JavaServer Faces

Create FacesMessage within a get-method

2008/02/09 in Blog - 1 Comment

Lately I had problems with displaying a FacesMessage. I suspected that it was due to creating it inside a property get-method. As a proof I created a simple demo application.

public class CreateFacesMessageController {
	public String newFacesMessage() {
		new FacesMessageSupport().error("TEST");
		return "success"
	}

	public String getFacesMessage() {
		System.out.println("get-method");
		return newFacesMessage();
	}
}

The class above contains an action method that creates FacesMessage instance and adds it to the FacesContext through some helper class. A get-method (for pseudo property facesMessage) calls this action method.

A JSP view is using these methods to show the effect described.

The JSP contains a button that triggers the action method, every time it is clicked a faces message is shown.
It also shows the property facesMessage which is bound to the method getFacesMessage.

So one would think that every time the view is show, it also produces a faces message on top of the form – it doesn’t. Here is why:

As a result the messages have alread been rendered when the new faces message is created. You only have 2 choices to remedy. Either you move the messages tag to the very bottom of the form or you make sure that any method that is possibly creating a faces message is invoked in an earlier phase than the RENDER_RESPONSE phase!

Creating JSF SelectItem

2007/08/08 in Blog - 7 Comments

Creating SelectItem lists for dropdown and list controls is a pretty boring task. Everytime you do it, it’s like why isn’t this already part of JSF – it’s the same stupid task again and again.

So I was like – I should help myself and create something reusable, a component! I have been using JSF now for a while but only slowly I’m starting to write my own JSF components (creating a JSF component is a pretty heavy task, this should get easier in future releases of the JSF specification!).

This time it came to my mind that JSP allows to create EL functions that only require a class with a static method, a tag library descriptor and can be packaged easily into a JAR. So I’d wish a function that can be used in a JSF JSP to convert any collection like type such that JSF can display it through one of its selectOne, selectMany, etc. components.

<%@ taglib uri="http://at.martinahrer.blueprint.faces.el.si" prefix="si"%>

So the selectItem function would just do it’s job and no longer my presentation logic would get polluted with all this collection iterations and SelectItem instantiations.
Sounds interesting, but what is required to implement this function?First we need a tag library descriptor that is dropped somewhere into the WEB-INF folder. And we need the Java code that is actually doing all the heavy job.

        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd">
	1.0.0
	si
	http://at.martinahrer.blueprint.faces.el.si
	
		selectItems
		at.martinahrer.blueprint.faces.el.SelectItems
		
			java.util.Map selectItems(java.lang.Object,java.lang.String,java.lang.String)
		
	

public class SelectItems {
	public static Map selectItems(Object value, String labelExpression, String variable) {
		assert (variable != null);

		Collection