How to handle repository exception in the controller - spring mvc - spring

Question

i'm using spring boot and spring MVC. I'm creating a simple form(CRUD)
here is the code:
#Document
public class User
{
#Id
private ObjectId id;
#Indexed(unique=true)
#NotNull
#Size(min=2, max=30)
private String username;
#NotNull
#Size(min=2, max=30)
private String password;
private List<String> roles;
...
Controller:
#Controller
#RequestMapping("/admin")
public class AdminController {
...
/**
* NEW USER (POST)
*/
#RequestMapping(value = "new", method = RequestMethod.POST)
public ModelAndView newUser(#Valid User user, BindingResult bindingResult) {
if (bindingResult.hasErrors()) {
return new ModelAndView("/admin/new");
}
user.setRoles(Arrays.asList(Constants.ROLE_ADMIN));
ur.save(user);
return new ModelAndView("redirect:/admin");
}
/**
* NEW USER (VIEW)
*/
#RequestMapping(value = "new", method = RequestMethod.GET)
public ModelAndView newUser(User user) {
ModelAndView mv = new ModelAndView("admin/new");
return mv;
}
...
}
and the View:
<form name="new" th:action="#{/admin/new}" th:object="${user}" method="post">
<table>
<tr th:if="${error != null}">
<td colspan="4">
<span th:text="${error}"></span>
</td>
</tr>
<tr>
<td>Name:</td>
<td><input type="text" name="username" autocomplete="off"/></td>
<td width="10"/>
<td th:if="${#fields.hasErrors('username')}" th:errors="*{username}"></td>
</tr>
<tr>
<td>Password:</td>
<td><input type="password" name="password" autocomplete="off"/></td>
<td width="10"/>
<td th:if="${#fields.hasErrors('password')}" th:errors="*{password}"></td>
</tr>
<tr>
<td><button type="submit">Create</button></td>
</tr>
</table>
</form>
and it works, if I put an username bigger than 30 character.
But if I got and exception from the repository, for example:
DuplicateKey from the mongodb repository, didn't work.
So i tried to put this code in the controller:
#ExceptionHandler(Exception.class)
public ModelAndView handleCustomException(Exception ex) {
ModelAndView model = new ModelAndView("admin/new");
model.addObject("error", ex.getMessage());
return model;
}
It handle all the exceptions, but in this moment I don't have the "User" or "BindingResult" and when it try to render gets this error:
2015-09-22 13:36:55.498 ERROR 6208 --- [nio-8080-exec-8] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "#fields.hasErrors('username')" (admin/new:21)] with root cause
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'user' available as request attribute
What I'm doing wrong?
How should I handle this kind of exception?
There is a way to send the USER to ExceptionHandler?
Thanks.

Answer 1

Because you don't have to return admin/new from the error handler. The view is expecting the User object that you are correctly populating in normal controllers. In case of an error this object simply isn't there. So, return another view from the error controller: ModelAndView model = new ModelAndView("admin/error"); for example.
Anyhow, this is not a solution. You need to catch exceptions. In this situation it is always better to have an intermediate layer called Service. In service you can catch any repository exceptions and decide what to do about them.