Play

Question 1

As at 2016 what was the only full-stack reactive web application framework for the JVM

Answer 1

play

Question 2

Play is built on top of _______ and leverages its reactive behaviour by using __________

Answer 2

Netty

Asynchronous stream handling

Question 3

Play deals with the typical concerns of web application development such as client- side resource handling, project compilation, and packaging by making use of

Answer 3

the sbt build tool

Question 4

They have certainly evolved a lot over the past decades, especially in terms of CPU clock speed (MHz to GHz) and memory (kilobytes to gigabytes). The most significant change, however, which has happened in the past few years, is that although the clock speed of CPUs isn’t increasing very much, the

Answer 4

the number of cores each CPU has is changing

Question 5

what is the von Neumann bottleneck

Answer 5

There is a shared bus between the program memory and data memory leads to the von Neumann bottleneck.
Because the single bus can only access one of the two classes of memory at a time, throughput is lower than the rate at which the CPU can work.

Question 6

Roughly speaking, there are two categories of programming models in which web serv- ers can be placed.

Answer 6

Threaded

Evented

Question 7

The threaded model

Answer 7

large numbers of threads take care of handling the incoming requests.

Question 8

The evented model

Answer 8

a small number of request-processing threads communicate with each other through message passing.

Question 9

Example of a threaded server

Answer 9

Apache Tomcat, IIS

Question 10

The evented model only works if

Answer 10

the entire pipeline is asynchronous

Question 11

What is the architectural challenge you seek to address with Actors and Events

Answer 11

Developing web applications fit for multicore architectures

Question 12

Languages and tools favoring the use of ______ _______make it easier to develop web applications that have to deal with concurrent access.

Answer 12

immutable state

Question 13

Building applications that don’t fail is extremely difficult, and if those applications are meant to be built at a reasonable pace it’s close to impossible. Instead of avoiding failure, reactive systems are designed and built from the ground up to embrace failure, leveraging the principle of

Answer 13

supervision

Question 14

What are the 8 fallacies of distributed computing

Answer 14

1 The network is reliable
2 Latency is zero
3 Bandwidth is infinite
4 The network is secure
5 Topology doesn’t change
6 There is one administrator
7 Transport cost is zero
8 The network is homogeneous

Question 15

What is an iteratee

Answer 15

An iteratee is a construct that allows you to consume streams of data asynchronously; it’s one of the cornerstones of the Play Framework.

Question 16

The counterpart of an iteratee is

Answer 16

an enumerator

Question 17

Just as the iteratee is an ____________, the enumerator is an ____________

Answer 17

asynchronous consumer of data,

asynchronous producer of data:

Question 18

A component that lets you transform streaming data on the fly, called an

Answer 18

enumeratee

Question 19

An Enumeratee[From, To] does what

Answer 19

takes chunks of type From from an enumerator and transforms them into chunks of type To.

Question 20

How is using an Enumeratee different from using java.io.Inputstream and java.io.outputstream?

Answer 20

iteratees let you manipulate streams of data asynchronously. In prac- tice, this means that these streams won’t hold on to a thread in the absence of new data.
java.io.OutputStream blocks the thread it’s using until new data is available.

Question 21

What is the The iteratee the enumerator and enumeratee in the fawcet analogy

Answer 21

The enumerator is the fawcet
The Enumeratee is the nozzel of the fawcet
The iteratee is the class that receives the flow of water

Question 22

What is the collective term for iteratees, enumerators and enumeratees

Answer 22

Reactive streams

Question 23

What is set to replace iteratees in the next release of Play

Answer 23

Akka streams

Question 24

What are web sockets

Answer 24

is an advanced technology that makes it possible to open an interactive (full duplex) communication session between the user’s browser and a server. With this API, you can send messages to a server and receive event-driven responses without having to poll the server for a reply.

Question 25

Play’s WebSocket handling mechanism is built around

Answer 25

Akka streams

Question 26

play.extras.iteratees.Encoding.decode does what

Answer 26

decode a stream of bytes as a UTF-8 string.

Question 27

play.extras.iteratees.JsonIteratees.jsSimpleObject

Answer 27

parse a single JSON object.

Question 28

play.api.libs.iteratee.Enumeratee.grouped

Answer 28

will apply the jsSimpleObject iteratee over and over again until the stream is finished.

Question 29

what is needed for sbt to correctly run a play app

Answer 29

Play needs to be imported in both the

build. sbt (or build.scala) file as well as the
plugins. sbt file

Question 30

the _______________file is the page we will be able to see when we run our application

Answer 30

The views/main.scala.html file is the page we will be able to see when we run our application

Question 31

why the file is named main.scala.html and not main.html

Answer 31

because it is a twirl template

Question 32

what is the syntax to start a new play project using activator

Answer 32

activator new play-scala

Question 33

conf/messages ?

Answer 33

this is where all of the default messages are stored (you could then have a messages file for every other localisation e.g. conf/messages.en-us (for english)

Question 34

The I18nSupport trait gives you

Answer 34

an implicit Messages value as long as there is a Lang or a RequestHeader in the implicit scope.

Question 35

play.api.i18n.I18nSupport
play.i18n.I18nSupport
what is the difference?

Answer 35

the .api is reserved for scala, otherwise it is Java

Question 36

dependency injection

Answer 36

a technique whereby one object supplies the dependencies of another object

Question 37

In dependency injection passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern.

This fundamental requirement means that

Answer 37

using values (services) produced within the class from new or static methods is prohibited

Question 38

Twirl templates can be generated as a class rather than a static object by

Answer 38

declaring a constructor using a special @this(args) syntax at the top of the template.

Question 39

Default dependency injection framework for Play

Answer 39

Guice