Session 5 | Syntax Lab

This session (PDF)MCSL-222 Section 2 (ZIP)MCSL-222 (ZIP)Semester 2 (ZIP)

Validation happens twice: in the browser for fast feedback and on the server because the browser cannot be trusted. Bootstrap then gives the forms a consistent look without hand-written CSS for every element.

All four questions change the Session 4 admission form inside the student-admission project. The listings below are the end-of-session files; each question’s explanation points at the lines that answer it.

Objectives

Do not copy. Read for understanding and the viva

Complete questions 21 to 24 of the manual: form validation, bootstrap and css
Prepare the deliverable before the lab and finish it during the session
Be ready to explain every step in the viva

Questions Covered

Do not copy. Read for understanding and the viva

Question	Requirement	Status
Q21	Apply the client validation in the form created in the above exercise 4 of session 4,…	Complete
Q22	Write a programme to bind form objects with entity bean in Spring MVC	Complete
Q23	Configure Bootstrap in Spring MVC and use default styling classes in the form and view…	Complete
Q24	Apply custom Styling to your pages in Spring MVC	Complete

Preparation

Do not copy. Read for understanding and the viva

Server-side validation uses Bean Validation annotations (@NotBlank, @Size, @Past, @Email) on the form object and @Valid plus BindingResult in the controller.
Client-side validation is HTML5 attributes (required, pattern, min) or a few lines of JavaScript.
Include Bootstrap from a CDN link in the page head or add the WebJar dependency.

Question 21

Problem Statement

Write in lab record

Apply the client validation in the form created in the above exercise 4 of session 4, along with server-side validation.

Solution

Write in lab record

Steps

Add the hibernate-validator dependency from the fragment to pom.xml; Maven → Update Project.
Replace AdmissionForm.java with the annotated version. Every rule is an annotation on the field.
Replace admission-form.jsp. Client rules are HTML attributes on the inputs (required, minlength, pattern, max); server messages appear through form:errors.
Client test: rebuild, open /admission, leave the name empty and press Submit. The browser refuses to send the form and points at the field.
Server test: in the browser’s developer tools add novalidate to the form element (or run document.querySelector('form').noValidate = true in the console), submit the empty form. The page comes back with red messages under each field.

Program

Lab record: every tab is one file of the answer. Write all of them.

pom.xml (Q21 addition)xml

<!-- Q21: add inside <dependencies> of pom.xml. Hibernate Validator is the Bean
     Validation 3.0 provider; Spring MVC picks it up automatically for @Valid.
     Tomcat 10.1 supplies the Jakarta EL implementation it needs; add
     org.glassfish.expressly:expressly:5.0.0 only if you validate outside Tomcat. -->
<dependency>
  <groupId>org.hibernate.validator</groupId>
  <artifactId>hibernate-validator</artifactId>
  <version>8.0.1.Final</version>
</dependency>

web/AdmissionForm.javajava

package com.ignou.lab.admission.web;

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;
import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotEmpty;
import jakarta.validation.constraints.NotNull;
import jakarta.validation.constraints.Past;
import jakarta.validation.constraints.Pattern;
import jakarta.validation.constraints.Size;
import org.springframework.format.annotation.DateTimeFormat;
import com.ignou.lab.admission.entity.Student;

/** Form-backing object with server-side (Bean Validation) rules. */
public class AdmissionForm {

    @NotBlank
    @Size(min = 3, max = 80)
    private String name;

    @NotBlank
    @Email
    private String email;

    @NotBlank
    @Pattern(regexp = "[6-9][0-9]{9}", message = "must be a 10-digit Indian mobile number")
    private String mobile;

    @NotNull
    @Past
    @DateTimeFormat(iso = DateTimeFormat.ISO.DATE)
    private LocalDate dob;

    @NotBlank
    @Size(max = 255)
    private String address;

    @NotBlank
    private String programme;

    @NotNull(message = "choose Yes or No")
    private Boolean hostelRequired;

    @NotEmpty(message = "pick at least one course")
    private List<String> courses = new ArrayList<>();

    /** Q22: bind the form object to the entity bean. */
    public Student toStudent() {
        Student s = new Student();
        s.setName(name);
        s.setEmail(email);
        s.setMobile(mobile);
        s.setDob(dob);
        s.setAddress(address);
        s.setProgramme(programme);
        s.setHostelRequired(hostelRequired);
        s.setCourses(String.join(",", courses)); // entity column is one comma-separated string
        return s;                                // enrolmentNo stays null until approval (Session 6)
    }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public String getMobile() { return mobile; }
    public void setMobile(String mobile) { this.mobile = mobile; }
    public LocalDate getDob() { return dob; }
    public void setDob(LocalDate dob) { this.dob = dob; }
    public String getAddress() { return address; }
    public void setAddress(String address) { this.address = address; }
    public String getProgramme() { return programme; }
    public void setProgramme(String programme) { this.programme = programme; }
    public Boolean getHostelRequired() { return hostelRequired; }
    public void setHostelRequired(Boolean hostelRequired) { this.hostelRequired = hostelRequired; }
    public List<String> getCourses() { return courses; }
    public void setCourses(List<String> courses) { this.courses = courses; }
}

WEB-INF/views/admission-form.jsphtml

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%@ taglib prefix="c" uri="jakarta.tags.core" %>
<!DOCTYPE html>
<html lang="en">
<head>
  <%@ include file="head.jspf" %>
  <title>Student Admission Form</title>
</head>
<body>
<nav class="navbar navbar-dark"><div class="container"><span class="navbar-brand">IGNOU Student Admission</span></div></nav>
<div class="container">
  <div class="card card-form">
    <div class="card-body">
      <h1 class="h3 card-title">Student Admission Form</h1>

      <form:form modelAttribute="admission" method="post" cssClass="row g-3">
        <div class="col-12">
          <form:label path="name" cssClass="form-label required">Full name</form:label>
          <form:input path="name" cssClass="form-control" cssErrorClass="form-control is-invalid"
                      required="required" minlength="3" maxlength="80"/>
          <form:errors path="name" cssClass="invalid-feedback"/>
        </div>

        <div class="col-md-6">
          <form:label path="email" cssClass="form-label required">Email</form:label>
          <form:input path="email" type="email" cssClass="form-control" cssErrorClass="form-control is-invalid"
                      required="required"/>
          <form:errors path="email" cssClass="invalid-feedback"/>
        </div>

        <div class="col-md-6">
          <form:label path="mobile" cssClass="form-label required">Mobile</form:label>
          <form:input path="mobile" cssClass="form-control" cssErrorClass="form-control is-invalid"
                      required="required" pattern="[6-9][0-9]{9}" title="10 digits, starting 6 to 9"/>
          <form:errors path="mobile" cssClass="invalid-feedback"/>
        </div>

        <div class="col-md-6">
          <form:label path="dob" cssClass="form-label required">Date of birth</form:label>
          <form:input path="dob" type="date" cssClass="form-control" cssErrorClass="form-control is-invalid"
                      required="required" max="${today}"/>
          <form:errors path="dob" cssClass="invalid-feedback"/>
        </div>

        <div class="col-md-6">
          <form:label path="programme" cssClass="form-label required">Programme</form:label>
          <form:select path="programme" cssClass="form-select" cssErrorClass="form-select is-invalid" required="required">
            <form:option value="" label="-- choose --"/>
            <form:options items="${programmes}"/>
          </form:select>
          <form:errors path="programme" cssClass="invalid-feedback"/>
        </div>

        <div class="col-12">
          <form:label path="address" cssClass="form-label required">Address</form:label>
          <form:textarea path="address" rows="3" cssClass="form-control" cssErrorClass="form-control is-invalid"
                         required="required" maxlength="255"/>
          <form:errors path="address" cssClass="invalid-feedback"/>
        </div>

        <div class="col-md-6">
          <label class="form-label required">Hostel required?</label>
          <div class="form-check form-check-inline">
            <form:radiobutton path="hostelRequired" value="true" cssClass="form-check-input" label=" Yes" required="required"/>
          </div>
          <div class="form-check form-check-inline">
            <form:radiobutton path="hostelRequired" value="false" cssClass="form-check-input" label=" No"/>
          </div>
          <form:errors path="hostelRequired" cssClass="text-danger small d-block"/>
        </div>

        <div class="col-md-6">
          <label class="form-label required">Courses this semester</label>
          <c:forEach items="${courseList}" var="course">
            <div class="form-check">
              <form:checkbox path="courses" value="${course}" cssClass="form-check-input" label=" ${course}"/>
            </div>
          </c:forEach>
          <form:errors path="courses" cssClass="text-danger small d-block"/>
        </div>

        <div class="col-12 text-end">
          <a class="btn btn-outline-secondary" href="${pageContext.request.contextPath}/">Cancel</a>
          <button type="submit" class="btn btn-primary">Submit application</button>
        </div>
      </form:form>
    </div>
  </div>
</div>
</body>
</html>

Output

Expected, checked by reading, not executed. Client side: Chrome’s bubble “Please fill in this field” on the name box, and “Please match the requested format” with the title text on a mobile number like 12345. Server side (with novalidate), the form returns with these messages under the fields:

Full name        must not be blank
Email            must not be blank
Mobile           must not be blank
Date of birth    must not be null
Programme        must not be blank
Address          must not be blank
Hostel required? choose Yes or No
Courses          pick at least one course

A name of two letters with the browser check bypassed returns size must be between 3 and 80; a date of birth in the future returns must be a past date.

Explanation

Client validation is the HTML5 attributes: required on every field, minlength="3" maxlength="80" on the name, type="email", pattern="[6-9][0-9]{9}" on the mobile, type="date" max="${today}" so the picker cannot choose a future date, required on the select and on the first radio (it applies to the whole radio group). Checkboxes have no “at least one” attribute; only the server enforces that rule.
Server validation is Bean Validation: @NotBlank, @Size, @Email, @Pattern, @Past, @NotNull, @NotEmpty on AdmissionForm. Hibernate Validator is the provider; Spring MVC finds it on the classpath and runs it whenever a handler parameter carries @Valid (see the controller in Q22).
The rules match on both sides (same regex, same length limits) so a user with JavaScript on and a user posting with curl get the same answer.
cssErrorClass swaps the input’s class to form-control is-invalid when that field has an error; form:errors prints the message in a span with class invalid-feedback, which Bootstrap shows only next to an invalid control.

Question 22

Problem Statement

Write in lab record

Write a programme to bind form objects with entity bean in Spring MVC.

Solution

Write in lab record

Steps

Replace AdmissionController.java: the POST handler takes @Valid AdmissionForm and a BindingResult, and on success converts the form to a Student entity and saves it.
Add save() to StudentRepository.java.
Replace admission-result.jsp; it now shows the saved entity, including the generated database id.
Rebuild, submit a valid application, then check MySQL: SELECT id, name, programme, courses FROM ignou.student;.

Program

Lab record: every tab is one file of the answer. Write all of them.

web/AdmissionController.javajava

package com.ignou.lab.admission.web;

import java.time.LocalDate;
import java.util.List;
import jakarta.validation.Valid;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;
import com.ignou.lab.admission.entity.Student;
import com.ignou.lab.admission.repo.StudentRepository;

@Controller
public class AdmissionController {

    private static final List<String> PROGRAMMES = List.of("MCA", "BCA", "PGDCA");
    private static final List<String> COURSES = List.of(
            "MCS-218 Data Communication and Computer Networks",
            "MCS-219 Object Oriented Analysis and Design",
            "MCS-220 Web Technologies",
            "MCS-221 Data Warehousing and Data Mining");

    private final StudentRepository repo;

    public AdmissionController(StudentRepository repo) {
        this.repo = repo;
    }

    @ModelAttribute("programmes")
    public List<String> programmes() {
        return PROGRAMMES;
    }

    @ModelAttribute("courseList")
    public List<String> courseList() {
        return COURSES;
    }

    /** used by the date picker's max attribute (client-side @Past) */
    @ModelAttribute("today")
    public LocalDate today() {
        return LocalDate.now();
    }

    @GetMapping("/admission")
    public String showForm(Model model) {
        model.addAttribute("admission", new AdmissionForm());
        return "admission-form";
    }

    @PostMapping("/admission")
    public String submit(@Valid @ModelAttribute("admission") AdmissionForm form,
                         BindingResult result, Model model) {
        if (result.hasErrors()) {
            return "admission-form"; // re-render with form:errors filled in; user input is kept
        }
        Student saved = repo.save(form.toStudent()); // Q22: form object -> entity bean -> database
        model.addAttribute("student", saved);
        return "admission-result";
    }
}

repo/StudentRepository.javajava

package com.ignou.lab.admission.repo;

import java.util.List;
import jakarta.persistence.EntityManager;
import jakarta.persistence.PersistenceContext;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
import com.ignou.lab.admission.entity.Student;

@Repository
@Transactional
public class StudentRepository {

    @PersistenceContext
    private EntityManager em;

    @Transactional(readOnly = true)
    public List<Student> findAll() {
        return em.createQuery("from Student s order by s.id", Student.class).getResultList();
    }

    /** INSERT on commit; the generated id is set on the same object. */
    public Student save(Student student) {
        em.persist(student);
        return student;
    }
}

WEB-INF/views/admission-result.jsphtml

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib prefix="c" uri="jakarta.tags.core" %>
<!DOCTYPE html>
<html lang="en">
<head>
  <%@ include file="head.jspf" %>
  <title>Application saved</title>
</head>
<body>
<nav class="navbar navbar-dark"><div class="container"><span class="navbar-brand">IGNOU Student Admission</span></div></nav>
<div class="container">
  <div class="card card-form">
    <div class="card-body">
      <div class="alert alert-success">Application saved. Database id: <b>${student.id}</b></div>
      <table class="table table-striped">
        <tbody>
          <tr><th scope="row">Name</th><td><c:out value="${student.name}"/></td></tr>
          <tr><th scope="row">Email</th><td><c:out value="${student.email}"/></td></tr>
          <tr><th scope="row">Mobile</th><td><c:out value="${student.mobile}"/></td></tr>
          <tr><th scope="row">Date of birth</th><td>${student.dob}</td></tr>
          <tr><th scope="row">Address</th><td><c:out value="${student.address}"/></td></tr>
          <tr><th scope="row">Programme</th><td><c:out value="${student.programme}"/></td></tr>
          <tr><th scope="row">Hostel required</th><td>${student.hostelRequired ? 'Yes' : 'No'}</td></tr>
          <tr><th scope="row">Courses</th><td><c:out value="${student.courses}"/></td></tr>
          <tr><th scope="row">Enrolment no</th><td>${empty student.enrolmentNo ? 'pending approval' : student.enrolmentNo}</td></tr>
        </tbody>
      </table>
      <a class="btn btn-primary" href="${pageContext.request.contextPath}/admission">Another application</a>
      <a class="btn btn-outline-secondary" href="${pageContext.request.contextPath}/students">All students</a>
    </div>
  </div>
</div>
</body>
</html>

Output

Expected, checked by reading, not executed. Tomcat’s console shows the INSERT Hibernate issued:

Hibernate:
    insert
    into
        student
        (address, courses, dob, email, enrolment_no, hostel_required, mobile, name, programme)
    values
        (?, ?, ?, ?, ?, ?, ?, ?, ?)

The result page reads Application saved. Database id: 3 followed by the table of values and Enrolment no: pending approval. The MySQL query returns the new row with id = 3.

Explanation

Two objects, two jobs. AdmissionForm is shaped like the screen (a List of ticked courses, a Boolean that may be null before validation). Student is shaped like the table (one comma-separated courses column, an id). toStudent() is the binding between them: one setter per field, plus String.join for the list.
Spring binds the request to the form object first (data binding), validates it (@Valid), and only then does the code bind the form to the entity. A bad request never reaches the entity or the database.
BindingResult must be the parameter immediately after the @Valid one. If it is missing, Spring throws MethodArgumentNotValidException instead of letting the controller re-render the form.
repo.save() runs inside a transaction (@Transactional on the class). em.persist schedules the INSERT; commit at method exit executes it and MySQL’s auto-increment value is copied into student.getId().
The manual’s Thymeleaf example binds the form straight to the entity class. That works when the two shapes coincide; the separate form object is the pattern that survives Session 6, where Student gains relations.

Question 23

Problem Statement

Write in lab record

Configure Bootstrap in Spring MVC and use default styling classes in the form and view created in the above exercises.

Solution

Write in lab record

Steps

Create WEB-INF/views/head.jspf with the Bootstrap 5.3 CDN link (copy the link tag from getbootstrap.com; the integrity attribute is optional and can be pasted from there).
In every JSP replace the meta lines inside head with <%@ include file="head.jspf" %>. admission-form.jsp and admission-result.jsp from Q21 and Q22 already do this; replace home.jsp with the version below.
Rebuild and reload. The form is centred in a card, inputs have rounded borders, the submit button is blue. A missing link (typo in the URL) shows the unstyled Session 4 look, which is the quickest way to confirm the CDN line is loading.
The WebJar alternative from the manual: add org.webjars:bootstrap:5.3.3 and org.webjars:webjars-locator-core to the pom and link /webjars/bootstrap/css/bootstrap.min.css; the CDN needs no Maven change so it is used here.

Program

Lab record: every tab is one file of the answer. Write all of them.

WEB-INF/views/head.jspfhtml

<%-- /WEB-INF/views/head.jspf : shared <head> contents, pulled in with <%@ include %> --%>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css" rel="stylesheet">
<link href="${pageContext.request.contextPath}/css/admission.css" rel="stylesheet">
<%-- ponytail: no Bootstrap JS bundle; add the script tag when a dropdown or modal appears --%>

WEB-INF/views/home.jsphtml

<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
  <%@ include file="head.jspf" %>
  <title>Student Admission</title>
</head>
<body>
<nav class="navbar navbar-dark"><div class="container"><span class="navbar-brand">IGNOU Student Admission</span></div></nav>
<div class="container">
  <div class="card card-form text-center">
    <div class="card-body">
      <h1 class="h3 card-title">Welcome to the Lab Project for Student Admission using Spring MVC</h1>
      <p class="text-muted">Spring Framework ${springVersion} &middot; server time ${now}</p>
      <a class="btn btn-primary btn-lg" href="${pageContext.request.contextPath}/admission">Apply for admission</a>
      <a class="btn btn-outline-secondary btn-lg" href="${pageContext.request.contextPath}/students">View students</a>
    </div>
  </div>
</div>
</body>
</html>

Output

Expected, checked by reading, not executed: a dark navigation bar with “IGNOU Student Admission”, below it a white card 760 px wide holding the form in two columns (email beside mobile, date beside programme), inline Yes/No radios, stacked course checkboxes, and a right-aligned Cancel / Submit pair. Invalid fields get a red border and red text underneath. The result page shows a green “Application saved” alert and a striped table.

Explanation

Bootstrap is only a stylesheet. Configuring it in Spring MVC means one link tag reaches every page; the jspf include keeps that tag in one file, so a version bump is one edit.
Classes used, all Bootstrap defaults: layout container, row g-3, col-12, col-md-6; form controls form-label, form-control, form-select, form-check, form-check-inline, form-check-input; validation is-invalid, invalid-feedback; components card, card-body, navbar, alert alert-success, table table-striped, btn btn-primary, btn-outline-secondary.
Spring form tags take cssClass instead of class (and cssErrorClass for the error state); plain HTML elements in the same page use class as usual.
No Bootstrap JavaScript is included because nothing on these pages needs it; add the bundle script tag when a dropdown menu or modal appears.

Question 24

Problem Statement

Write in lab record

Apply custom Styling to your pages in Spring MVC.

Solution

Write in lab record

Steps

Create src/main/webapp/css/admission.css (outside WEB-INF, so the browser can fetch it).
Replace WebConfig.java with the version that adds a resource handler for /css/**. Without it the DispatcherServlet, mapped on /, tries to find a controller for /css/admission.css and returns 404.
head.jspf already links /css/admission.css after Bootstrap, so the custom rules win over Bootstrap’s on equal specificity.
Rebuild, hard-reload (Ctrl+Shift+R) and open http://localhost:8080/student-admission/css/admission.css directly to confirm it is served.

Program

Lab record: every tab is one file of the answer. Write all of them.

webapp/css/admission.csscss

/* src/main/webapp/css/admission.css : custom styling on top of Bootstrap */
:root {
  --ignou-maroon: #7b1e3c;
  --ignou-sand: #f6f1ea;
}

body {
  background: var(--ignou-sand);
}

.navbar {
  background: var(--ignou-maroon);
}

.card-form {
  max-width: 760px;
  margin: 2rem auto;
  border: 0;
  box-shadow: 0 0.5rem 1rem rgba(0, 0, 0, 0.08);
}

.card-title {
  color: var(--ignou-maroon);
  border-bottom: 2px solid var(--ignou-maroon);
  padding-bottom: 0.5rem;
  margin-bottom: 1.25rem;
}

.btn-primary {
  background: var(--ignou-maroon);
  border-color: var(--ignou-maroon);
}

.btn-primary:hover {
  background: #5d1630;
  border-color: #5d1630;
}

/* red asterisk after every mandatory label */
label.required::after {
  content: " *";
  color: #dc3545;
}

/* the lab record is printed: hide navigation, keep the data */
@media print {
  .navbar, .btn { display: none; }
  .card-form { box-shadow: none; max-width: none; margin: 0; }
}

WebConfig.javajava

package com.ignou.lab.admission;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.view.InternalResourceViewResolver;

@Configuration
@EnableWebMvc
@ComponentScan("com.ignou.lab.admission")
public class WebConfig implements WebMvcConfigurer {

    @Bean
    public InternalResourceViewResolver viewResolver() {
        return new InternalResourceViewResolver("/WEB-INF/views/", ".jsp");
    }

    /** Q24: /css/** is served from src/main/webapp/css instead of going to a controller. */
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/css/**").addResourceLocations("/css/");
    }
}

Output

Expected, checked by reading, not executed: sand-coloured page background, maroon navigation bar and maroon primary buttons instead of Bootstrap blue, card title underlined in maroon, a red asterisk after each mandatory label, and in print preview (Ctrl+P) the navigation bar and buttons disappear while the form data stays.

Explanation

addResourceHandlers maps a URL pattern to a location inside the WAR; Spring serves the file with caching headers and never involves a controller.
Custom CSS overrides by cascade order: same selector specificity, loaded later, wins. .btn-primary and .navbar redefine Bootstrap’s colours; the :root variables keep the brand colour in one place.
label.required::after adds the asterisk from CSS, so the JSP only sets a class; the mandatory marker cannot drift from the required attribute if both come from the same template line.
The @media print block exists because the lab record is printed; hiding navigation is the difference between a page and a form.

Viva Questions

Do not copy. Read for understanding and the viva

Q: Why validate on both client and server? A: Client checks give instant feedback; the server check is the only one that cannot be bypassed (disable JavaScript, use curl, edit the DOM).
Q: What does @Valid do? A: Tells Spring to run Bean Validation on the bound object before calling the handler and to record violations in the following BindingResult.
Q: What happens if BindingResult is not the next parameter? A: Spring throws the validation exception and the user sees an error page instead of the form with messages.
Q: Difference between @NotNull, @NotEmpty and @NotBlank? A: @NotNull rejects null; @NotEmpty also rejects empty strings or collections; @NotBlank also rejects whitespace-only strings.
Q: Why a separate form object instead of binding to the entity? A: The screen and the table have different shapes; the form object carries validation rules and screen-only fields without polluting the entity.
Q: Why does the CSS file live outside WEB-INF? A: Anything under WEB-INF is never served directly; a stylesheet must be fetched by the browser.
Q: CDN or WebJar for Bootstrap? A: CDN: no build change, browser may already have it cached, needs internet. WebJar: version pinned in the pom, works offline.

Common Mistakes

Do not copy. Read for understanding and the viva

Adding validation annotations and forgetting @Valid on the parameter; every submission passes.
Testing only in the browser and concluding the server rules work. Bypass the browser once (novalidate) to see them.
Writing class="form-control" on a form:input tag; the attribute is cssClass.
Mapping /css/** but putting the folder under WEB-INF; the resource handler cannot serve it.
Loading the custom stylesheet before Bootstrap, so Bootstrap overrides the custom colours.

Session Summary

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Question 21: HTML5 attributes on the form plus Bean Validation on AdmissionForm, messages rendered with form:errors
Question 22: @Valid and BindingResult in AdmissionController, toStudent() binding the form to the Student entity, StudentRepository.save() inserting the row
Question 23: Bootstrap 5.3 from the CDN through head.jspf, default classes on the form, result and home pages
Question 24: admission.css served through a resource handler, brand colours, required-field marker and print rules