As we mentioned here, redirect is a useful trick to avoid submitting same form multiple times. As a result of URL redirection client receives the result page with a different HTTP request, idealy with a GET method. The browser address bar shows a different URL instead the original form URL. If user refreshes the same page multiple times he/she will not issue another post submission.
In this complete example of 'user registration' we are going to demonstrate how we can achieve that.
Create the backing/command object
public class User implements Serializable{
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
}
In above backing object we used JSR 349 constraints annotations.
The Controller
@Controller
@RequestMapping
public class UserRegistrationController {
@Autowired
private UserService userService;
//shows the empty form with get request
@RequestMapping(value = "register", method = RequestMethod.GET)
public String handleGetRequest (Model model) {
model.addAttribute("user", new User());
return "user-registration";
}
//form post handler which redirect to other URL with GET method
@RequestMapping(value = "register", method = RequestMethod.POST)
public String handlePostRequest (@Valid @ModelAttribute("user") User user,
BindingResult bindingResult,
RedirectAttributes ra) {
if (bindingResult.hasErrors()) {
return "user-registration";
}
userService.saveUser(user);
ra.addFlashAttribute("user", user);
return "redirect:/registration-success";
}
//redirected handler
@RequestMapping(value = "registration-success", method = RequestMethod.GET)
public String handleRegistrationDone(@ModelAttribute("user") User user){
System.out.println("user....: "+user);
return "registration-done";
}
}
In above example we used RedirectAttributes#addFlashAttribute. Please see our last example for more details about that.
user-registration.jsp
<%@taglib uri="http://www.springframework.org/tags/form" prefix="frm"%>
<html>
<head>
<style>
.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>
registration-done.jsp
<%@ page language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<html>
<body>
<h3> Registration done </h3>
<p>User Name: ${user.name}</p>
<p>User email: ${user.emailAddress}
</body>
</html>
Example ProjectDependencies 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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