Modify default JSON error response from Spring Boot Rest Controller

If there is empty message text in json when you encounter exception, you can be hit by changed behavior in spring boot 2.3.0. If this is the case, just change your server.error.include-message property to always.

Following answer is totally derived from Andy Wilkinson's answer (which uses web.reactive classes)
- It includes web.servlet based classes.
- Spring boot 2.2.4.RELEASE

ExceptionHandlerConfig.java

package com.example.sample.core.exception;

import java.util.LinkedHashMap;
import java.util.Map;

import org.springframework.boot.web.servlet.error.DefaultErrorAttributes;
import org.springframework.boot.web.servlet.error.ErrorAttributes;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.context.request.WebRequest;

@Configuration
public class ExceptionHandlerConfig {

    //private static final String DEFAULT_KEY_TIMESTAMP = "timestamp";
    private static final String DEFAULT_KEY_STATUS = "status";
    private static final String DEFAULT_KEY_ERROR = "error";
    private static final String DEFAULT_KEY_ERRORS = "errors";
    private static final String DEFAULT_KEY_MESSAGE = "message";
    //private static final String DEFAULT_KEY_PATH = "path";

    public static final String KEY_STATUS = "status";
    public static final String KEY_ERROR = "error";
    public static final String KEY_MESSAGE = "message";
    public static final String KEY_TIMESTAMP = "timestamp";
    public static final String KEY_ERRORS = "errors";

    //

    @Bean
    public ErrorAttributes errorAttributes() {
        return new DefaultErrorAttributes() {

            @Override
            public Map<String ,Object> getErrorAttributes(
                WebRequest webRequest
                ,boolean includeStackTrace
            ) {
                Map<String ,Object> defaultMap
                    = super.getErrorAttributes( webRequest ,includeStackTrace );

                Map<String ,Object> errorAttributes = new LinkedHashMap<>();
                // Customize.
                // For eg: Only add the keys you want.
                errorAttributes.put( KEY_STATUS, defaultMap.get( DEFAULT_KEY_STATUS ) );                    
                errorAttributes.put( KEY_MESSAGE ,defaultMap.get( DEFAULT_KEY_MESSAGE ) );

                return errorAttributes;
            }
        };
    }
}

As described in the documentation on error handling, you can provide your own bean that implements ErrorAttributes to take control of the content.

An easy way to do that is to subclass DefaultErrorAttributes. For example:

@Bean
public ErrorAttributes errorAttributes() {
    return new DefaultErrorAttributes() {
        @Override
        public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes, boolean includeStackTrace) {
            Map<String, Object> errorAttributes = super.getErrorAttributes(requestAttributes, includeStackTrace);
            // Customize the default entries in errorAttributes to suit your needs
            return errorAttributes;
        }

   };
}