Form Data Binding

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.5</version>
        <relativePath/>
    </parent>

    <groupId>com.example</groupId>
    <artifactId>student-form-binding-demo</artifactId>
    <version>1.0.0</version>
    <name>student-form-binding-demo</name>

    <properties>
        <java.version>17</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

package com.example.formbinding.entity;

import jakarta.persistence.CollectionTable;
import jakarta.persistence.Column;
import jakarta.persistence.ElementCollection;
import jakarta.persistence.Entity;
import jakarta.persistence.FetchType;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.JoinColumn;
import jakarta.persistence.Table;
import org.springframework.format.annotation.DateTimeFormat;

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

// This single class is the Java model the form is bound to (and the database table).
@Entity
@Table(name = "students")
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String name;                 // text input      -> String

    private String email;                // email input     -> String

    private Integer age;                 // number input    -> Integer (type conversion)

    @DateTimeFormat(iso = DateTimeFormat.ISO.DATE)
    @Column(name = "date_of_birth")
    private LocalDate dateOfBirth;       // date input      -> LocalDate (format conversion)

    private String gender;               // radio buttons   -> String (one value)

    private String department;           // drop-down list  -> String (one value)

    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "student_courses", joinColumns = @JoinColumn(name = "student_id"))
    @Column(name = "course")
    private List<String> courses = new ArrayList<>();   // checkboxes -> List<String> (many values)

    @Column(length = 500)
    private String address;              // textarea        -> String

    public Student() {
    }

    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }

    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 Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }

    public LocalDate getDateOfBirth() { return dateOfBirth; }
    public void setDateOfBirth(LocalDate dateOfBirth) { this.dateOfBirth = dateOfBirth; }

    public String getGender() { return gender; }
    public void setGender(String gender) { this.gender = gender; }

    public String getDepartment() { return department; }
    public void setDepartment(String department) { this.department = department; }

    public List<String> getCourses() { return courses; }
    public void setCourses(List<String> courses) { this.courses = courses; }

    public String getAddress() { return address; }
    public void setAddress(String address) { this.address = address; }
}

package com.example.formbinding.repository;

import com.example.formbinding.entity.Student;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface StudentRepository extends JpaRepository<Student, Long> {
}

package com.example.formbinding.service;

import com.example.formbinding.entity.Student;
import com.example.formbinding.repository.StudentRepository;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class StudentService {

    private final StudentRepository studentRepository;

    public StudentService(StudentRepository studentRepository) {
        this.studentRepository = studentRepository;
    }

    public Student register(Student student) {
        return studentRepository.save(student);
    }

    public List<Student> getAll() {
        return studentRepository.findAll();
    }
}

package com.example.formbinding.controller;

import com.example.formbinding.entity.Student;
import com.example.formbinding.service.StudentService;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import java.util.List;

@Controller
@RequestMapping("/students")
public class StudentController {

    private static final List<String> GENDERS = List.of("Male", "Female", "Other");
    private static final List<String> DEPARTMENTS = List.of("CSE", "ECE", "MECH", "CIVIL");
    private static final List<String> COURSES = List.of("Java", "Spring Boot", "SQL", "React", "Python");

    private final StudentService studentService;

    public StudentController(StudentService studentService) {
        this.studentService = studentService;
    }

    // Never let a form submit set the database id
    @InitBinder
    public void initBinder(WebDataBinder binder) {
        binder.setDisallowedFields("id");
    }

    // GET /students/register -> shows the empty form (an empty Student is bound to it)
    @GetMapping("/register")
    public String showForm(Model model) {
        model.addAttribute("student", new Student());
        model.addAttribute("genders", GENDERS);
        model.addAttribute("departments", DEPARTMENTS);
        model.addAttribute("courseOptions", COURSES);
        return "register";
    }

    // POST /students/register -> Spring fills the Student object from the submitted fields
    @PostMapping("/register")
    public String register(@ModelAttribute("student") Student student, RedirectAttributes redirectAttributes) {
        Student saved = studentService.register(student);
        redirectAttributes.addFlashAttribute("message",
                "Student '" + saved.getName() + "' registered successfully with id " + saved.getId());
        return "redirect:/students";
    }

    // POST /students/quick-register -> binding single fields with @RequestParam
    @PostMapping("/quick-register")
    @ResponseBody
    public Student quickRegister(@RequestParam String name,
                                 @RequestParam String email,
                                 @RequestParam(defaultValue = "CSE") String department) {
        Student student = new Student();
        student.setName(name);
        student.setEmail(email);
        student.setDepartment(department);
        return studentService.register(student);
    }

    // GET /students -> HTML table of registered students
    @GetMapping
    public String list(Model model) {
        model.addAttribute("students", studentService.getAll());
        return "students";
    }

    // GET /students/json -> same data as JSON (to verify binding in Postman / browser)
    @GetMapping("/json")
    @ResponseBody
    public List<Student> listJson() {
        return studentService.getAll();
    }
}

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Student Registration</title>
    <style>
        body { font-family: Arial, sans-serif; background: #f4f6f8; margin: 0; padding: 30px; }
        .card { max-width: 560px; margin: auto; background: #fff; padding: 25px 30px; border-radius: 8px;
                box-shadow: 0 2px 8px rgba(0,0,0,.12); }
        h2 { margin-top: 0; }
        label.title { display: block; margin: 14px 0 5px; font-weight: bold; }
        input[type=text], input[type=email], input[type=number], input[type=date], select, textarea {
            width: 100%; padding: 8px; box-sizing: border-box; border: 1px solid #bbb; border-radius: 4px; }
        .inline label { margin-right: 15px; font-weight: normal; }
        button { margin-top: 20px; padding: 10px 22px; background: #2563eb; color: #fff; border: 0;
                 border-radius: 4px; cursor: pointer; font-size: 15px; }
        a { color: #2563eb; }
    </style>
</head>
<body>
<div class="card">
    <h2>Student Registration</h2>

    <!-- th:object binds the whole form to the 'student' model object -->
    <form th:action="@{/students/register}" th:object="${student}" method="post">

        <label class="title">Full Name</label>
        <input type="text" th:field="*{name}" placeholder="Enter name" required>

        <label class="title">Email</label>
        <input type="email" th:field="*{email}" placeholder="Enter email">

        <label class="title">Age</label>
        <input type="number" th:field="*{age}" min="1" max="100">

        <label class="title">Date of Birth</label>
        <input type="date" th:field="*{dateOfBirth}">

        <label class="title">Gender</label>
        <div class="inline">
            <label th:each="g : ${genders}">
                <input type="radio" th:field="*{gender}" th:value="${g}"> <span th:text="${g}"></span>
            </label>
        </div>

        <label class="title">Department</label>
        <select th:field="*{department}">
            <option value="">-- Select Department --</option>
            <option th:each="d : ${departments}" th:value="${d}" th:text="${d}"></option>
        </select>

        <label class="title">Courses</label>
        <div class="inline">
            <label th:each="c : ${courseOptions}">
                <input type="checkbox" th:field="*{courses}" th:value="${c}"> <span th:text="${c}"></span>
            </label>
        </div>

        <label class="title">Address</label>
        <textarea th:field="*{address}" rows="3" placeholder="Enter address"></textarea>

        <button type="submit">Register</button>
    </form>

    <p><a th:href="@{/students}">View registered students</a></p>
</div>
</body>
</html>

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Registered Students</title>
    <style>
        body { font-family: Arial, sans-serif; background: #f4f6f8; margin: 0; padding: 30px; }
        .card { max-width: 1000px; margin: auto; background: #fff; padding: 25px 30px; border-radius: 8px;
                box-shadow: 0 2px 8px rgba(0,0,0,.12); }
        table { width: 100%; border-collapse: collapse; margin-top: 15px; }
        th, td { border: 1px solid #ddd; padding: 8px 10px; text-align: left; font-size: 14px; }
        th { background: #2563eb; color: #fff; }
        .msg { background: #dcfce7; color: #166534; padding: 10px 14px; border-radius: 4px; }
        a { color: #2563eb; }
    </style>
</head>
<body>
<div class="card">
    <h2>Registered Students</h2>

    <div class="msg" th:if="${message}" th:text="${message}"></div>

    <table>
        <thead>
        <tr>
            <th>ID</th><th>Name</th><th>Email</th><th>Age</th><th>Date of Birth</th>
            <th>Gender</th><th>Department</th><th>Courses</th><th>Address</th>
        </tr>
        </thead>
        <tbody>
        <tr th:each="s : ${students}">
            <td th:text="${s.id}"></td>
            <td th:text="${s.name}"></td>
            <td th:text="${s.email}"></td>
            <td th:text="${s.age}"></td>
            <td th:text="${s.dateOfBirth}"></td>
            <td th:text="${s.gender}"></td>
            <td th:text="${s.department}"></td>
            <td th:text="${#strings.listJoin(s.courses, ', ')}"></td>
            <td th:text="${s.address}"></td>
        </tr>
        <tr th:if="${#lists.isEmpty(students)}">
            <td colspan="9">No students registered yet.</td>
        </tr>
        </tbody>
    </table>

    <p><a th:href="@{/students/register}">Register another student</a></p>
</div>
</body>
</html>

package com.example.formbinding;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class StudentFormBindingApplication {

    public static void main(String[] args) {
        SpringApplication.run(StudentFormBindingApplication.class, args);
    }
}