Play Framework

Front 1

What is JPDA ?

Back 1

The Java Platform Debugger Architecture (JPDA) provides the infrastructure you need to build end-user debugger applications for the Java Platform

Front 2

How to bnd an HTTP parameter to a Java method parameter?

Back 2

Just declare method parameters with the same name as the HTTP parameters.

Front 3

How to redirect to an action?

Back 3

Just call the corresponding Java method and play will generate the correct HTTP “Redirect” response.

public static void show(Long id) {
Article article = Article.findById(id);
render(article);
}


public static void edit(Long id, String title) {
Article article = Article.findById(id);
article.title = title;
article.save();
show(id);
}

Front 4

What is JPA?

Back 4

Java Persistence API

Persistence in this context covers three areas:

* the API itself, defined in the javax.persistence package
* the Java Persistence Query Language (JPQL)
* object/relational metadata

Front 5

What is REST?

Back 5

REST states a few key design principles:

* Application functionality is divided into resources
* Every resource is uniquely addressable using an URI
* All resources share a uniform interface for the transfer of state between client and resource.

Front 6

How does the router works?

Back 6

The conf/routes file is the configuration file used by the Router. This file list all the routes needed by the application. Each route consists of an HTTP method + URI pattern associated to a Java call.

Let’s see what a route definition looks like:

GET /clients/{id} Clients.show

Front 7

What HTTP methods are there?

Back 7

* GET
* POST
* PUT
* DELETE
* HEAD

Front 8

Give examples for dynamic URI

Back 8

/clients/{id}

or

/clients/{id}/accounts/{accountId}

Front 9

What is needed to map a controller to an URI?

Back 9

An URI is mapped to a method of a controller

A Controller class must be defined in the controllers package and must be a subclass of play.mvc.Controller.

The mapping is done in the router file with:
GET /admin admin.Dashboard.index

Front 10

What is the controller?

Back 10

a glue between the domain model objects (from the database) and the transport layer events (from the webbrowser)

Front 11

What is an URI?

Back 11

Uniform Resource Identifier (URI) is a string of characters used to identify or name a resource on the Internet. Such identification enables interaction with representations of the resource over a network (typically the World Wide Web) using specific protocols.

Front 12

How can data be retrieved from an HTTP request?

Back 12

* The URI path: in /clients/1541, 1541 is dynamic part of the URI Pattern.
* The Query String: /clients?id=1541.
* The request body: if the request was sent from an HTML form, the request body contains the form data encoded as x-www-urlform-encoded.

Front 13

What is the domain object model?

Back 13

. It’s the domain-specific representation of the information on which the application operates.

Martin fowler defines it as:

Responsible for representing concepts of the business, information about the business situation, and business rules. State that reflects the business situation is controlled and used here, even though the technical details of storing it are delegated to the infrastructure. This layer is the heart of business software.

Front 14

What is LightTPD?

Back 14

ighttpd (usually pronounced "Light-TPD", abbreviated "Lighty") is a web server designed to be secure, fast, standards-compliant, and flexible while being optimized for speed-critical environments.

Front 15

How do you create a new project?

Back 15

play new [project]

Front 16

What is the directory structure of the webapp?

Back 16

app/ contains the core of the application, split between models, controllers and views directories. It can contains other Java package as well. This is the directory where *.java source files live.

conf/ contains all the configuration files of the application, especially the main application.conf file, the routes definition files and the messages files used for internationalization.

lib/ contains all optional Java libraries packaged as standard .jar files.

public/ contains all the publicly available resources, which includes Javascript files, stylesheets and images directories.

test/ contains all the application tests. Tests are either written either as Java JUnit tests or as Selenium tests.

Front 17

How do you run a play application?

Back 17

play run [project]

Front 18

What is the default function of a controller?

Back 18

public static void index() {
render();
}

Front 19

What is the most common way to generate an HTTP response?

Back 19

Render a template from a controller: Using a template is the most common way (but not the only one) to generate the HTTP response.

Front 20

What are templates?

Back 20

Templates are simple text files that live in the /app/views directory. Because we didn’t specify a template, the default one for this action will be used: Application/index.html

To see how the template looks like, open the /yabe/app/views/Application/index.html file:

#{extends 'main.html' /}
#{set title:'Home' /}

#{welcome /}

The template content seems pretty light. In fact, all you see are play tags. Play tags are very close to JSP taglib. This is the #{welcome /} tag that generates the welcome message you’ve seen in the browser.

Front 21

How can I connect to a database?

Back 21

A database (either in memory or written to the filesystem) can be added by a line in the conf/application.conf file