Validate f:viewParam value to be one of a select set of allowable values

I am learning JSF 2.2 and I am having a little trouble finding a good answer that i can understand as to how to have more for validation on a GET parameter.

I have a source.xhtml file that has a link it like this:

<h:link value="ALTER" outcome="/main/showSqlTemplates.xhtml">
    <f:param name="type" value="ALTER" />
</h:link>

and in my destination.xhtml i have code that looks like this:

<f:metadata>
<f:viewParam id="type" name="type" value="#{showSqlTemplateManagedBean.type}" required="true" requiredMessage="Invalid page access. Please use a link from the menu."/>                    
</f:metadata>
<h:message for="type" class="bold"></h:message>
<br/>TYPE is : #{showSqlTemplateManagedBean.type}

and my bean class looks like this:

@ManagedBean
@RequestScoped
public class ShowSqlTemplateManagedBean {

    String type = "";

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public ShowSqlTemplateManagedBean() {

    }
}

as you can see i have used the "required" attribute to make sure the type parameter is at least there and everything is working fine as far as that goes. But i would like to do more validation.

Specifically I want to make sure the value of the String type will only be ALTER,INSERT,UPDATE OR DELETE.

Is this where a custom validator comes in? A custom validator seems to be over kill for such a simple validation check. I am sure I am missing something. Perhaps put something in the PostConstruct init() method?

Solution

Just make it an enum.

@ManagedBean
@RequestScoped
public class ShowSqlTemplateManagedBean {

    public enum Type {
        ALTER, INSERT, UPDATE, DELETE;
    }   

    private Type type;

    public Type getType() {
        return type;
    }

    public void setType(Type type) {
        this.type = type;
    }

}

JSF has a builtin converter for enumns which will kick in fully transparently. Any invalid value will cause a conversion error which you can customize via converterMessage attribute of the <f:viewParam>.

Enums have more benefits elsewhere in the code, too.

Unrelated to the concrete problem, explicitly initializing properties with an empty string (or even null) is poor practice. Don't do that anymore. Moreover, initializing managed bean properties with a non-empty-string or non-null should happen in a @PostConstruct annotated method.