Wednesday, August 26, 2009

Testing GSP Custom Tags

In Grails: A Quick-Start Guide we used several custom tags. Unfortunately we didn't get a chance to write any tests for these tags. So let's do that now.

In GQuick we have a loginToggle tag which will display a "login" link if no user is logged in and a "logout" link if a user is logged in.

  def loginToggle = {

    out << "<div>"

    if (session.user){

      out << "<span>"

      out << "Welcome ${session.user}."

      out << "</span><span>"

      out << "<a href='${createLink(controller:'tekUser',  


      out << "Logout </a></span>"



      out << "<span>"

      out << "<a href='${createLink(controller:'tekUser',


      out << "Login </a></span>"


    out << "</div><br/>"


As you can see from the tag code, we are storing a reference to our user object in the session. If we find a user we display a welcome message and a Logout link. If there is no user we just display the Login link. Let see how we can write a unit test for this tag.

When we create a taglib with the grails create-tag-lib command, a corresponding test is created for us which extends the TagLibUnitTestCase class. This class makes testing taglibs a piece of cake. Take a look at the following test:

    void testLoginToggleWithUser() {

        mockSession.user = "user"

        def output = tagLib.loginToggle().toString()

        assert output.contains('Logout')

        assert output.contains('action=logout')


The first thing you'll notice is that we are setting the value of user on the mockSession object. This is one of the mock objects that are included in the TagLibUnitTestCase. Also included are mockRequest, mockResponse, mockParams, and mockFlash. Any calls to session in our tag code will be directed to this mockSession. So, when we look for the existence of a user to determine which text to display, we will find one.

In the next line we call the tag as a method of the implicit tagLib object. This object is loaded for us by the TagLibUnitTestCase. We don't need to declare or create it. It's just there and ready for us to use. Every tag in the tagLib can be called as a method. All of these tag methods return an instance of We call toString() on this to get a String representation of what the tag would have sent to the page.

Next we just makes some assertions on that output. We know that, if a user is in the session, we should have the word 'Logout' in the tag's output, so we can check for that with the contains() method. We'll talk about the second assertion in a minute. But first, if we were to run this test it would fail with an error because out tag calls the createLink tag that comes with Grails and none of the built-in Grails tags are available to unit tests.

Groovy makes this easy to handle. Let's just add the following line to our test class' setUp() method.

tagLib.metaClass.createLink = {map -> "action=${map.action}"}

Make sure to add this after the call to super.setUp() so that the tagLib object will be there. Now when a call to createLink is made within our tagLib it will call the method on the tagLib.metaClass which will return a string with the name of the action that the createLink would have linked to. This allows us to verify that we are passing the correct action, in this case 'logout'.

To be thorough, we'll also write a test to verify the behavior of our tag when there is no user logged in.

    void testLoginToggleNoUser() {

        def output = tagLib.loginToggle().toString()

        assert output.contains('Login')

        assert output.contains('action=login')


Now that we see how easy it is to write unit tests for Grails tagLibs we have no excuse for leaving those auto-generated test classes empty.

Saturday, August 15, 2009

Display An Image Property In a GSP

This is the first post for the GQuick blog. In this blog I plan to include helpful tips about Grails that we weren't able to get to in the book as well as address questions that come up from readers.

To kick this off we'll look at something that a couple readers of the beta ebook have asked about: Displaying the Sponsor logo in a GSP.

For those who haven't read the book, a bit of background. We have a Sponsor class which represents organizations that might sponsor a technical event. Here's an abbreviated listing of the Sponsor class:
class Sponsor {
byte[] logo

static constraints = {
logo(nullable:true, maxSize:1000000)

This will give us, in most databases, a BLOB type in which we can store an image of our sponsor's logo. Grails' scaffolded views provide the file upload mechanism for us but they don't provide a way to display the stored image in our pages. But don't worry, it's a piece of cake, this is Grails after all.

The first thing we'll do is add an action to our SponsorController called displayLogo.
class SponsorController {

def displayLogo = {
def sponsor = Sponsor.get(
response.contentType = "image/jpeg"
response.contentLength = sponsor?.logo.length

In this action we are retrieving a Sponsor with the id being passed in the params. Then we set a couple properties on the response object that is automatically injected into all Grails controllers. We set the contentType to "image" and the contentLength to the length of the logo property of the Sponsor instance. Finally we write the sponsor.logo to the outputStream of the response. Pretty simple so far.

The next step is to call this action in our GSP. To do this we'll use the createLink tag within an img tag, like so:

<img src="${createLink(action:'displayLogo', id:sponsorInstance?.id)}" />

Now if we drop this in our sponsor/show.gsp in place of the current ${sponsorInstance?.logo} (which spits out a bunch of binary goodness) we will get... an x or a ? depending on which browser we're using. Don't panic, this is just our SecurityFilter trying to help us out. ( For those who haven't read GQuick, we have a SecurityFilter that checks for a logged in user for all actions but those listed in the allowedActions list).

So, let's add displayLogo to the allowedActions list, like this:

def allowedActions = ['show', 'index', 'list', 'login',
                      'validate', 'search', 'displayLogo']
Note: this step is only necessary if you've been following along with the TekDays application in Grails: A Quick-Start Guide. If you are just using this technique in your own application then you're already done.

Now when we view one of our sponsors it will look more like this: