Validating Spring MVC Request Mapping Method parameters

This short post demonstrates how to set up and use JSR-303 Validation for the arguments in Spring MVC request mapping methods for path variable and request parameter arguments. I am using Spring Boot v1.2.5 with Maven 3.

I. MethodValidationPostProcessor

The only configuration needed is adding the MethodValidationPostProcessor (javadoc) bean to the Spring configuration, e.g.

 @Bean
 public MethodValidationPostProcessor methodValidationPostProcessor() {
      return new MethodValidationPostProcessor();
 }

II Add validation to controller request mapping method

First, add the @Validate annotation to the controller class as follows:

@RestController
@Validated
public class HelloController {
     ...

Then add any JSR-303 validation annotation to a request mapping method arguments:

 @RequestMapping("/hi/{name}")
 public String sayHi(@Size(max = 10, min = 3, message = "name should have between 3 and 10 characters") @PathVariable("name") String name) {
      return "Hi " + name;
 }

The example codes above shows how to validate a value in the request path marked by @PathVariable. You can do the same with @RequestParam

III Validation exception handling

A ConstraintViolationException will be thrown if the size of the path variable is not within 3 to 10 characters. You may need to catch this exception and process it using a Spring MVC exception handler, for example to return the error messages in the response:

 @ExceptionHandler(value = { ConstraintViolationException.class })
 @ResponseStatus(value = HttpStatus.BAD_REQUEST)
 public String handleResourceNotFoundException(ConstraintViolationException e) {
      Set<ConstraintViolation<?>> violations = e.getConstraintViolations();
      StringBuilder strBuilder = new StringBuilder();
      for (ConstraintViolation<?> violation : violations ) {
           strBuilder.append(violation.getMessage() + "\n");
      }
      return strBuilder.toString();
 }