Validation

Notice that each <h:inputField> tag has a nested <f:validateLength> tag. As its name implies, this tag validates that the entered value for the text field is between a minimum and maximum length. Minimum and maximum values are defined by the tag's minimum and maximum attributes. <f:validateLength> is one of the standard validators included with JSF. Just like with the required attribute of <h:inputText>, JSF will automatically display a default error message when a user attempts to submit a form with a value that does not validate:

Again, the default message and style can be overridden; we will cover how to do this later in the chapter.

In addition to <f:validateLength>, JSF includes other standard validators, which are listed in the following table:

Notice that in the description for <f:validateBean>, we briefly mentioned bean validation. The bean validation JSR aims to standardize JavaBean validation. JavaBeans are used across several other APIs that, up until recently, had to implement their own validation logic. JSF 2.0 adopted the bean validation standard to help validate named bean properties.

If we want to take advantage of bean validation, all we need to do is annotate the desired field with the appropriate bean validation annotation, without having to explicitly use a JSF validator.

For a complete list of bean validation annotations, refer to the javax.validation.constraints package in the Java EE 8 API at https://javaee.github.io/javaee-spec/javadocs/.