In our last example we saw how to do field validation declaratively using bean validation API.
We can simplify our code a little more on the view side by using Spring Form JSP Tag Library.
Among many things, Spring Tag Library provides JSP tags to render validation errors implicitly.
Let's modify our last example one more time to see how that works.
user-registration.jsp
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@taglib uri="http://www.springframework.org/tags/form" prefix="frm"%>
<html>
<head>
<style>
span.error {
color: red;
}
</style>
</head>
<body>
<h3> Registration Form <h3>
<br/>
<frm:form action="register" method="post" commandName="user">
<pre>
Name <frm:input path="name" />
<frm:errors path="name" cssClass="error" />
Email address <frm:input path="emailAddress" />
<frm:errors path="emailAddress" cssClass="error" />
Password <frm:password path="password" />
<frm:errors path="password" cssClass="error" />
<input type="submit" value="Submit" />
</pre>
</frm:form>
</body>
</html>
In above code, spring form tag is implicitly mapping the backing object fields to the HTML form fields and also taking care of the validation errors via frm:errors.
One more important thing to understand is that, Spring top level form tag must have to specify 'commandName' (or 'modelAttribute', there's no difference between the two) which is actually the name of the 'model attribute' under which the form object is exposed. That also means we are required to use annotation @ModelAttribute on our backing object using the same name as 'commandName'. Please see our controller next.
The Controller
Comparing with our last example our controller has become simpler.
@Controller
@RequestMapping("/register")
public class UserRegistrationController {
@Autowired
private UserService userService;
@RequestMapping(method = RequestMethod.GET)
public String handleGetRequest (Model model) {
model.addAttribute("user", new User());
return "user-registration";
}
@RequestMapping(method = RequestMethod.POST)
public String handlePostRequest (@Valid @ModelAttribute("user") User user,
BindingResult bindingResult, Model model) {
if (bindingResult.hasErrors()) {
return "user-registration";
}
userService.saveUser(user);
return "registration-done";
}
}
Notice, in above handler method we must use @ModelAttribute with a name matching with 'commandName' in our jsp form.
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-tag-lib/register
The expected output of this example is same as our last example. 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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