Develop Reference

What's the best option/alternative to treat exceptions in spring boot?

Right now i'm using this example of exception handling:
//get an object of type curse by id
//in the service file, this findCurseById() method throws a
//CursaNotFoundException
#GetMapping("/{id}")
public ResponseEntity<curse> getCursaById (#PathVariable("id") Long id) {
curse c = curseService.findCurseById(id);
return new ResponseEntity<>(c, HttpStatus.OK);
}
//so if not found, this will return the message of the error
#ResponseStatus(HttpStatus.NOT_FOUND)
#ExceptionHandler(CursaNotFoundException.class)
public String noCursaFound(CursaNotFoundException ex) {
return ex.getMessage();
}
and that's my exception
public class CursaNotFoundException extends RuntimeException {
public CursaNotFoundException(String s) {
super(s);
}
}
in future I want to use Angular as front-end, so I don't really know how I should treat the exceptions in the back-end. For this example let's say, should I redirect the page to a template.html page in the noCursaFound() method, or should I return something else? A json or something? I couldn't find anything helpful. Thanks

I would suggest keeping the error handling at the REST API level and not redirecting to another HTML page on the server side. Angular client application consumes the API response and redirects to template.html if needed.
Also, it would be better if the backend returns an ApiError when an exception occurs with a message and, optionally, an error code:
public class ApiError {
private String message;
private String code;
}
and handle the exceptions in a separate class, ExceptionHandler annotated with #ControllerAdvice:
#ControllerAdvice
public class ExceptionHandler {
#ExceptionHandler(value = CursaNotFoundException.class)
public ResponseEntity cursaNotFoundException(CursaNotFoundException cursaNotFoundException) {
ApiError error = new ApiError();
error.setMessase(cursaNotFoundException.getMessage());
error.setCode(cursaNotFoundException.getCode());
return new ResponseEntity(error, HttpStatus.NOT_FOUND);
}
#ExceptionHandler(value = Exception.class)
public ResponseEntity<> genericException(Exception exception) {
ApiError error = new ApiError();
error.setMessase(exception.getMessage());
error.setCode("GENERIC_ERROR");
return new ResponseEntity<>(error, HttpStatus.INTERNAL_SERVER_ERROR);
}
}

Can Spring controller produce multiple content types combinations using same endpoint?

I need to serve multiple file types using same endpoint ( zip,pdf,xml).
I needed to add error handling to those endpoints so in case of error they should return json (using controller advice) to indicate problem to user.
For example:
#GetMapping(value = "api/books", produces = {applicaton/zip, application/json}
public ResponseEntity<byte[]> getZipedBooks(){...}
#GetMapping(value = "api/books", produces = {applicaton/pdf, application/json}
public ResponseEntity<byte[]> getPdfBooks()(...}
Without application/json Spring was able to differentiate between those endpoints and call correct one based on accept header. But when I added json Spring is now throwing exception:
org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
even if it can be deduced from accept: application/json,application/pdf header that getPdfBooks should be called.
Is there any way to configure spring to work with multiple content types on the same endpoint or I need to make special endpoints for every file type ?

I would reconsider this approach. If you want to return JSON on error do with exception handling
So that you would add something like
private class ErrorResponse {
String message;
public ErrorResponse(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
#ExceptionHandler(value = Exception.class)
public ResponseEntity<ErrorResponse> handleException(Exception e) {
return new ResponseEntity<ErrorResponse>(new ErrorResponse(e.getMessage()), HttpStatus.BAD_REQUEST);
}

Spring REST add field to 404 resonse code

Using latest Spring Boot as of May 2018. I've created a 404 response like this.
#ResponseStatus(HttpStatus.NOT_FOUND)
public class NotFoundException extends RuntimeException {
private final int errorId;
public NotFoundException(String errorMsg) {
super("-1," + errorMsg);
this.errorId = -1;
}
public NotFoundException(int errorId, String errorMsg) {
super(errorId + "," + errorMsg);
this.errorId = errorId;
}
public int getErrorId() {
return errorId;
}
}
The annotation #ResponseStatus(HttpStatus.NOT_FOUND) makes my NotFoundException appear like a 404 reponse like this
{
"timestamp":1527751944754,
"status":404,
"error":"Not Found",
"exception":"com.myapp.exception.NotFoundException",
"message":"1000,Could not find data for owner: 1234","path":"/resource/owner/1234"
}
I hoped that property "getErrorId" would appear in the response automatically, like this
{
"timestamp":1527751944754,
"status":404,
"error":"Not Found",
"exception":"com.myapp.exception.NotFoundException",
"message":"Could not find data for owner: 1234","path":"/resource/owner/1234",
"errorId": 1000
}
Is the a simply way (like an annotiation to the getErrorId method) of having the property "errorId" in the response?

You use #ControllerAdvice and #ExceptionHanlder in Spring. that is exception controller. In fact, you will make custom exception controller and define exception.
This is sample code for you :
#ControllerAdvice("your.package")
public class CommonExceptionHandler {
#ExceptionHandler(value = NoHandlerFoundException.class)
#ResponseStatus(value = HttpStatus.NOT_FOUND)
public #ResponseBody ResponseEntity<?> setNotFoundException(Exception exception) throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
// this is sample map. you will make your custom model and you use exception parameter.
Map<String, String> map = new HashMap<String, String>();
map.put("timestamp", String.valueOf(new Date().getTime()));
map.put("status", HttpStatus.NOT_FOUND.toString());
map.put("error", "Not Found");
map.put("exception", exception.getMessage());
map.put("message", "Could not find data for owner: 1234");
map.put("path", "/resource/owner/1234");
map.put("errorId", "1000");
String json = mapper.writeValueAsString(map);
return ResponseEntity.status(HttpStatus.NOT_FOUND).body(json);
}
}

what ever Byeon0gam told everything is fine, here i am going to show another way means little bit of difference in maintaining code.
We know already ,
we can handle exceptions in spring-rest by 4 ways:
1. Using ResponseEntity Class.
2. Using #ResponseStatus Annotation.
3. Using #ExceptionHandler() Annotation.
4. Return Error Representation instead of default HTML error Page.
By using Those we can handle Exceptions at Method or Class level only.
But, if you want to handle Globally means throughout application , please follow below steps.
Handling Global Exception:
To Handle all Exceptions in our applications ,
First we need to create a class, after we need to use #ControllerAdvice Annotation on top of a class. In that class body , we can handle the exceptions raised in our application.
In that Class , we will create Exception handling methods , on top of every method we will use #ExceptionHandler() annotation for navigating Exceptions and for Handling .
If any exception raises in our application , based on #ExceptionHandler(“argument”) annotation argument the exception hadling method will be invoked and remaining handling code will be excuted.
#ControllerAdvice
public class SpringRestGlobalExceptionHandler {
#ExceptionHandler(Exception.class)
public ResponseEntity<?> exceptionHandler(HttpServletRequest req, Exception e)
{
JSONObject obj =new JSONObject();
obj.put("msgTxt","Unknown Server Error, Please Contact Admin." );
obj.put("reqUrl", req.getRequestURI());
obj.put("stackTrace", e.toString());
obj.put("isErrorFlag", true);
obj.put("httpStatusCode", HttpStatus.OK.value());
gstcDaoi.saveExceptionOrErrorLog(prepareTGstcExceptionOrErrorLogObject(obj));
e.printStackTrace();
return new ResponseEntity<>(obj, HttpStatus.OK);
}

Netflix Feign - Propagate Status and Exception through Microservices

I'm using Netflix Feign to call to one operation of a Microservice A to other other operation of a Microservice B which validates a code using Spring Boot.
The operation of Microservice B throws an exception in case of the validation has been bad. Then I handled in the Microservices and return a HttpStatus.UNPROCESSABLE_ENTITY (422) like next:
#ExceptionHandler({
ValidateException.class
})
#ResponseStatus(HttpStatus.UNPROCESSABLE_ENTITY)
#ResponseBody
public Object validationException(final HttpServletRequest request, final validateException exception) {
log.error(exception.getMessage(), exception);
error.setErrorMessage(exception.getMessage());
error.setErrorCode(exception.getCode().toString());
return error;
}
So, when Microservice A calls to B in a interface as next:
#Headers("Content-Type: " + MediaType.APPLICATION_JSON_UTF8_VALUE)
#RequestLine("GET /other")
void otherOperation(#Param("other") String other );
#Headers("Content-Type: " + MediaType.APPLICATION_JSON_UTF8_VALUE)
#RequestLine("GET /code/validate")
Boolean validate(#Param("prefix") String prefix);
static PromotionClient connect() {
return Feign.builder()
.encoder(new GsonEncoder())
.decoder(new GsonDecoder())
.target(PromotionClient.class, Urls.SERVICE_URL.toString());
}
and the validations fails it returns a internal error 500 with next message:
{
"timestamp": "2016-08-05T09:17:49.939+0000",
"status": 500,
"error": "Internal Server Error",
"exception": "feign.FeignException",
"message": "status 422 reading Client#validate(String); content:\n{\r\n \"errorCode\" : \"VALIDATION_EXISTS\",\r\n \"errorMessage\" : \"Code already exists.\"\r\n}",
"path": "/code/validate"
}
But I need to return the same as the Microservice operation B.
Which would be the best ways or techniques to propagate Status and Exceptions through microservices using Netflix Feign?

You could use a feign ErrorDecoder
https://github.com/OpenFeign/feign/wiki/Custom-error-handling
Here is an example
public class MyErrorDecoder implements ErrorDecoder {
private final ErrorDecoder defaultErrorDecoder = new Default();
#Override
public Exception decode(String methodKey, Response response) {
if (response.status() >= 400 && response.status() <= 499) {
return new MyBadRequestException();
}
return defaultErrorDecoder.decode(methodKey, response);
}
}
For spring to pick up the ErrorDecoder you have to put it on the ApplicationContext:
#Bean
public MyErrorDecoder myErrorDecoder() {
return new MyErrorDecoder();
}

Shameless plug for a little library I did that uses reflection to dynamically rethrow checked exceptions (and unchecked if they are on the Feign interface) based on an error code returned in the body of the response.
More information on the readme :
https://github.com/coveo/feign-error-decoder

OpenFeign's FeignException doesn't bind to a specific HTTP status (i.e. doesn't use Spring's #ResponseStatus annotation), which makes Spring default to 500 whenever faced with a FeignException. That's okay because a FeignException can have numerous causes that can't be related to a particular HTTP status.
However you can change the way that Spring handles FeignExceptions. Simply define an ExceptionHandler that handles the FeignException the way you need it (see here):
#RestControllerAdvice
public class GlobalExceptionHandler {
#ExceptionHandler(FeignException.class)
public String handleFeignStatusException(FeignException e, HttpServletResponse response) {
response.setStatus(e.status());
return "feignError";
}
}
This example makes Spring return the same HTTP status that you received from Microservice B. You can go further and also return the original response body:
response.getOutputStream().write(e.content());

Write your custom exception mapper and register it. You can customize responses.
Complete example is here
public class GenericExceptionMapper implements ExceptionMapper<Throwable> {
#Override
public Response toResponse(Throwable ex) {
return Response.status(500).entity(YOUR_RETURN_OBJ_HERE).build();
}
}

Since 2017 we've created a library that does this from annotations (making it fairly easy to, just like for requests/etc, to code this up by annotations).
it basically allows you to code error handling as follows:
#ErrorHandling(codeSpecific =
{
#ErrorCodes( codes = {401}, generate = UnAuthorizedException.class),
#ErrorCodes( codes = {403}, generate = ForbiddenException.class),
#ErrorCodes( codes = {404}, generate = UnknownItemException.class),
},
defaultException = ClassLevelDefaultException.class
)
interface GitHub {
#ErrorHandling(codeSpecific =
{
#ErrorCodes( codes = {404}, generate = NonExistentRepoException.class),
#ErrorCodes( codes = {502, 503, 504}, generate = RetryAfterCertainTimeException.class),
},
defaultException = FailedToGetContributorsException.class
)
#RequestLine("GET /repos/{owner}/{repo}/contributors")
List<Contributor> contributors(#Param("owner") String owner, #Param("repo") String repo);
}
You can find it in the OpenFeign organisation:
https://github.com/OpenFeign/feign-annotation-error-decoder
disclaimer: I'm a contributor to feign and the main dev for that error decoder.

What we do is as follows:
Share common jar which contains exceptions with both microservices.
1.) In microservices A convert exception to a DTO class lets say ErrorInfo.
Which will contain all the attributes of your custom exception with a String exceptionType, which will contain exception class name.
2.) When it is received at microservice B it will be handled by ErrorDecoder in microservice B and It will try to create an exception object from exceptionType as below:
#Override
public Exception decode(String methodKey, Response response) {
ErrorInfo errorInfo = objectMapper.readValue(details, ErrorInfo.class);
Class exceptionClass;
Exception decodedException;
try {
exceptionClass = Class.forName(errorInfo.getExceptionType());
decodedException = (Exception) exceptionClass.newInstance();
return decodedException;
}
catch (ClassNotFoundException e) {
return new PlatformExecutionException(details, errorInfo);
}
return defaultErrorDecoder.decode(methodKey, response);
}

How should behave rest controller when during a processing occur a error

I have question that interest me.
Assume that I have some rest controller and some rest client writing in javascript. This client send request to a controller and during a processing occur some error. How should behave controller in this situation? Should return null? or string with message?
For example, We have controller like this:
#RequestMapping("/user", method = RequestMethod.POST)
public #ResponseBody String createUser(User user) {
try {
userService.create(user);
} catch(UserCreationException e) {
}
}
This is very simple example but is many different examples of controllers like controller which return some resources or only change state on the server side and I don't know what to do when occur error.

in improving developer(your consumers) experience , it is a good idea to respond with appropriate error messages on the response body in addition to the Http status code.
Here is an example with spring, mainly throw an exception that you can deal with by extending ResponseEntityExceptionHandler #ControllerAdvice
#ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException{
private static final long serialVersionUID = 1L;
public ResourceNotFoundException(String message) {
super(message);
}
}
#Controller
#RequestMapping("/XXXXXs")
public class DoctypesController {
#RequestMapping( method = RequestMethod.GET , value="/xxx")
public ResponseEntity<?> getXXXXXX(HttpServletRequest request) {
if (XXX == null ) {
throw new ResourceNotFoundException("XXXX Not found for);
}else{
response = buildResponse(xxxx)
}
return response;
}
}
#ControllerAdvice
public class XXXXEntityExceptionHandler extends ResponseEntityExceptionHandler {
#ExceptionHandler(value = { ResourceNotFoundException.class })
protected ResponseEntity<Object> handleMissingResource(RuntimeException ex, final WebRequest request) {
HttpStatus status = HttpStatus.NOT_FOUND;
return new ResponseEntity<Object>(new Error(String.valueOf(status.value()), status.getReasonPhrase(),ex.getMessage()),status);
}
}

According http specifications, the server must return a error code >= 500 in case of internal error during processing.
If the error is caused because the client did a wrong request : the server must return a error code >= 400 and < 500
Of course, on client side you must take care to handle those errors properly (i.e. displaying a friendly error message or something like that).

You should really use the HTTP Error codes and handle the HTTP error codes using your client-side technology, ie. JavaScript in your case.
For example: given a user who is unauthorised to read/access a Resource, then the 403 error code should be returned to the client. By using the standard HTTP/REST Error codes, you conform to an API that can be understood by any client, whether JavaScript or something else.
With Spring MVC and Rest controllers, it's really easy. Create a simple class for your Exception and annotate the class with the HTTP Error code, e.g. #ResponseStatus(value = HttpStatus.FORBIDDEN) for a 403 error. Then in your Controller, you can throw the exception which would in turn return the HTTP error code.