jsf 2 - When to name a converter in JSF -

i've been working converters in primefaces selectonemenu objects. work fine if tell class converter referring to:

@facesconverter(forclass = descriptorvo.class) public class descriptorvoconverter implements converter { ... } 

this way, don't have explicitly tell jsf component converter should used when populated objects of class descriptorvo.

however, made page used p:selectmanycheckbox , couldn't life of me know why wasn't calling converter. gave name, so:

@facesconverter(forclass = rolevo.class, value = "rolevoconverter") public class rolevoconverter implements converter { ... } 

and passed 1 of component's properties

<p:selectmanycheckbox id="cbx_roles" required="true" converter="rolevoconverter"     requiredmessage="at least 1 role must selected."     value="#{userview.selectedroles}" layout="responsive">     <f:selectitems value="#{userview.roles}" var="role"         itemlabel="#{role.title}" itemvalue="#{role}" /> </p:selectmanycheckbox> 

and voi la, started calling converter correctly. raised question me regarding when should name converters (through value attribute) , when telling them class converter should used (with forclass attribute) enough. never had namy converters when working primefaces, particular selectmanycheckbox component. different components have different necessities regarding converters or did concept of converters wrong?

that can happen when value of uiselectmany component references generic java.util.collection type list<role> instead of array role[]. specified in javadoc of uiselectmany (emphasis mine):

obtain converter using following algorithm:

• if component has attached converter, use it.

• if not, valueexpression value (if any). valueexpression must point is:

  • an array of primitives (such int[]). registered by-class converter primitive type.
  • an array of objects (such integer[] or string[]). registered by-class converter underlying element type.
  • a java.util.collection. not convert values.

• if reason converter cannot found, assume type string array.

the reason is, generic type <role> lost during runtime , not directly determinable. works when you're using myfaces instead of mojarra in case of java.util.collection inspect actual type manually iterating on <f:selectitem(s)> , determine converter based on first non-null value.

i created spec issue 1422 on in jsf spec , improve mojarra too.

see also:

• uiselectmany on list<t> causes java.lang.classcastexception: java.lang.string cannot cast t
• why jsf put string values in map<..., integer>? , how work around it?
• use enum in h:selectmanycheckbox