Q1. How do you create a form in Spring MVC?
Use JSP with Spring form tags (e.g., form:form, form:input) or Thymeleaf. The form backing object is exposed as a model attribute. Example in JSP:
Q2. What is BindingResult?
BindingResult holds the result of data binding and validation. It must come immediately after the model attribute annotated with @Valid. It allows you to check for errors and access them in the view.
Q3. How do you display validation errors in the view?
Using form:errors tag in JSP or Thymeleaf's th:errors. The errors are automatically added to the model by BindingResult. You can iterate over them or show field-specific errors.
Q4. How do you perform custom validation?
Implement Validator interface or create custom annotation with ConstraintValidator. For cross-field validation, you can use class-level constraints. Example:
@Target({TYPE})
@Retention(RUNTIME)
@Constraint(validatedBy = PasswordMatchesValidator.class)
public @interface PasswordMatches { ... }
Q5. What is the role of @InitBinder?
@InitBinder methods in controllers allow you to configure data binding, such as setting allowed/disallowed fields, registering custom property editors, or adding validators. It runs before the handler method.