spring Spring JSR 303 Bean Validation Spring JSR 303 Validation - Customize error messages

Example

Suppose we have a simple class with validation annotations

public class UserDTO {
    @NotEmpty
    private String name;

    @Min(18)
    private int age;

//getters/setters
}

A controller to check the UserDTO validity.

@RestController
public class ValidationController {

    @RequestMapping(value = "/validate", method = RequestMethod.POST)
    public ResponseEntity<String> check(@Valid @RequestBody UserDTO userDTO,
           BindingResult bindingResult) {
        return new ResponseEntity<>("ok" , HttpStatus.OK);
    }
}

And a test.

@Test
public void testValid() throws Exception {
    TestRestTemplate template = new TestRestTemplate();
    String url = base + contextPath + "/validate";
    Map<String, Object> params = new HashMap<>();
    params.put("name", "");
    params.put("age", "10");

    MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
    headers.add("Content-Type", "application/json");

    HttpEntity<Map<String, Object>> request = new HttpEntity<>(params, headers);
    String res = template.postForObject(url, request, String.class);

    assertThat(res, equalTo("ok"));
}

Both name and age are invalid so in the BindingResult we have two validation errors. Each has array of codes.

Codes for Min check

0 = "Min.userDTO.age"
1 = "Min.age"
2 = "Min.int"
3 = "Min"

And for NotEmpty check

0 = "NotEmpty.userDTO.name"
1 = "NotEmpty.name"
2 = "NotEmpty.java.lang.String"
3 = "NotEmpty"

Let's add a custom.properties file to substitute default messages.

@SpringBootApplication
@Configuration
public class DemoApplication {

    @Bean(name = "messageSource")
    public MessageSource messageSource() {
        ReloadableResourceBundleMessageSource bean = new ReloadableResourceBundleMessageSource();
        bean.setBasename("classpath:custom");
        bean.setDefaultEncoding("UTF-8");
        return bean;
    }

    @Bean(name = "validator")
    public LocalValidatorFactoryBean validator() {
        LocalValidatorFactoryBean bean = new LocalValidatorFactoryBean();
        bean.setValidationMessageSource(messageSource());
        return bean;
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

If we add to the custom.properties file the line

NotEmpty=The field must not be empty!

The new value is shown for the error. To resolve message validator looks through the codes starting from the beginning to find proper messages.

Thus when we define NotEmpty key in the .properties file for all cases where the @NotEmpty annotation is used our message is applied.

If we define a message

Min.int=Some custom message here.

All annotations where we app min check to integer values use the newly defined message.

The same logic could be applied if we need to localize the validation error messages.