This article runs through the quick exercise of implementing the “Hello World” application from the Play! example.

Let’s start with the myapp project that we created previously.

Edit the app/views/App/Index.html template to add this form, under the included flash.html template:

<form action="/App/Hello" method="GET">
    <input type="text" name="myName" /><br/>
    <input type="submit" value="Say hello!" />
</form>

Refresh the page to see our work.

Let’s try submitting that form.

That makes sense. Add the action to app/controllers/app.go:

func (c App) Hello(myName string) revel.Result {
	return c.Render(myName)
}

Next, we have to create the view. Create a file app/views/App/Hello.html, with this content:

{{set . "title" "Home"}}
{{template "header.html" .}}

<h1>Hello {{.myName}}</h1>
<a href="/">Back to form</a>

{{template "footer.html" .}}

Refresh the page, and you should see a greeting:

Lastly, let’s add some validation. The name should be required, and at least three characters.

To do this, let’s use the validation module. Edit your action in app/controllers/app.go:

func (c App) Hello(myName string) revel.Result {
	c.Validation.Required(myName).Message("Your name is required!")
	c.Validation.MinSize(myName, 3).Message("Your name is not long enough!")

	if c.Validation.HasErrors() {
		c.Validation.Keep()
		c.FlashParams()
		return c.Redirect(App.Index)
	}

	return c.Render(myName)
}

Now it will send the user back to Index() if they have not entered a valid name. Their name and the validation error are kept in the Flash, which is a temporary cookie.

The provided flash.html template will show any errors or flash messages:

{{if .flash.success}}
<div class="alert alert-success">
	{{.flash.success}}
</div>
{{end}}

{{if or .errors .flash.error}}
<div class="alert alert-error">
	{{if .flash.error}}
		{{.flash.error}}
	{{end}}
	{{if .errors}}
	<ul style="margin-top:10px;">
		{{range .errors}}
			<li>{{.}}</li>
		{{end}}
	</ul>
	{{end}}
</div>
{{end}}

When we submit that form with a name that fails validation, we want the form to retain the bad name, so that the user can edit it before re-submitting. Amend the form you had added to your app/views/App/Index.html template:

<form action="/App/Hello" method="GET">
	
		<input type="text" name="" value=""/><br/>
	
	<input type="submit" value="Say hello!" />
</form>

Now when we submit a single letter as our name:

Success, we got an appropriate error and our input was saved for us to edit.