Does having a custom error response mean that you have to catch any exception in order to be consistent? - spring

Question

In my spring boot project i have a User class and its' fields have annotation constrains like #Size, #Pattern #NotNull etc.
For example
#Id
#Column(name = "name", nullable = false, length = 16, unique = true)
#NotNull
#Size(max = 16, message = "Username should be less or equal than 16 characters")
#Pattern(regexp = "[^\s]*", message = "Username should not contain whitespaces")
#Pattern(regexp = "^[A-Za-zΑ-Ωα-ωΆ-Ώά-ώ].*$", message = "Username should should start with a letter")
private String userName;
A post request with invalid userName returns the following error response
{
"timestamp":"2021-06-28T18:02:02.720+00:00",
"status":400,
"error":"Bad Request",
"message":"Validation failed for object='user'. Error count: 1",
"errors":[
{
"codes":[
"Pattern.user.userName",
"Pattern.userName",
"Pattern.java.lang.String",
"Pattern"
],
"arguments":[
{
"codes":[
"user.userName",
"userName"
],
"arguments":null,
"defaultMessage":"userName",
"code":"userName"
},
[
],
{
"defaultMessage":"^[A-Za-zΑ-Ωα-ωΆ-Ώά-ώ].*$",
"arguments":null,
"codes":[
"^[A-Za-zΑ-Ωα-ωΆ-Ώά-ώ].*$"
]
}
],
"defaultMessage":"Username should should start with a letter",
"objectName":"user",
"field":"userName",
"rejectedValue":"5",
"bindingFailure":false,
"code":"Pattern"
}
],
"path":"/signup"
}
Before questioning if this kind of error format is what i need, i didn't like it so i tried to make my own like in this guide Baeldung
I have a global controller now to deal with custom errors like when the username is taken.
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {...}
This is what i get now
{
"timestamp": "29-06-2021 05:05:03",
"status": "BAD_REQUEST",
"message": "Invalid input",
"path": "/signup",
"errors": [
{
"field": "userName",
"message": "Username should should start with a letter",
"rejectedValue": "5"
}
]
}
I suppose a good API means that you have to be consistent, that is we always have to return an error response with the same structure.
I have override some ResponseEntityExceptionHandler's method in order to catch other errors but there are still many methods to override. Here is a list of the remaining methods.
// handleBindException
// handleTypeMismatch
// handleMissingServletRequestPart
// handleMissingServletRequestParameter
// handleMethodArgumentTypeMismatch
// handleConstraintViolation
// handleHttpMediaTypeNotAcceptable
// handleMissingPathVariable
// handleServletRequestBindingException
// handleConversionNotSupported
// handleHttpMessageNotWritable
// handleAsyncRequestTimeoutException
My questions:
Do i have to catch all these exceptions? To be more specific, is it always possible to take all these exceptions no matter how your domains, controllers, services work?
Can you please write for each of these exceptions a bad request that will cause them to be thrown? Please, don't just tell me when they will be thrown. I'm new to spring and i won't be able to understand without an example.

Answer 1

How about overriding the below method from ResponseEntityExceptionHandler, as it is being invoked by all methods mentioned in the query.
protected ResponseEntity<Object> handleExceptionInternal()
And have your own logic to check the instance of exception and provide different kind of error response to client.