Let's update the code of AddController.java by following these steps:

1. Add a method to bind the validator to WebDataBinder, and annotate it by @InitBinder, as follows:

@InitBinder 
private void initBinder(WebDataBinder webDataBinder) 
{ 
  webDataBinder.setValidator(validator); 
} 

The @InitBinder annotation helps in identifying the methods that perform the WebDataBinder initialization.

2. To enable the annotations to be considered by the framework, the book-servelt.xml file has to be updated:
   1. Add the mvc namespace as shown in the following configuration:

    <beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:context="http://www.springframework.org/schema
    /context" 
    xmlns:mvc="http://www.springframework.org/schema/mvc" 
    xsi:schemaLocation="http://www.springframework.org/
    schema/beans 
    http://www.springframework.org/schema/beans/
    spring-beans.xsd  
    http://www.springframework.org/schema/context  
    http://www.springframework.org/schema/context/
    spring-context.xsd 
    http://www.springframework.org/schema/mvc 
    http://www.springframework.org/schema/mvc/spring-mvc.xsd"> 

You can only copy the highlighted statements in your existing code.

2. Add the configuration as follows:

 <mvc:annotation-driven/> 

3. Update the addBook() method to add the @Valid annotation to perform book validation, and remove the validator.validate() invocation, as it will be executed implicitly. The updated code is as follows:

@RequestMapping("/addBook.htm") 
public ModelAndView addBook(@Valid @ModelAttribute("book")  
   Book book,BindingResultbindingResult) 
throws Exception { 
  //validator.validate(book, bindingResult); 
  if(bindingResult.hasErrors()) 
  { 
    return new ModelAndView("bookForm"); 
  } 
  ModelAndView modelAndView = new ModelAndView(); 
  modelAndView.setViewName("display"); 
  //later on the list will be fetched from the table 
  // rest of the code is same as the earlier implemenation 
} 

4. Run the application to get the similar result when you submit a blank form. The messages displayed in the view are hardcoded in the rejectValue() method. The framework provides a support for externalizing the messages in the properties file. Let's update the Validator for externalizing messages.