Centralize validation and exception handling with @ControllerAdvice

1 Introduction

The ControllerAdvice annotation introduced by Spring 3.2 allows us to handle several functionalities in a way that can be shared by all controllers (through its handler methods, annotated with @RequestMapping). This annotation is mainly used to define the following methods:
  • @ExceptionHandler: Handles exceptions thrown by handler methods.
  • @InitBinder: Initializes the WebDataBinder, which will be used to populate objects passed as arguments to the handler methods. Usually, it is used to register property editors or validators.
  • @ModelAttribute: Binds a parameter or return value to an attribute, which will then be exposed to a web view.
Source code can be found at github.

2 Adding validation and exception handling

The following is a description of  the controller’s handler methods before implementing the @ControllerAdvice.
Add person controller:

@RequestMapping(value="/persons", method=RequestMethod.POST)
@ResponseStatus(HttpStatus.CREATED)
public void addPerson(@Valid @RequestBody Person person, HttpServletRequest request, HttpServletResponse response) {
    personRepository.addPerson(person);
    logger.info("Person added: "+person.getId());
    response.setHeader("Location", request.getRequestURL().append("/").append(person.getId()).toString());
}

@InitBinder
public voidinitBinder(WebDataBinder binder) {
    binder.setValidator(new PersonValidator());
}

@ExceptionHandler({MethodArgumentNotValidException.class})
publicResponseEntity<String> handleValidationException(MethodArgumentNotValidException pe) {
    return new ResponseEntity<String>(pe.getMessage(), HttpStatus.BAD_REQUEST);
}

 

Besides the handler method, this controller has the following methods:
  • initBinder: Registers a validator to prevent that a person with invalid data is introduced. To make the validator validate the person object passed as a parameter, it is necessary to add the @Valid annotation to the argument. Spring 3 fully supports JSR-303 bean validation API, but it does not implement it. The reference implementation which is used in this example is Hibernate Validator 4.x.
  • handleValidationException: Handles the MethodArgumentNotValidException that can be thrown by the handler method. This exception is thrown by Spring MVC when an argument annotated with @Valid, fails its validation.

Get person controller:
@RequestMapping(value="/persons/{personId}", method=RequestMethod.GET)
public @ResponseBody Person getPerson(@PathVariable("personId") long id) {
    return personRepository.getPerson(id);
}

@ExceptionHandler({PersonNotFoundException.class})
publicResponseEntity<String> handlePersonNotFound(PersonNotFoundException pe) {
    return newResponseEntity<String>(pe.getMessage(), HttpStatus.NOT_FOUND);
}

 

This controller adds an exception handler for handling when a request asks to retrieve a person that does not exist.



Update person controller:
@RequestMapping(value="/persons", method=RequestMethod.PUT)
@ResponseStatus(HttpStatus.CREATED)
public void updatePerson(@Valid @RequestBody Person person, HttpServletRequest request, HttpServletResponse response) {
    personRepository.updatePerson(person);
    logger.info("Person updated: "+person.getId());
    response.setHeader("Location", request.getRequestURL().append("/").append(person.getId()).toString());
}

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.setValidator(new PersonValidator());
}

@ExceptionHandler({PersonNotFoundException.class})
public ResponseEntity<String> handlePersonNotFound(PersonNotFoundException pe) {
    return newResponseEntity<String>(pe.getMessage(), HttpStatus.NOT_FOUND);
}

@ExceptionHandler({Exception.class})
public ResponseEntity<String> handleValidationException(MethodArgumentNotValidException pe) {
    return newResponseEntity<String>(pe.getMessage(), HttpStatus.BAD_REQUEST);
}

 

We are repeating code, since @ExceptionHandler is not global.

3 Centralizing code

ControllerAdvice annotation is itself annotated with @Component. Hence, the class that we are implementing will be autodetected through classpath scanning.

@ControllerAdvice
public classCentralControllerHandler {
@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.setValidator(new PersonValidator());
}

@ExceptionHandler({PersonNotFoundException.class})
public ResponseEntity<String> handlePersonNotFound(PersonNotFoundException pe) {
    return newResponseEntity<String>(pe.getMessage(), HttpStatus.NOT_FOUND);
}

@ExceptionHandler({MethodArgumentNotValidException.class})
public ResponseEntity<String> handleValidationException(MethodArgumentNotValidException pe) {
    return newResponseEntity<String>(pe.getMessage(), HttpStatus.BAD_REQUEST);
}
}

Finally, we can delete these methods from the controllers, taking rid of code duplication, since this class will handle exception handling and validation for all handler methods annotated with @RequestMapping.

 

4 Testing

The methods described below, test the retrieval of persons:

@Test
public void getExistingPerson() {
    String uri = "http://localhost:8081/rest-controlleradvice/spring/persons/{personId}";
    Person person = restTemplate.getForObject(uri, Person.class, 1l);
    assertNotNull(person);
    assertEquals("Xavi", person.getName());
}

@Test
public void getNonExistingPerson() {
    String uri = "http://localhost:8081/rest-controlleradvice/spring/persons/{personId}";
    try {
        restTemplate.getForObject(uri, Person.class, 5l);
        throw new AssertionError("Should have returned an 404 error code");
    } catch(HttpClientErrorException e) {
        assertEquals(HttpStatus.NOT_FOUND, e.getStatusCode());
    }
}

 

The rest of tests can be found with the source code linked above.

 

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13 thoughts on “Centralize validation and exception handling with @ControllerAdvice

  1. When I put the @ExceptionHandler in the controller class, it works fine but when I am removing it and putting in the class annotated with @ControllerAdvice..it does not reach in this exception handler method. Do I have to do anything specific to load Controller Advice class other than component scan config which I already have.

  2. You don't need to do anything else. Are you sure that the package of the @ControllerAdvice annotated class is located within the component scan path? Also check if the exception captured by the exception handler is the same as the one being thrown by the @RequestMapping method.

  3. Prou interessant seria fer ús de validation groups, validació de camps més complexos (amb propis validadors) juntament amb anotacions de validació 🙂

  4. Hi Manish,

    The purpose of PersonValidator is to prevent an invalid person to be introduced. Check initBinder description in section 2 of this post. The class is not shown here because the validation implementation is not the central point of this post. However, if you want to check it, you can take a look at the source code provided at the beginning. Here's a direct link to the requested validator class:
    https://github.com/xpadro/spring-rest/tree/master/rest-controlleradvice/src/main/java/xpadro/spring/rest/validator

  5. Nice and clean example. It seems with SpringMVC there are many different ways to achieve the same result. What is your opinion on returning a ResponseEntity from your getPerson method instead of @ResponseBody Person ?

  6. Hi Andre,

    Thanks for your feedback, I appreciate it. About your question, I'm returning a @ResponseBody because I just want access to the response body. If you see the test example at section 4, returning @ResponseBody plus using message converters allows us to receive a Person instance directly in our test class.

    I would use @ResponseEntity if I wanted more control and needed access to response headers in addition to the body. Check the following example:

    ResponseEntity entity = template.getForEntity("http://example.com&quot;, String.class);
    String body = entity.getBody();
    MediaType contentType = entity.getHeaders().getContentType();
    HttpStatus statusCode = entity.getStatusCode();

    The above example is taken from http://docs.spring.io/spring/docs/3.0.x/api/org/springframework/http/ResponseEntity.html

  7. Lovely. Ive been wondering how to setup all my property editors in a single place. Your combination of @ControllerAdvice and @InitBinder did the trick

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