Spring supports Bean Validation 1.1 (JSR-303/349/380) to validate object fields declaratively.
Check out Bean validation tutorial.
Also check out Spring Core validation tutorial.
In Spring MVC, if Bean Validation is present on the classpath  e.g. Hibernate Validator, the LocalValidatorFactoryBean is implicitly registered as a global Validator for use with @Valid and Validated on controller method arguments.
Example
Let's modify our last example to show validation errors in the registration page.
Backing Object with Bean Validation constraints annotations
import org.hibernate.validator.constraints.Email;
import org.hibernate.validator.constraints.NotEmpty;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;
public class User {
private Long id;
@Size(min = 5, max = 20)
private String name;
@Size(min = 6, max = 15)
@Pattern(regexp = "\\S+", message = "Spaces are not allowed")
private String password;
@NotEmpty
@Email
private String emailAddress;
//getters and setters
}
The two annotations we used above are Hibernate specific custom JSR-349 compliant annotations: Email and NotEmpty. (In JSR 380 @Email and @NotEmpty are part of Bean validation specifications, check out all predefined constraint annotations here )
The Controller
@Controller
@RequestMapping("/register")
public class UserRegistrationController {
@Autowired
private UserService userService;
@RequestMapping(method = RequestMethod.GET)
public String handleGetRequest () {
return "user-registration";
}
@RequestMapping(method = RequestMethod.POST)
public String handlePostRequest (@Valid User user, BindingResult bindingResult,
Model model) {
if (bindingResult.hasErrors()) {
populateError("name", model, bindingResult);
populateError("emailAddress", model, bindingResult);
populateError("password", model, bindingResult);
return "user-registration";
}
userService.saveUser(user);
return "registration-done";
}
private void populateError (String field, Model model, BindingResult bindingResult) {
if (bindingResult.hasFieldErrors(field)) {
model.addAttribute(field + "Error", bindingResult.getFieldError(field)
.getDefaultMessage());
}
}
What is @Valid annotation?
This is JSR-349 specific annotation. The annotation @Valid used on instance or parameter marks it to be validated by the framework. In above example Spring will invoke the configured Validator instance on User instance before calling the handler method handlePostRequest. In our example the configured Validator is Hibernate Validator, the reference implementation of JSR-349.
What is BindingResult?
org.springframework.validation.BindingResult is a general interface that represents binding results. One of it's feature is to contain validation error information.
In our example we are populating field errors into Model to show errors in the registration page. We have a better alternative which is to use spring-form JSP Tag Library. We will cover that in the next tutorial.
The BindingResult parameter has to follow the model object that is being bound immediately as the method signature might have more than one model object and Spring will create a separate BindingResult instance for each of them.
In our example above 'bindingResult' parameter is used immediately after 'user' parameter.
If you don't follow this rule you will have 400 error code message 'The request sent by the client was syntactically incorrect'.
user-registration.jsp
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<html>
<head>
<style>
span.error {
color: red;
}
</style>
</head>
<body>
<h3> Registration Form <h3>
<br/>
<form action="register" method="post" >
<pre>
Name <input type="text" name="name" value="${user.name}" />
<span class="error">${nameError}</span>
Email address <input type="text" name="emailAddress" value="${user.emailAddress}" />
<span class="error">${emailAddressError}</span>
Password <input type="password" name="password" value="${user.password}" />
<span class="error">${passwordError}</span>
<input type="submit" value="Submit" />
</pre>
</form>
</body>
</html>
Example Project
To test controllers run the unit tests in RegistrationControllerTest.
Or you can run the app using embedded tomcat:
mvn clean install tomcat7:run-war
Use this URL in your browser :
http://localhost:8080/spring-form-validation/register Dependencies and Technologies Used: - Spring Web MVC 4.2.4.RELEASE: Spring Web MVC.
- Spring TestContext Framework 4.2.4.RELEASE: Spring TestContext Framework.
- Java Servlet API 3.0.1
- Hibernate Validator Engine 5.2.4.Final: Hibernate's Bean Validation (JSR-303) reference implementation.
- JUnit 4.12: JUnit is a unit testing framework for Java, created by Erich Gamma and Kent Beck.
- JDK 1.8
- Maven 3.0.4
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