[FIXED] Reject fractional values in int fields in a Spring Boot REST request

Issue

Controller method:

@PostMapping(value = "/template")
ResponseEntity<Object> createtemplate(@Valid @RequestBody Template template) {
        return templateService.createCsvTemplate(template);
}

Object class:

@Getter
@Setter
public class Template {  
    @Min(value = 1, message = "Please provide a valid ID, must be greater than 0")
    private int id;
}

POST input:

{
    "id": 5.5
}

The application accepts this value, setting the value of id to 5. How can I reject accepting such fractional values, throwing an error when one is received?

Solution

By default, jackson serializes decimal value as integer because ACCEPT_FLOAT_AS_INT flag is true by default. Set ACCEPT_FLOAT_AS_INT to false should fix your problem. And your need to handle throwing exception also.

ObjectMapper.configure(DESERIALIZATION_FEATURE.ACCEPT_FLOAT_AS_INT, false);

You can set configuration this way

@Configuration
public class JacksonConfig {

  @Bean
  @Primary
  public ObjectMapper configureObjectMapper() {
    ObjectMapper mapper = new ObjectMapper();
    mapper.configure(DESERIALIZATION_FEATURE.ACCEPT_FLOAT_AS_INT, false);
    return mapper;
  }

}

Answered By - Eklavya
Answer Checked By - Timothy Miller (JavaFixing Admin)