Massimo Caliman
by Massimo Caliman
1 min read


  • Java


  • Java
  • JavaServer Faces
  • Programming Languages

When using tags like inputHidden or form, i.e. standard HTML components of the JSF, the id attributes of the corresponding HTML tag are automatically generated according to precise rules.



gives rise to this HTML code

<input type="hidden" name="form:field1"/>

Obviously we don’t have to value the id attribute, the Java Server Faces rendering takes care of automatically generating appropriate and unique ones.

However, when we want to reference a given component by its id, whether in CSS or Javascript, this behaviour prevents us from doing so (at the very least, it makes life difficult, think of referencing something like #form:field1 with JQuery, escape?).

In cases like this we can declare the id and at the form level specify the prependId="false" attribute. Applied to the code seen above we have



which will result in 

<input type="hidden" name="field1"/>

It would be tempting to use it all the time, even if it is not necessary for interactions with js or css. The attribute should be used with care, you may get a duplicate id error if you use it too often. In other words, if not strictly necessary, let JSF take care of these details and generate unique ids for our tags.