The Registration API becomes RESTful

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This article is part of a series:

• Spring Security Registration Series
• The Registration Process With Spring Security
• Registration – Activate a New Account by Email
• Spring Security Registration – Resend Verification Email
• Registration with Spring Security – Password Encoding

• The Registration API becomes RESTful (current article)

• Spring Security – Reset Your Password
• Registration – Password Strength and Rules
• Updating Your Password
• Notify User of Login From New Device or Location

1. Overview

In the last few articles of the Registration series here on Baeldung, we built most of the functionality we needed in an MVC fashion.

We’re now going to transition some of these APIs to a more RESTful approach.

2. The Register Operation

Let’s start with the main Register operation:

@PostMapping("/user/registration")
public GenericResponse registerUserAccount(
      @Valid UserDto accountDto, HttpServletRequest request) {
    logger.debug("Registering user account with information: {}", accountDto);
    User registered = createUserAccount(accountDto);
    if (registered == null) {
        throw new UserAlreadyExistException();
    }
    String appUrl = "http://" + request.getServerName() + ":" + 
      request.getServerPort() + request.getContextPath();
   
    eventPublisher.publishEvent(
      new OnRegistrationCompleteEvent(registered, request.getLocale(), appUrl));

    return new GenericResponse("success");
}

So, how is this different from the original MVC implementation?

Here goes:

the request is now correctly mapped to an HTTP POST
we’re now returning a proper DTO and marshaling that directly into the body of the response
we’re no longer dealing with error handling in the method at all

We’re also removing the old showRegistrationPage() – as that’s not needed to simply display the registration page.

3. The registration.html

Furthermore, we need to modify the registration.html to:

use Ajax to submit the registration form
receive the results of the operation as JSON

Here goes:

<html>
<head>
<title th:text="#{label.form.title}">form</title>
</head>
<body>
<form method="POST" enctype="utf8">
    <input  name="firstName" value="" />
    <span id="firstNameError" style="display:none"></span>
 
    <input  name="lastName" value="" />
    <span id="lastNameError" style="display:none"></span>
                     
    <input  name="email" value="" />           
    <span id="emailError" style="display:none"></span>
     
    <input name="password" value="" type="password" />
    <span id="passwordError" style="display:none"></span>
                 
    <input name="matchingPassword" value="" type="password" />
    <span id="globalError" style="display:none"></span>
 
    <a href="#" onclick="register()" th:text="#{label.form.submit}>submit</a>
</form>
             
 
<script src="jquery.min.js"></script>
<script type="text/javascript">
var serverContext = [[@{/}]];

function register(){
    $(".alert").html("").hide();
    var formData= $('form').serialize();
    $.post(serverContext + "/user/registration",formData ,function(data){
        if(data.message == "success"){
            window.location.href = serverContext +"/successRegister.html";
        }
    })
    .fail(function(data) {
        if(data.responseJSON.error.indexOf("MailError") > -1)
        {
            window.location.href = serverContext + "/emailError.html";
        }
        else if(data.responseJSON.error.indexOf("InternalError") > -1){
            window.location.href = serverContext + 
              "/login.html?message=" + data.responseJSON.message;
        }
        else if(data.responseJSON.error == "UserAlreadyExist"){
            $("#emailError").show().html(data.responseJSON.message);
        }
        else{
            var errors = $.parseJSON(data.responseJSON.message);
            $.each( errors, function( index,item ){
                $("#"+item.field+"Error").show().html(item.defaultMessage);
            });
            errors = $.parseJSON(data.responseJSON.error);
            $.each( errors, function( index,item ){
                $("#globalError").show().append(item.defaultMessage+"<br>");
            });
 }
}
</script>
</body>
</html>

4. Exception Handling

Generally, implementing a good exception-handling strategy can make the REST API more robust and error-prone.

We’re using the same @ControllerAdvice mechanism to deal cleanly with different exceptions – and now we need a new type of exception.

This is the BindException – which is thrown when the UserDto is validated (if invalid). We’ll override the default ResponseEntityExceptionHandler method handleBindException() to add the errors in the response body:

@Override
protected ResponseEntity<Object> handleBindException
  (BindException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
    logger.error("400 Status Code", ex);
    BindingResult result = ex.getBindingResult();
    GenericResponse bodyOfResponse = 
      new GenericResponse(result.getFieldErrors(), result.getGlobalErrors());
    
    return handleExceptionInternal(
      ex, bodyOfResponse, new HttpHeaders(), HttpStatus.BAD_REQUEST, request);
}

Next, we will also need to handle our custom Exception UserAlreadyExistException – which is thrown when the user registers with an email that already exists:

@ExceptionHandler({ UserAlreadyExistException.class })
public ResponseEntity<Object> handleUserAlreadyExist(RuntimeException ex, WebRequest request) {
    logger.error("409 Status Code", ex);
    GenericResponse bodyOfResponse = new GenericResponse(
      messages.getMessage("message.regError", null, request.getLocale()), "UserAlreadyExist");
    
    return handleExceptionInternal(
      ex, bodyOfResponse, new HttpHeaders(), HttpStatus.CONFLICT, request);
}

5. The GenericResponse

We also need to improve the GenericResponse implementation to hold these validation errors:

public class GenericResponse {

    public GenericResponse(List<FieldError> fieldErrors, List<ObjectError> globalErrors) {
        super();
        ObjectMapper mapper = new ObjectMapper();
        try {
            this.message = mapper.writeValueAsString(fieldErrors);
            this.error = mapper.writeValueAsString(globalErrors);
        } catch (JsonProcessingException e) {
            this.message = "";
            this.error = "";
        }
    }
}

6. UI – Field and Global Errors

Finally, let’s see how to handle both field and global errors using jQuery:

var serverContext = [[@{/}]];

function register(){
    $(".alert").html("").hide();
    var formData= $('form').serialize();
    $.post(serverContext + "/user/registration",formData ,function(data){
        if(data.message == "success"){
            window.location.href = serverContext +"/successRegister.html";
        }
    })
    .fail(function(data) {
        if(data.responseJSON.error.indexOf("MailError") > -1)
        {
            window.location.href = serverContext + "/emailError.html";
        }
        else if(data.responseJSON.error.indexOf("InternalError") > -1){
            window.location.href = serverContext + 
              "/login.html?message=" + data.responseJSON.message;
        }
        else if(data.responseJSON.error == "UserAlreadyExist"){
            $("#emailError").show().html(data.responseJSON.message);
        }
        else{
            var errors = $.parseJSON(data.responseJSON.message);
            $.each( errors, function( index,item ){
                $("#"+item.field+"Error").show().html(item.defaultMessage);
            });
            errors = $.parseJSON(data.responseJSON.error);
            $.each( errors, function( index,item ){
                $("#globalError").show().append(item.defaultMessage+"<br>");
            });
 }
}

Note that:

If there are validation errors, then the message object contains the field errors and the error object contains global errors
We display each field error next to its field
We display all the global errors in one place at the end of the form

7. Conclusion

The focus of this quick article is to bring the API into a more RESTful direction and show a simple way of dealing with that API in the front end.

The jQuery front end itself is not the focus – just a basic potential client that can be implemented in any number of JS frameworks, while the API remains exactly the same.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.

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