Spring Boot human readable error messages after JSON parsing error

Question

I have a REST API written using Spring Boot. Now I would like to to enhance error handling. If user sends either not valid JSON or JSON which can not me deserialized to my DTO I would to inform user what exactly was wrong, eg unexpected property name, type etc. Still I don't want to expose any information about the implementation (eg stacktrace, class names).

Default Spring implementation returns

InvalidFormatException: Cannot deserialize value of type `java.lang.Integer` from String \"aaa\": not a valid Integer value\n at [Source: (PushbackInputStream); line: 10, column: 19]
 (through reference chain: com.yell.statementofwork.model.StatementOfWorkCompletionDtoSe[\"purchasedProducts\"]->java.util.ArrayList[0]->com.yell.statementofwork.model.PurchasedProductDtoSe[\"quantity\"])",

which is almost good but I would prefer to remove information about class from it. Do you have any proposition how to do that?

Answer 1

you can create your own custom ConstraintValidator and annotate your DTO object with corresponding annotation

you can find the example here - http://dolszewski.com/spring/custom-validation-annotation-in-spring/

PS the example is using annotation for one field, but you can use it on the whole class

Answer 2

The cleanest way to handle different types of errors in a spring boot REST API is by using spring AOP. First, let's create a custom Exception class

public class InvalidFormatException extends RuntimeException {

    private final String message;
    private final List<String> data;

    // getters , setters and constructors
}

Then create an error response model class. This model class will provide a JSON structure of what should sent back to the user in case of an exception

public class ErrorResponseModel {
    
    String code;
    String type;
    String message;
    List<String> data;

    // getters, setters, and constructor
}

Then create a custom exception handler for your controller using spring AOP

@ControllerAdvice
public class ControllerExceptionHandler {

    @ExceptionHandler(InvalidFormatException.class)
    public ResponseEntity<ErrorResponseModel> badRequestException(InvalidFormatException ex, WebRequest request) {
        return new ResponseEntity<>(new ErrorResponseModel(ex.getMessage(), ex.getData()),
                HttpStatus.BAD_REQUEST);
    }
}

You can add and handle more error types like this in this class. Now whenever you throw an Exception, it will be intercepted here and a custom error response will be sent back to the user.