7.6. Conversion and Validation

You can specify a JSF converter for complex model properties, in either of the following ways: 
<pages> 
  <page view-id="/calculator.jsp" action="#{calculator.calculate}"> 
    <param name="x" value="#{calculator.lhs}"/> 
    <param name="y" value="#{calculator.rhs}"/> 
    <param name="op" converterId="com.my.calculator.OperatorConverter" 
           value="#{calculator.op}"/> 
  </page> 
</pages>
<pages> 
  <page view-id="/calculator.jsp" action="#{calculator.calculate}"> 
    <param name="x" value="#{calculator.lhs}"/> 
    <param name="y" value="#{calculator.rhs}"/> 
    <param name="op" converter="#{operatorConverter}" 
           value="#{calculator.op}"/> 
  </page> 
</pages>
JSF validators, and required="true" may also be used, in either of the following ways: 
<pages> 
  <page view-id="/blog.xhtml"> 
    <param name="date" value="#{blog.date}" 
           validatorId="com.my.blog.PastDate" required="true"/> 
  </page> 
</pages>
<pages> 
  <page view-id="/blog.xhtml"> 
    <param name="date" value="#{blog.date}" 
           validator="#{pastDateValidator}" required="true"/> 
  </page> 
</pages>
Model-based Hibernate validator annotations are automatically recognized and validated. Seam also provides a default date converter to convert a string parameter value to a date and back.
When type conversion or validation fails, a global FacesMessage is added to the FacesContext.