Use Custom Functions to Render Set with h:dataTable

I have a project that uses JSF and Hibernate. Today, I was trying to use h:dataTable to render a Set. What surprised me was that h:dataTable would only support UIData, which excluded Set. Heavily influenced by Hibernate, my project uses Set quite extensively. It would therefore be very annoying to change every Set into a UIData-supported collection, such as a List.

Solutions found on Google here and here suggest workarounds either using the map hack or custom components. Well, the map hack is a “hack,” so I’m not really a fan of that. Creating custom components is just trying to reinvent the wheel, so I’m also against it.

The solution that I have is simpler. I created a static function, that would convert a Set into an array, and registered it as an EL function. When passing the Set to dataTable, just wrap the Set with the function.

Specifically, I declare my own taglib, in /WEB-INF/functions.taglib.xml:

```
<?xml version="1.0" encoding="UTF-8"?>
```
```
<!DOCTYPE facelet-taglib PUBLIC
```

	"-//Sun Microsystems, Inc.//DTD Facelet Taglib 1.0//EN"

	"http://java.sun.com/dtd/facelet-taglib_1_0.dtd">

```
<facelet-taglib>
```
```
    <namespace>/functions</namespace>
```
```
	<function>
```

		<function-name>toArray</function-name>

```
		<function-class>
```

			com.ms.design.web.util.ExpressionLanguage

```
		</function-class>
```
```
		<function-signature>
```

			java.lang.Object[] toArray(java.util.Collection)

```
		</function-signature>
```
```
	</function>
```
```
</facelet-taglib>
```

```
<context-param>
```

	<param-name>facelets.LIBRARIES</param-name>

	<param-value>/WEB-INF/functions.taglib.xml</param-value>

```
</context-param>
```

The content of com.ms.design.web.util.ExpressionLanguage is:

```
package com.ms.design.web.util;
```
```
 
```
```
import java.util.Collection;
```
```
 
```
```
public class ExpressionLanguage {
```
```
 
```
```
	@SuppressWarnings("rawtypes")
```

	public static Object[] toArray(Collection collection) {

```
		return collection.toArray();
```
```
	}
```
```
 
```
```
}
```

That’s it. I can now use the function like:

```
<!DOCTYPE html>
```

<html xmlns="http://www.w3.org/1999/xhtml"

```
	xmlns:h="http://java.sun.com/jsf/html"
```
```
	xmlns:f="http://java.sun.com/jsf/core"
```
```
	xmlns:ms="/functions"
```

	xmlns:ui="http://java.sun.com/jsf/facelets">

```
 
```
```
…
```
```
 
```

		<h:dataTable value="#{ms:toArray(projectController.projects)}"

			var="project" frame="above" rules="all" styleClass="data"

			headerClass="header" rowClasses="odd,even"

```
			summary="A table of projects.">
```
```
…
```

So far, it works great. The only potential problem is the performance overhead caused by copying of the data. Fortunately, unlike c:forEach, h:dataTable only attempts to retrieve the value once, prior to rendering. If performance problem does occur, however, just switch to a List, or any other UIData-supported collections.

Update on February 23, 2011:
OpenFaces provides o:dataTable, which iterates any Collection. It would be a good solution, too.

BradChen.com

Use Custom Functions to Render Set with h:dataTable

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