We Keep Coding

How to pass API exception output to through own REST service?

Summary :
I want to pass valid exception output given by one REST service end point to the end user by using my own Rest service.
What I did is, I have called that service in service class using RestTemplate class, it's giving valid output on valid post request. But when I am passing invalid input to it I am getting only '400 BAD REQUEST' result in my service class where I have called that API. But when I am calling that API separately using postman, there I'm getting expected output.
Code sample :
class Abc {
ResponseEntity<String> = response;
static final String url = "https://abc-xyz.com/client-rest-end-point-url";
public ResponseEntity getDetails(RequestInput requestInput) {
try{
response=restTemplate.postForObject(url,requestInput,String.class);
} catch(Exception e) {
ResponseEntity response = (ResponseEntity<ErrorModel>)restTemplate.postForEntity(url,requestInput,ErrorModel.class);
}//try-catch
}//getDetails method
}//class

You can create a custom exception class for your entire application and you can send data in JSON by using throw keyword
Suppose you have exception class is:
public class TestException extends Exception {
private static final long serialVersionUID = 1L;
private String code;
private String detailMessage;
public TestException() {
};
public TestException(String message, String code, String detailMessage) {
super(message);
this.code = code;
this.detailMessage = detailMessage;
}
public TestException(String message, String code) {
super(message);
this.code = code;
}
//TestExceptionResponseCode is another class for message data, if required.
public TestException(TestExceptionResponseCode testExceptionResponseCode) {
super(testExceptionResponseCode.getMessage());
this.code = testExceptionResponseCode.getCode();
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public String getDetailMessage() {
return detailMessage;
}
public void setDetailMessage(String detailMessage) {
this.detailMessage = detailMessage;
}
}
Now in your case throwing exception can be like :
class Abc {
ResponseEntity<String> = response;
static final String url = "https://abc-xyz.com/client-rest-end-point-url";
public ResponseEntity getDetails(RequestInput requestInput) {
if(requestInput==null){
throw new TestException("FAILED", "1", "Data can't be null");
}
}

Annotate your method with #ExceptionHandler annotation. You can code in seperate class from controller.
#ControllerAdvice
public class YourExceptionHandler {
#ExceptionHandler(CustomException.class)
public String xException() {
return "error/exception";
}
}

Checking business logic in controller to provide better error messages

I have a service method that returns a UserDto object. However there are several situations where the request to the controller would return a HTTP status other than 200 but the service can only return null or the UserDto.
Is it bad practice to move some of the business logic to the controller and call the repository directly in order to return more detailed error messages, since the service cannot pass back an error message to the contoller?

You can do a bit better by having the service throw business exception, and the controller react on that. For example, a CustomerService could throw a `CustomerNotFoundException', and the controller could turn that into an appropriate HTTP status code, like this:
#ExceptionHandler({ CustomerNotFoundException.class })
public ResponseEntity handleException(CustomerNotFoundException ex, WebRequest request) {
ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), request.getDescription(false));
return new ResponseEntity<>(errorDetails, HttpStatus.NOT_FOUND);
}
I recommend against moving the business logic to the controller, since the controller is more of an infrastructure component than domain logic. Also, consider adding another protocol, for example, a binary protocol, which wouldn't use the controller layer. You might miss your validations or business rules.

You can also use #ControllerAdvice from Spring to handle such cases, take a look at the below code.I hope this should help you return detailed error messages to the the controller.
#Order(Ordered.HIGHEST_PRECEDENCE)
#ControllerAdvice
public class ApiExceptionHandler extends ResponseEntityExceptionHandler {
#ExceptionHandler(NoSuchUserException.class)
public ResponseEntity<Object> handleNoSuchPinCodeException(
NoSuchUserException ex) {
ApiError apiError = new ApiError(HttpStatus.NOT_FOUND);
apiError.setErrorMessage(ex.getMessage());
return buildResponseEntity(apiError);
}
private ResponseEntity<Object> buildResponseEntity(ApiError apiError) {
return new ResponseEntity<>(apiError, apiError.getStatus());
}
}
public class NoSuchUserException extends Exception{
public NoSuchUserException (String message) {
super(message);
}
}
public class ApiError {
private HttpStatus status;
private String errorMessage;
private ApiError() {
}
public ApiError(HttpStatus status) {
this();
this.status = status;
}
public ApiError(HttpStatus status, String errorMessage, Throwable ex) {
this();
this.status = status;
this.errorMessage = errorMessage;
}
public HttpStatus getStatus() {
return status;
}
public void setStatus(HttpStatus status) {
this.status = status;
}
public String getErrorMessage() {
return errorMessage;
}
public void setErrorMessage(String errorMessage) {
this.errorMessage = errorMessage;
}
}

#RequestBody #Valid SomeDTO has field of enum type, custom error message

I have the following #RestController
#RequestMapping(...)
public ResponseEntity(#RequestBody #Valid SomeDTO, BindingResult errors) {
//do something with errors if validation error occur
}
public class SomeDTO {
public SomeEnum someEnum;
}
If the JSON request is { "someEnum": "valid value" }, everything works fine. However, if the request is { "someEnum": "invalid value" }, it only return error code 400.
How can I trap this error so I can provide a custom error message, such as "someEnum must be of value A/B/C".

The answer provided by #Amit is good and works. You can go ahead with that if you want to deserialize an enum in a specific way. But that solution is not scalable. Because every enum which needs validation must be annotated with #JsonCreator.
Other answers won't help you beautify the error message.
So here's my solution generic to all the enums in spring web environment.
#RestControllerAdvice
public class ControllerErrorHandler extends ResponseEntityExceptionHandler {
public static final String BAD_REQUEST = "BAD_REQUEST";
#Override
public ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException exception,
HttpHeaders headers, HttpStatus status, WebRequest request) {
String genericMessage = "Unacceptable JSON " + exception.getMessage();
String errorDetails = genericMessage;
if (exception.getCause() instanceof InvalidFormatException) {
InvalidFormatException ifx = (InvalidFormatException) exception.getCause();
if (ifx.getTargetType()!=null && ifx.getTargetType().isEnum()) {
errorDetails = String.format("Invalid enum value: '%s' for the field: '%s'. The value must be one of: %s.",
ifx.getValue(), ifx.getPath().get(ifx.getPath().size()-1).getFieldName(), Arrays.toString(ifx.getTargetType().getEnumConstants()));
}
}
ErrorResponse errorResponse = new ErrorResponse();
errorResponse.setTitle(BAD_REQUEST);
errorResponse.setDetail(errorDetails);
return handleExceptionInternal(exception, errorResponse, headers, HttpStatus.BAD_REQUEST, request);
}
}
This will handle all the invalid enum values of all types and provides a better error message for the end user.
Sample output:
{
"title": "BAD_REQUEST",
"detail": "Invalid enum value: 'INTERNET_BANKING' for the field: 'paymentType'. The value must be one of: [DEBIT, CREDIT]."
}

#ControllerAdvice
public static class GenericExceptionHandlers extends ResponseEntityExceptionHandler {
#Override
protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException e, HttpHeaders headers, HttpStatus status, WebRequest request) {
return new ResponseEntity<>(new ErrorDTO().setError(e.getMessage()), HttpStatus.BAD_REQUEST);
}
}
I created a fully functional Spring boot Application with a Test on Bitbucket

You do not need #Valid for enum validation, you can achieve the required response using below code:
Controller Code, StackDTO has an enum PaymentType in it:
#RequestMapping(value = "/reviews", method = RequestMethod.POST)
#ResponseBody
public ResponseEntity<String> add(#RequestBody StackDTO review) {
return new ResponseEntity<String>(HttpStatus.ACCEPTED);
}
Create an exception class, as EnumValidationException
public class EnumValidationException extends Exception {
private String enumValue = null;
private String enumName = null;
public String getEnumValue() {
return enumValue;
}
public void setEnumValue(String enumValue) {
this.enumValue = enumValue;
}
public String getEnumName() {
return enumName;
}
public void setEnumName(String enumName) {
this.enumName = enumName;
}
public EnumValidationException(String enumValue, String enumName) {
super(enumValue);
this.enumValue = enumValue;
this.enumName = enumName;
}
public EnumValidationException(String enumValue, String enumName, Throwable cause) {
super(enumValue, cause);
this.enumValue = enumValue;
this.enumName = enumName;
}
}
I have enum as below, with a special annotation #JsonCreator on a method create
public enum PaymentType {
CREDIT("Credit"), DEBIT("Debit");
private final String type;
PaymentType(String type) {
this.type = type;
}
String getType() {
return type;
}
#Override
public String toString() {
return type;
}
#JsonCreator
public static PaymentType create (String value) throws EnumValidationException {
if(value == null) {
throw new EnumValidationException(value, "PaymentType");
}
for(PaymentType v : values()) {
if(value.equals(v.getType())) {
return v;
}
}
throw new EnumValidationException(value, "PaymentType");
}
}
Finally RestErrorHandler class,
#ControllerAdvice
public class RestErrorHandler {
#ExceptionHandler(HttpMessageNotReadableException.class)
#ResponseStatus(HttpStatus.BAD_REQUEST)
#ResponseBody
public ResponseEntity<ValidationErrorDTO> processValidationIllegalError(HttpMessageNotReadableException ex,
HandlerMethod handlerMethod, WebRequest webRequest) {
EnumValidationException exception = (EnumValidationException) ex.getMostSpecificCause();
ValidationErrorDTO errorDTO = new ValidationErrorDTO();
errorDTO.setEnumName(exception.getEnumName());
errorDTO.setEnumValue(exception.getEnumValue());
errorDTO.setErrorMessage(exception.getEnumValue() + " is an invalid " + exception.getEnumName());
return new ResponseEntity<ValidationErrorDTO>(errorDTO, HttpStatus.BAD_REQUEST);
}
}
ValidationErrorDTO is the dto with setters/getters of enumValue, enumName and errorMessage. Now when you send POST call to controller endpoint /reviews with below request
{"paymentType":"Credit2"}
Then code returns response as 400 with below response body -
{
"enumValue": "Credit2",
"enumName": "PaymentType",
"errorMessage": "Credit2 is an invalid PaymentType"
}
Let me know if it resolves your issue.

Yon can achieve this using #ControllerAdvice as follows
#org.springframework.web.bind.annotation.ExceptionHandler(value = {InvalidFormatException.class})
public ResponseEntity handleIllegalArgumentException(InvalidFormatException exception) {
return ResponseEntity.badRequest().body(exception.getMessage());
}
Basically , the idea is to catch com.fasterxml.jackson.databind.exc.InvalidFormatException and handle it as per your requirement.

#Valid has to do with Hibernate bean validation. Currently enum type is not supported out of the box. I found this answer to be the closet, https://funofprograming.wordpress.com/2016/09/29/java-enum-validator/, the drawback however is that you have to make the enum field of type String instead.

Restlet error response format in JSON

Im using the restlet framework to manager a projects API. It seems that by default error responses are formatted in HTML. How can I change that so that by default ALL error responses are in JSON format?
I've tried adding a custom converter which works great for the entity responses but not for error responses.
We have 110+ endpoints that support application/json so ideally I would like to just set the default errors to always return as JSON. The default converter works for all methods that return an actual entity.
#Get("json")
#Produces("application/json")
public User represent() {
...
return result;
}
But the ResourceException thrown by this method returns HTML.

If you are sure about the format your service is going to produce then you can annotate your service class with #Produces annotation at class level. Then you will not be required to define the same for each and every method.
Also, once #Produces is defined at class level and you want to change response format for a particular method then you can annotate that particular method for other format.
Try Below code..
public Response represent(){
try{
}catch(Exception ex){
return Response.status(500)
.entity(new ExceptionMessage("500", ex.getMessage()))
.type(MediaType.APPLICATION_JSON).
build();
}
return Response.status(Response.Status.OK).entity(result).build();
}
And have below Model class for exception message.
#XmlRootElement
class ExceptionMessage{
private String statusCode;
private String errorMessage;
public ExceptionMessage() {
}
public ExceptionMessage(String statusCode, String errorMessage) {
this.statusCode = statusCode;
this.errorMessage = errorMessage;
}
public String getErrorMessage() {
return errorMessage;
}
public void setErrorMessage(String errorMessage) {
this.errorMessage = errorMessage;
}
public String getStatusCode() {
return statusCode;
}
public void setStatusCode(String statusCode) {
this.statusCode = statusCode;
}
}
This is the link dedicated to Restlet.

SpringMVC: ExceptionHandler fails to catch my custom exception

In my main controller, when the exception is thrown, I want it to be catched by the ExceptionHandler in my error handling controller, but that never happens. Instead, I am getting Error 500. I am suspecting the problem is in #ResponseBody annotation of my main controller. Any idea how to achieve wanted behavior?
Main controller
#RequestMapping(value = "/person/{person}", method = RequestMethod.GET)
public #ResponseBody Person execute(#PathVariable(value = "person") String person) {
if(person.isValid(person)) {
return person;
} else {
throw new ResourceNotFoundException("Invalid person format.");
}
}
Exception
#ResponseStatus(value = HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
public ResourceNotFoundException() {
}
public ResourceNotFoundException(String message) {
super(message);
}
public ResourceNotFoundException(String message, Throwable throwable) {
super(message, throwable);
}
public ResourceNotFoundException(Throwable throwable) {
super(throwable);
}
}
Error controller
private static final String ERROR_PAGE = "errors/error.jsp";
#ResponseStatus(value = HttpStatus.NOT_FOUND)
#ExceptionHandler(ResourceNotFoundException.class)
public ModelAndView invalidApiCall(){
return generateView(ERROR_404);
}
private ModelAndView generateView(String errorCode) {
return new ModelAndView(ERROR_PAGE);
}
My error view never gets generated (#ExceptionHandler never catches the exception). Instead I am getting error 500. Is there a way for ExceptionHandler to catch my exception?

Try to add #ControllerAdvice annotation for the Error Controller. If it is already added, check whether the class' package is included in package scan.