View.html.index cannot be resolved to a type

If your play project in eclipse says that it can't resolve a type (see message below), but you are certain that everything should be fine

$ View.html.index cannot be resolved to a type

try to make a clean compile

$ activator clean compile eclipse

It helped me to resolve my issue.

Kill Play Framework process

When we run application in DEV mode (using command activator run) the process normally will be killed when terminal is closed. It's pretty easy since PID is started/closed automatically and therefore we do not care about it at all.

Once we start application in PROD mode there is a file RUNNING_PID is created (./target/universal/stage/RUNNING_PID). There is a command (since version 2.4) in activator (stopProd) which will close PID

$ activator stopProd

Alternatively you can just kill process 'manually'

$ kill $(cat target/universal/stage/RUNNING_PID)

Play Framework project in production - Building process

We want to deploy our Play project to production environment.

Create a binary version of application

There are two commands that can help you to make a build. Simply run dist (it invokes universal:packageBin) or universal:packageZipTarball in Play console and wait

$ dist

$ universal:packageZipTarball

Result will be a ZIP or TGZ file located in target/universal folder with everything needed for you project (it means you do not need to install SBT or Activator on your server, just pure Java). Once you extract ZIP you will find 2 runner files in bin folder (one for unix and one for windows). Just run it and your server will up

$ path/to/hellow-world/bin/hello-world-app 
[info] play.api.Play - Application started (Prod)
[info] p.c.s.NettyServer - Listening for HTTP on /0:0:0:0:0:0:0:0:9000

Make sure you have rights to run server, sometimes you need to give rights (see example below)

$ chmod +x /path/to/bin/project-name

To run process in background

$ sudo nohup target/universal/stage/bin/eqa-app -Dhttp.port=80 -Dplay.crypto.secret="secret_token_123" /dev/null 2>&1 &

Play Framework project in production - Application Secret

I am going to make series of articles about how to deploy Play Framework (version 2.5) application on centOS together with build system Jenkins. I'm doing this first time and want to document everything for myself and at the same time I hope it can be useful for somebody else as well.

Before I wrote few articles how to setup hello-world project on centOS or macOS however now I'm going to work on production setup. I assume you already have you hello-world project and clean centOS environment.

Let's have a look on important moment.

Application secret

Each play application has secret key which is used for signing session and some other important stuff. It is not possible to run play project in production mode in case if secret is not set or if it is set to default value 'changeme'. Secret key is stored in application.conf file /path/to/hello-word/conf/application.conf in variable play.crypto.secret (see below).

## Secret key
# http://www.playframework.com/documentation/latest/ApplicationSecret
# ~~~~~
# The secret key is used to sign Play's session cookie.
# This must be changed for production, but we don't recommend you change it in this file.
play.crypto.secret = "changeme"

Of course we should not share our secret key and therefore it has to be used/stored on production side only.

There are at least 3 ways how we can use secret key on production side.

1. Secret key as a parameter

It is fine if you have simple application on 1 server, but I would not really recommend that for bigger project.

/path/to/hello-world -Dplay.crypto.secret="secret_token_123"

2. Environment variables

That would read variable from OS environment, otherwise default value will be used (actually the last defined one, in example below it is "chagneme").

play.crypto.secret="changeme"
play.crypto.secret=${?APPLICATION_SECRET}

3. Use separate configuration file

Separate configuration is probably the best way to go.

include "application"
play.crypto.secret="QCY?tAnfk?aZ?iwrNwnxIlR6CTf:G3gf:90Latabg@5241AB`R5W:1uDFN];Ik@n"

They include config while running application.

/path/to/hello-word/bin/yourapp -Dconfig.file=/path/to/production.conf

Secret tools

There are few already builtin function that can help you deal with secrets: playGenerateSecret (generate secret) and playUpdateSecret (generate and update into config).

$ playGenerateSecret
[info] Generated new secret: G28Dze]Z4lr@Or_9DCoz;tT_yCj6opKkkIh27K>[0l_NT9lZaFfs?=zx[Wulz>cX
[success] Total time: 0 s, completed Jan 11, 2017 6:24:12 PM

$ playUpdateSecret
[info] Generated new secret: QmJ?udauJgDj34AYifbprJvbT5I8^Vw1MY0WmbYRscZmAOotkalbhXbIs^48_Uc9
[info] Updating application secret in /Users/dpa/git/eqa-app/conf/application.conf
[info] Replacing old application secret: changeme
[success] Total time: 0 s, completed Jan 11, 2017 9:22:06 PM

HTTP Routing in Play Framework

We are going to check how Play connect http requests with our code. F.x. when user hits http://localhost:9000/ what happens?

HTTP Routing

There is already built in http router in Play Framework. It allows to connect incoming requests with Play Action and therefore with public method in a controller class.

Configuring HTTP Routing

Normally the configuration for HTTP routing is located in conf/routes. See example:

# Static path
GET   /clients/all                  controllers.Clients.list()
# Dynamic path
GET   /clients/:id                  controllers.Clients.show(id: Long)
GET   /files/*name               controllers.Application.download(name)
# Dynamic parts with regexp
GET   /items/$id<[0-9]+>    controllers.Items.show(id: Long)

If there are few routes are matched for the same request then the first one in a configuration file will be used.

Template literals

I have to follow up with changes to ES6. Today I noticed template literals (there is also tagged template literals but that I will check later).
I am really happy with that, it is simple and helps a lot.

Template literals are a new feature in ES6 that provide us string template things!

Let's have a look on real example

var a = "Apples";
var b = 10;
console.log(`I would like to buy ${b+b} ${a}.`);
// I would like to buy 20 Apples.

Actions in Play Framework 2.5

Requests that come to application based on Play usually are processed by thing which is called action.

Action it is just a method that processes parameters of requests and sends result back to web client

Let's look on example below

package controllers;

import play.mvc.*;

/**
 * This controller contains an action to handle HTTP requests
 * to the application's home page.
 */
public class HomeController extends Controller {

    /**
     * An action that renders an HTML page with a welcome message.
     * The configuration in the routes file means that
     * this method will be called when the application receives a
     * GET request with a path of /.
     */
    public Result index() {
        return ok("Hello World!");
    }

}

We see an action index that return Result (HTTP response which we send to web client).

Hello World on Play Framework 2.5 on OSX

Today we are going to make Hello World project based on Play Framework 2.5 on OS X

I'm getting back to Play Framework again and I'm going to build simple start project.

1. Checking if Java is installed

Make sure you have java installed.

java -version

If java is installed you will see message like that:

java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

2. Installing Typesafe activator (current version is 1.3.12)

brew install typesafe-activator

3. Let's create a new project

activator new hello-world

Activator will ask you what template you want to use for new project? (I used play-java).

  1) minimal-akka-java-seed
  2) minimal-akka-scala-seed
  3) minimal-java
  4) minimal-scala
  5) play-java
  6) play-scala

That will create a java project for us

Now let's run it. Go into newly create project and run activator

activator run

That will run our project and up server as well. You can access project by localhost:9000

Programming Pascal's triangle

What is Pascal's triangle?

It is a triangular array which is consists from binomial coefficients (you can see visual representation of it below).

To get more information check article on wiki: Pascal's triangle.

I had a task where I needed to find out a value in a cell and what I only had were coordinates of it. I came with quit simple solution (Scala) which I really like.

The idea is to move up from the initial cell to the borders (left and right, since I know the values there) and once I am there, I move back to my initial cell but now I can bring some values from above.

object Main {
  def main(args: Array[String]) {    
    println(pascal(4, 3))
  }

  def pascal(c: Int, r: Int): Int = {
    if (c == 0 || r == 0 || c == r) 1
    else pascal(c - 1, r - 1) + pascal(c, r - 1)
  }
}