developing web applications using Java and the Play framework

WHAT IS PLAY?• A clean alternative to the bloated Java Enterprise Edition

• Pure Java framework – allows you to keep your preferred development tools and libraries

• Focuses on developer productivity and targets RESTful (Representational State Transfer) architectures

• Consist of clients and servers

• Clients initiate requests to servers

• Servers process requests and return appropriate responses

• Requests and responses are built around the transfer of representations of resources

THE FOUNDATION OF PLAY• MVC architecture

• You’ve got a database on one side and a web browser on the other.

• Classes are models, the application is the controller, generated HTML is the view

• HTTP-to-code mapping

• Example: binding URI patterns to Java procedure calls

• Efficient template engine

• The expression language used is Groovy

• Templating system mainly used to render HTML responses

WHY IS PLAY AWESOME?• Fix the bug and hit reload

• The framework compiles your Java sources directly and hot-reloads them into the JVM without the need to restart the server

• You can then edit, reload and see your modifications immediately, just as in a Rails environment

• Whenever an error occurs, the framework identifies and shows you the problem

• Stack traces are stripped down and optimized to make it easier to solve problems

• Java Persistence API (JPA) and The Java Persistence Query Language (JPQL)

• A persistence entity is a lightweight Java class saved to a table in a relational database.

JPA, JPQL// Java Persistence API example@Entity public class Book {

@Id private Integer id; private String title; private String isbn;

@ManyToOne private Publisher publisher;

@ManyToMany private List<Author> authors;

}

JPA, JPQL// Java Persistence Query Language examplepublic void messages(int page, User connectedUser ) {

List<Message> messages = Message.find(“user = ? and read = false order by date desc", connectedUser).from(page * 10).fetch(10);

render(connectedUser, messages); }

WHY IS PLAY AWESOME?• Test-driven development

• Run them directly in a browser using Selenium

• Selenium is a Firefox add-on that records clicks, typing, and other actions

• Database support through JDBC

• Object-relational mapping using Hibernate (with the JPA API)

• Integrated cache support

• Straightforward web services consumption either in JSON or XML

• OpenID support for distributed authentication

• Ready to be deployed anywhere (application server, Google App Engine, Cloud, etc…)

• Image manipulation API.

THINGS YOU CAN DO WITH PLAY

THINGS YOU CAN DO WITH PLAY• Bind an HTTP parameter to a Java method parameter

// a simple request/articles/archive?date=08/01/08&page=2

// the Java methodpublic static void archive(Date date, Integer page) {

List<Article> articles = Articles.fromArchive(date, page); render(articles);

}

THINGS YOU CAN DO WITH PLAY• Smart binding with any class

// a simple modelpublic class Person {

public String name; public Integer age;

}// a simple controllerpublic static void add(Person p) { p.save(); }

// a simple HTML form<form action="add" method="POST">

Name: <input type="text" name="p.name" /> Age: <input type="text" name="p.age" />

</form>

THINGS YOU CAN DO WITH PLAY• Redirect to an action by calling the corresponding Java method

// a simple model with a procedurepublic static void show(Long id) {

Article article = Article.findById(id); render(article);

}

// use the equivalent syntax:<a href="@{Article.show(article.id)}">

${article.title}</a>

THINGS YOU CAN DO WITH PLAY• Redirect to an action by calling the corresponding Java method (another example)

// a simple model with a procedurepublic static void edit(Long id, String title) {

Article article = Article.findById(id); article.title = title; article.save();

show(id); }

// generated HTML:<a href="/articles/15">

My new article</a>

THINGS YOU CAN DO WITH PLAY• Straightforward file upload management

// the Java codepublic static void uploadPhoto(String title, File photo) {

... }

// a simple HTML form<form action="@{Article.uploadPhoto()}" method="POST"

enctype="multipart/form-data">

<input type="text" name="title" /> <input type="file" id="photo" name="photo" /> <input type="submit" value="Send it..." />

</form>

DEMO

Let’s create our own web application:

a personal agenda

Questions?