# Working With Event Handlers
Event handlers are the controller layer in ColdBox and is what you will be executing via the `URL`or a `FORM`post. All event handlers are **singletons**, which means they are cached for the duration of the application, so always remember to var scope your variables in your functions.
{% hint style="success" %}
**Tip:** For development we highly encourage you to turn handler caching off or you will have to reinit the application in every request, which is annoying. Open the `config/ColdBox.cfc` and look for the `coldbox.handlerCaching` setting.
{% endhint %}
Once you started the server in the previous section and opened the browser, the default event got executed which maps to an event handler CFC (controller) `handlers/main.cfc` and the method/action in that CFC called `index()`. Go open the `handlers/main.cfc` and let's explore the code.
## Handler Code
```javascript
// Default Action
function index( event, rc, prc ){
prc.welcomeMessage = "Welcome to ColdBox!";
event.setView( "main/index" );
}
```
Every action in ColdBox receives three arguments:
* `event` - An object that models and is used to work with the current request
* `rc` - A struct that contains both URL/FORM variables (unsafe data)
* `prc` - A secondary struct that is private only settable from within your application (safe data)
This line `event.setView( "main/index" )` told ColdBox to render a view back to the user found in `views/main/index.cfm` using a default layout, which by convention is called `Main.cfm` which can be found in the `layouts` folder.
## Executing Events
We have now seen how to add handlers via CommandBox using the `coldbox create handler` command and also execute them by convention by leveraging the following URL pattern:
```
http://localhost:{port}/folder/handler/action
http://localhost:{port}/handler/action
http://localhost:{port}/handler
```
Also remember, that if no `action` is defined in the incoming URL then the default action of `index` will be used.
{% hint style="info" %}
Remember that the URL mappings support in ColdBox is what allows you to execute events in such a way from the URL. These are controlled by your application router: `config/Router.cfc`
{% endhint %}
## Working With Incoming Data
Now, let's open the handler we created before called `handlers/hello.cfc` and add some public and private variables to it so our views can render the variables.
```javascript
function index( event, rc, prc ){
// param an incoming variable.
event.paramValue( "name", "nobody" );
// set a private variable
prc.when = dateFormat( now(), "full" );
// set the view to render
event.setView( "hello/index" );
}
```
Let's open the view now: `views/hello/index.cfm` and change it to this:
```markup
Hello #encodeForHTML( rc.name )#, today is #prc.when#
```
{% hint style="danger" %}
Please note that we used the ColdFusion function `encodeForHTML()` () on the public variable. Why? Because you can **never** trust the client and what they send, make sure you use the built-in ColdFusion encoding functions in order to avoid XSS hacks or worse on incoming public (`rc`) variables.
{% endhint %}
If you execute the event now: `http://localhost:{port}/hello/index` you will see a message of `Hello nobody`.
Now change the incoming URL to this: `http://localhost:{port}/hello/index?name=ColdBox` and you will see a message of `Hello ColdBox`.
{% hint style="success" %}
**Tip:** Please see the [layouts and views](https://coldbox.ortusbooks.com/v4.x-1/the-basics/layouts-and-views) section for in-depth information about them.
{% endhint %}
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