
            this.name = name;
        }
    }
}


import akka.actor.*;

public class HelloActor extends UntypedActor {

    public static Props props = Props.create(HelloActor.class);

    public void onReceive(Object msg) throws Exception {
        if (msg instanceof SayHello) {
            sender().tell("Hello, " + ((SayHello) msg).name, self());
        }
    }
}

actors in scala (more fun)

import akka.actor._

object HelloActor {
  def props = Props[HelloActor]
  
  case class SayHello(name: String)
}

class HelloActor extends Actor {
  import HelloActor._
  
  def receive = {
    case SayHello(name: String) =>
      sender() ! "Hello, " + name
  }
}

task: define an actor for handling the websocket connection