Tobago has JSR 303 Validation support. With it, you can describe the validation in an annotation in the controller.

In this example, the input cannot be empty - in other words, it's required. The value in the controller is annotated with `@NotNull`.

    <tc:in label="Input" value="\#{validationJsr303Controller.required}"/>

    @NotNull
    private String required;

The length of the given string must be between 2 and 4 characters.

    <tc:in label="Input" value="\#{validationJsr303Controller.length}"/>

    @Size(min = 2, max = 4, message = "Length must be between 2 and 4")
    private String length;