Understanding the "Welcome to Play 2.0" page creation

Question

I have just started to try to work with the play framework and tried to understand this default application you get when creating a new project.

So as far as I understand, when loading the localhost page, a http get request comes in and is directed to the Application.index() method because of the specification in the routes file? In the index() method a lot of HTML code is generated and returned in a Result object and passed to the index.scala.html file which hands it over to the main.scala.html where it is surrounded with more html.

Now, a few things are unclear to me:

• in Application.java there is this line return ok(index.render("Hello World!")); index belongs to views.html.*; but where is this package? I can't find it in the API :(

• why can't I rename the index.scala.html file? Is the name a convention?

• in the index.scala.html file itself: what does @play20.welcome(message, style = "Java") do? is this getting the "Welcome to Play 2.0" site? and again - I can't find the documentation/API entry for the play20 thing :(

I hope, somebody can help me to get an overview, as I am really confused at the moment..^^ I have done a lot of java, but no web programming at all, therefore this mix of all the different technologies and languages is quite strange at the moment!

Answer 1

In the TodoList example, the site root GET / is mapped to the method Application.index(), so this method creates the html you are seeing.

Everything the controller does happens in this line: return ok(index.render("Hello World!"));. Basically it calls some templates which generate html and returns the output.

• return ok( ... ) is used to indicate a successful request, return code 200.
• index.render( ... ) returns the rendered html output of a template named index. The package used here is views.html.* but it actually refers to views/index.scala.html. So the index part is no convention, you can rename that part as you like. The template needs to get compiled before it is usable like a Java class, that's why the package names are different. The framework takes care of this.
• "Hello World!" is the argument, as specified as message parameter in the very first line of index.scala.html
• @play20.welcome( ... ) just calls another template, a welcome page which is included in the framework. It's not a subject to change - it's just static page, after removing that line from the view you can put any HTML you want.