with the Error Handling Spring Boot Starter library. We look at a  project that improves on the default Spring boot error handling for REST APIs.

According the project's definition this project sets out:

to make it easy to have proper and consistent error responses

or in other words to fix what's wrong with the default Spring Boot error handling. Which is :

1) Exceptions throw an empty body when @WebMvcTest is in place because

Spring Boot's error handling is based on Servlet container error mappings that result in an ERROR dispatch to an ErrorController. MockMvc however is container-less testing so with no Servlet container the exception simply bubbles up with nothing to stop it.

A workaround is to go with the alternative of @SpringBootTest
but this is used with integrated testing as such sub-optimal compared to using @WebMvcTest since you've got to summon a full application context.

2) Then, there is no error message in the response that indicates the exact problem. In many cases, the response status alone is not enough to know exactly what is the problem.

3) And finally, the exact validation problems are not shown.

Error Handling Spring Boot Starter gets these issues fixed by adding: 

• Consistent error responses for @WebMvcTest and @SpringBootTest tests.
• Detailed validation errors per property, such as :

  {
    "code": "VALIDATION_FAILED",
    "message": "Validation failed for object='createInfoRequestRequestBody'. Error count: 3",
    "fieldErrors": [
      {
        "code": "REQUIRED_NOT_BLANK",
        "property": "phoneNumber",
        "message": "must not be blank",
        "rejectedValue": null
      },
      {
        "code": "REQUIRED_NOT_BLANK",
        "property": "email",
        "message": "must not be blank",
        "rejectedValue": null
      },
      {
        "code": "REQUIRED_NOT_BLANK",
        "property": "name",
        "message": "must not be blank",
        "rejectedValue": null
      }
    ]
  }
  
  

• Returning the fully qualified name of the exception that is thrown,which can be used by machines to react to the error, as well as a human readable message with detailed info

  {
    "code": "com.wimdeblauwe.examples.errorhandling.inforequest.InfoRequestNotFoundException",
    "message": "There is no known info request with id 1"
  }
  

Those aside you can also customize the error code, add extra fields to the error response, and log exceptions through the error.handling.exception-logging property.

As of this month, release 1.6.0 adds a few extras:

• New default error code generation strategy, embracing the ALL_CAPS error code style.

That is,before 1.6.0 you were getting

"code": "com.company.application.user.UserNotFoundException",

now you get

"code": "USER_NOT_FOUND", 

• Returning the HTTP response status in response body: 

{
  "status": 404, 
  "code": "USER_NOT_FOUND",
  "message": "Could not find user with id 123"
} 

• More support for validation problems.Two new features have been added to support error response related to validation:

The javax.validation.ConstraintViolationException is now  supported. This exception is used when you validate on a Service method for example, as opposed to validating the RequestBody in the Controller.

Validation annotations on a @RequestParam parameter now leads to the addition of parameterErrors in the error response. 

• New documentation website at:
  https://wimdeblauwe.github.io/error-handling-spring-boot-starter/    

In summary, to improve on the Spring boot defaults and enjoy a better and standardized error handling, go the easy way and just include in your project the Error Handling Spring Boot Starter dependency through Maven or Gradle.

More Information

Error Handling Spring Boot Starter release 1.6.0

Error Handling Spring Boot Starter Github

Error Handling Spring Boot Starter documentation

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