JSF Tip #8 - Writing your own Validator

Writing your own validator is a straightforward process. It involves implementing the Validator API and making sure you register it properly.

Say you want to write a validator that will not allow you to use the string "Hello World" as a value.

    package nohelloworld;

    public class NoHelloWorldValidator implements Validator {

        public void validate(FacesContext context, UIComponent component, Object value) 
            throws ValidatorException
            if (value != null && "Hello World".equals(value.toString()) {
                throw new ValidatorException(new FacesMessage("Hello World is invalid"));
            }
        }
    }
        

To make sure you can use your custom Validator you will need configure it so the JSF runtime knows about it. Adding it to your faces-config.xml will do the trick.

            
    <validator>
        <validator-id>NoHelloWorldValidator</validator-id>	
        <validator-class>nohelloworld.NoHelloWorldValidator</validator-class>
    </validator>
        

And hooking this validator up to a inputText would be done as follows.

    <h:inputText value="#{echo.message}">
        <f:validator validatorId="NoHelloWorldValidator"/>
    </h:inputText>
        

Posted September 9, 2012

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