Action By Name

How many blogs have I read lately, where the authors first words are: “It’s been a while since my last post”. I can not do anything other than the same, because it has been a while.

To the point. I’m working on a Java project in school right now. Coming from a long time development in Rails, I got tired of all the typing and asked myself: Where did all the “It just works” go? And I came to the conclusion that there is none, or very little. So I took matters in to my own hands and created a somewhat Rails like functionality for controllers.

As all Rails developers know, or at least should know, the controller is determined by params[:controller] and the action by params[:action]. So what I did was something similar, only that you in Java can not pass params, as you can in Rails.

By name

Basically how it works is that when you create a controller you extend ApplicationController, that in turn extend ActionController. Example with one save method (or action).

public class SomeController extends ApplicationController
{
  public void save()
  {
    // Do the saving...
  }
}

Then say we want to call that method when a button is pressed. By extending ApplicationController it is as simple as this:

JButton save = new JButton("Save");
save.addActionListener(someController);
save.setName("save");

Almost like in Rails. You specify controller and action, and then Rails does the rest. Now when you click the save button, the method save in SomeController will be called automatically. Easy, right? Or, at least as easy as it can be in Java.

Method Missing

After a while I was assigned a task and doing it I discovered some limitations. The task was to create a menu, in which you could switch between all different languages. Adding a new language to the application is as easy as putting a YAML-file in a directory (À la Rails). So I created the menu dynamically from all yml-files. I also created a controller named LanguageController, that should receive actions when the language should change.

I discovered that to make this happen, I had to create one method in the controller for each locale (sv, en, fi, etc…). And that was clearly not an option. So in ActionController I added some new functionality. Most of you Ruby and Rails developers know it. I’m talking about method-missing.

How it works is simple. If there’s no method in the controller, with the same name as the component, the method methodMissing in ActionController is called. So in my case it was as simple as in LanguageController override methodMissing and implement the language switching.

Interesting

If you want to know more. Read the few lines of code and it’s many lines of comments. It’s at Github. There’s also a simple example included.