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Form Handling & Validation

In Spring MVC, form handling and validation are essential for managing user input effectively and ensuring data integrity.

Form Handling in Spring MVC

Form handling allows us to capture data from HTML forms and bind it to Java objects (command objects). This process helps map user input to a Java class, enabling easy handling of form submissions.

Steps to handle a form in Spring MVC

Create a Form Object: Define a Java class with fields that represent the form data.
Define a Controller Method: This method will handle the form submission and use the @ModelAttribute annotation to bind form data to the object.
Create a Form in HTML: Use standard HTML form tags, and ensure that the form fields have names matching the object properties.

Example

public class User {

private String name;

private String email;

// getters and setters

}

@Controller

public class UserController {

@GetMapping("/userForm")

public String showForm(Model model) {

model.addAttribute("user", new User());

return "userForm";

}

@PostMapping("/submitForm")

public String submitForm(@ModelAttribute("user") User user) {

// handle form submission

return "formSuccess";

}

<label for="email">Email:</label>

<button type="submit">Submit</button>

</form>

Form Validation in Spring MVC

To validate the form data, Spring MVC integrates with Java’s Bean Validation API (JSR 303) and Hibernate Validator. You can use annotations like @NotNull, @Size, @Email, etc., on your form object fields to enforce constraints.

Steps for validation

Add Validation Annotations: Annotate the fields in your form object class.
Use @Valid in Controller: In your controller method, use @Valid to trigger the validation and BindingResult to capture validation errors.

Example

import javax.validation.constraints.Email;

import javax.validation.constraints.NotNull;

import javax.validation.constraints.Size;

public class User {

@NotNull

@Size(min = 1, message = "Name cannot be empty")

private String name;

@NotNull

@Email(message = "Please provide a valid email address")

private String email;

// getters and setters

}

@Controller

public class UserController {

@PostMapping("/submitForm")

public String submitForm(@Valid @ModelAttribute("user") User user, BindingResult result) {

if (result.hasErrors()) {

return "userForm"; // return to form page if there are validation errors

}

// handle form submission if valid

return "formSuccess";

}

Displaying Validation Errors

Spring MVC allows you to easily display validation errors on the form. You can use BindingResult to check for errors and display them in the JSP/HTML view.

Example in JSP

<span style="color: red">${#fields.hasErrors('name') ? #fields.errors('name') : ''}</span>