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:
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@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:
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@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:
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@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.
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@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:
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@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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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.
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.
Xavier, can you post the XML configuration that shows the component-scan configuration ?
Hi,
You can check the source code at the link provided in the first section, but here's a direct link to the file you asked:
https://github.com/xpadro/spring-rest/blob/master/rest-controlleradvice/src/main/resources/xpadro/spring/rest/configuration/root-context.xml
Regards
make sure you have in your dispath-servlet.
Prou interessant seria fer ús de validation groups, validació de camps més complexos (amb propis validadors) juntament amb anotacions de validació 🙂
Estic d'acord amb tu, potser en un altre post 😉
Gràcies pel comentari!
What is the purpose/responsibility of PersonValidator here… i couldn't find that class also….
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
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 ?
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", 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
Lovely. Ive been wondering how to setup all my property editors in a single place. Your combination of @ControllerAdvice and @InitBinder did the trick
Great Ashario, it's nice to know it helped you.