Facing new challenges everyday

In the last week I had several issues during the development of a jsf application that could be solved by creating few custom Facelets EL functions, let’s take a look on which scenarios Facelets EL functions helped me.

1. Simple loop over a range of numbers

JSF has a lot of components that can be used to iterate over a model and repeat its own child components several times, some of them are Tomahawk’s dataList and Richfaces repeat.

But in all of these components I couldn’t find a way to do a simple iteration on a range of numbers, like repeat all child components starting from 1 and stopping at n number of times.

Maybe you will say: “What about c:forEach? It can do this kind of iteration!”, oh yes, it can, and I tried to use it but it crashes when I pass EL expressions to both begin and end attributes, it only accepts hardcoded values.

In order to solve my issue, I created a custom Facelets EL function, this EL function takes a integer as argument that will be used to specify the size of a very simple List that will used on a Tomahawk’s dataList tag.

Look the code below:

ELFunctions.java:

To use the EL function on your page you must register as Facelets EL function in the file below:

target.taglib.xml:

And now you are ready to use it with any jsf repeater component:

wizardSteps.xml:

In the example above I realy need repeat the child components only n times and to get it a list with a limited size was created.

2. Converting a value passed to a f:param.

The are some circunstances where a h:outputFormat can help a lot on some ui data translation (e.g. returning a week day name from a number), but it need the number of week day to be passed as param, and for this I’m using a f:param.

But what if this param isn’t a integer? We need convert this data, right? I tried to figure out how can I do it by attaching a converter to a f:param, but I couldn’t find nothing about it anywhere.

How do I solved it? Simple, I just wrote another EL function that can takes any Object as an argument and then I returned a integer value of this object.

The code below shows how can I do it:

ELFunctions.java:

Now I must register the EL function in the same way as described previously:

target.taglib.xml:

Let’s take a look why I created this function:

outputWeekDays.xhtml:

In the example above I’m passing a week day number to week_days resource string used by outputFormat component.

This is the week_days resource string used in the code above:

The resource string above is expecting a parameter, the appropriate week day name will be picked based on day number passed by param tag attached to outputFormat tag.

As we can see, I’m iterating over a array of strings, each element is a string and when I passed this string to a outputFormat component I got a conversion error, with this EL function I could solve my problem very fast.

Here we have two examples of how we can use EL function to solve some annoying problems, there’s a lot of jsf issues that can be solved in this way too!