I recently started learning annotations and I want to know can a method annotation handle errors thrown by this method? Or to know the code of this exception/error.
P.S. if it can, next step is to retry this method in dependence of error code
P.S.S. I know about spring Retryable, but i can't use it. I tried to find info about my question in the google, but i didn't find.
Annotation on its own does nothing. It is just to mark code. You need to have some handlers, that scan your classes and react in case of annotation.
Most frameworks already have handlers and scanners, so developer include proper framework, add proper annotations, and thanks to that frameworks will perform some work for developer or application.
btw, for error handling, I recommend using a simple proxy like this:
Invoke method in another class's try catch block
You are probably more thinking about Aspect Oriented Programming.
Meaning: java annotations aren't about adding functionality "into" methods. They are markers that are "evaluated" by some sort of component (either the compiler at compile time, or some framework at run time) and trigger activity in that component.
In order to really manipulate the behavior a method (like: add automated tracing/logging code), you need something like AOP. Of course: the whole purpose of compiler-annotations are about generating code based upon the annotation. Project Lombok is a good example for such things: you put annotations into your source code, and the compiled class file contains many things inserted by Lombok during compile.
Actually,One of the basic things in OOP is IoC(Inversion of Control).We need to care this approach when building a professional application.
https://www.baeldung.com/inversion-control-and-dependency-injection-in-spring
For example,
we can write try/catch blocks in each class in the project.this is bad practice.
instead of this way ,we can use #ControllerAdvice annotation.
Just define a particular exception,JVM catch it in all the classes/requests for you.This is IoC.
You can catch exceptions in every request in project,If you define the exception in the Class which you put on the #ControllerAdvice annotation.
Simple Usage Example :
#ControllerAdvice
#RestController
public class CustomizedResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {
#ExceptionHandler(HttpRequestMethodNotSupportedException.class)
public final ResponseEntity httpRequestMethodNotSupportedException(Exception ex, WebRequest request) {
ExceptionResponse exceptionResponse = new ExceptionResponse(new Date(), "there isn’t an URL like that",
request.getDescription(false));
return new ResponseEntity<>(exceptionResponse, HttpStatus.METHOD_NOT_ALLOWED);
}
Here is the useful link about #ControllerAdvice:
https://medium.com/#jovannypcg/understanding-springs-controlleradvice-cd96a364033f
Related
I'm on learning phase of Spring boot
I've code where its written like below to handle exception in whole application. Not sure how its working, but I have NoDataFoundException class in code and its being used at place where no data found issues are happening.
#ControlAdvice
class ControllerAdvisor {
#ResponseStatus(HttpStatus.BAD_REQUEST)
#ExceptionHandler(NoDataFoundException.class)
#ResponseBody
public ResponseEntity<Object> handleNodataFoundException(
NoDataFoundException ex, WebRequest request) {
Map<String, Object> body = new LinkedHashMap<>();
body.put("timestamp", LocalDateTime.now());
body.put("message", "No cities found");
return new ResponseEntity<>(body, HttpStatus.NOT_FOUND);
}
Want to know, how and when handleNodataFoundException method automatically gets called when NoDataFoundException instance gets created ?
Does spring calls this method handleNodataFoundException on the basis of #ExceptionHandler(NoDataFoundException.class) which is bind to method itself and moreover irrespective of name of the method ?
how spring looks for parameters required for above method ? what if it has more parameters in it ?
This is done by proxying (Proxy.class).
Proxying is a mechanism in which a kind of pseudo class is created dynamically and mimics your own class (same methods) and is used to intercept all the method calls. This way it can act before and after the method calls as it please, and in the middle call the real method that you developed.
When you create a #Service in Spring, or a #Stateless in EJB, you never actually create the instances, you delegate the instance creation on the framework (Spring or EJB). Those frameworks proxy your classes and intercept every call.
In your case, and putting it simple, the proxy has a catch around the real call to your method, that catch captures exceptions, and acts upon the framework configuration built based on all the annotations that you created (#ControlAdvice, #ExceptionHandler and so on). And so it can call the handleNodataFoundException(...) in the cases that you defined with annotations.
Update visualization via stacktrace
For instance, if you have two Spring #Component (or #Service, #Repository or whatever), and one calls the other one in a plain call, and you get an exception, in the stacktrace you see plenty of method calls (involving all kind of different classes) between your two component classes, all those are proxies and framework classes that take care of proxying, invoking, configuration and all the magic that the framework does. And everything is triggered by the proxy of your second component just before calling the real code that you developed, because the first component, at execution time, doesn't really call an instance of your class, but an instance of the proxy of your class that the framework created.
If you run a plain main, with two classes calling one to the other, instantiated by you with new, you will only see 3 lines in the stacktrace, because there the instances are plain instances created by you.
I have a scenario :
UI<--->Spring boot micro-service REST API<--->server
Now, there is a situation in which I want to handle custom exceptions(which I am aware how to do) in order to return specific Http Status and message back to UI when server responds in certain manner for e.g. 500 should return "Please return after a while" insteal of "internal server error". The maven project for our micro-service is divided into 3 layers (sub maven projects) i.e. Business, Web and Domain. Where web contains controller class, Business contains Service class and Domain contains #Entity, #Components etc.
I want to know in order to handle the above mentioned exception let say HTTP Status 500, should be done at business layer? or at web layer i.e. controller level. What would be the best possible solution? (I am aware of ResponseEntity and how it can provide a customized response to UI).
I personally believe that if I include custom exception class at Business Level and return that in Controller class using response entity after checking the response status would do the trick. But officials feel that it should be done at service level? I am not able to understand why(it makes the process more complex)? can anyone suggest which solution is best?
Officials are right, it should be in Service Layer. I would say best practice would be to use #ExceptionHandler. As the downside to handling the exception in the controller method is that it makes the code less readable and might be repeated across many controller methods.
I would recommend having a base class for your controllers with the #ExceptionHandler defined. This way it can be used for many different controllers, without any code duplication. This would be more readable than the exception resolver approach, but could be used in conjunction
This is clearly explained here
If you want to handle error in a global level, you can use #ControllerAdvice which is very easy when comes to the handling custom exceptions as well as runtime exceptions.
you can throw exceptions from business layer to web controllers and define a #ControllerAdvice class to catch those errors and provide responses with correct response status.
For Ex:-
#ControllerAdvice
public class RestResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {
#ExceptionHandler(value = { IllegalArgumentException.class, IllegalStateException.class })
protected ResponseEntity<Object> handleConflict(RuntimeException ex, WebRequest request) {
String bodyOfResponse = "This should be application specific";
return handleExceptionInternal(ex, bodyOfResponse,
new HttpHeaders(), HttpStatus.CONFLICT, request);
}
}
and throw those Exception classes from the controller classes also, you dont need to catch exception from the controllers.
Hope this helps to you...
Above code snipplet i took from here
Error response is usually generated by #ExceptionHandler matching your exception type and maybe registered with #ConrtrollerAdvice as described here.
API should be standardised (e.g. http://jsonapi.org/) and designed primarily for developers. Returning "Please return after a while" instead of "Internal Server Error" makes little sense to me. It's a 500 HTTP status response of uncertain reason e.g. NullPointerException somewhere deep in the code.
I am building a Spring RESTfull service and a I have the following method that retrieves a Place object based on given zipcode:
#RequestMapping(value = "/placeByZip", method = RequestMethod.GET)
public Place getPlaceByZipcode(#RequestParam(value="zipcode") String zipcode) {
Place place = placeService.placeByZip(zipcode);
return place;
}
Is it best practice to have the return type of "Place"? I imagine this is difficult for error handling?
Using the latest versions of Spring for a RESTfull web service I do believe returning the 'Object' is good practise as it allows you to simplify your code and be specific on what you are returning. I see this as strongly typing your API response.
A good practise for error handling is to use the controller advice utility supplied by spring.
Have a read of:
https://spring.io/blog/2013/11/01/exception-handling-in-spring-mvc
This allows you to throw your exceptions at any of your service layers and produce a nice helpful error response.
A better practice would be to create a Data Transfer Object with only the properties you will be using in the front end.
With a proper JS framework you could easily do proper error handling. (for example you could define a service in AngjularJs which would define the DTO's fields).
Also, you might as well do return placeService.placeByZip(zipCode);
As robinsio suggested it is good practice to add controller advice. You can set the status to some http code (for example HttpStatus.conflict) and have an exception handler (ex. BaseServiceException) which you can throw inside your place service if some validation rules you define are broken.
The controller advice could return a map which you handle in the case of the respective http status code in a consistent manner (let's say a modal appears in the interface to notify of the message you sent from the base service exception).
So in my Service layer I have some logic that does some stuff. Sometimes it has to check to see if something is possible before it does it OR it just has to get some OK from the front end ("Are you sure you want to do this?" kind of stuff). The front end, of course, sends a transaction to the screen to get the info.
In the past I have used RuntimeExceptions for this. I will throw a
new MessageException("are.you.sure");
and then the controller level will do a
try{
theService.doSomething();
}catch(MessageException me) {
model.addAttribute(me.getMessageKey());
result.addError(new ObjectError());
}
In another application I made a PostOffice object and would put letters and such in it for messages. It was quite elaborate and very nice, but my new app is much smaller and I don't want all that.
So I am looking for some best practices. How do you guys send messages from the service layer to the front end? And keep in mind, I am NOT talking about Exceptions! I am just talking about messages from the service layer.
One beautiful thing about Spring MVC is the Exception handling. Since the DispatcherServlet has a try-catch(Exception) wrapping the handler method (ie. your controller method), it can catch all exceptions thrown and handle them with #ExceptionHandler methods or some other construct (there are alternatives).
What I've started doing is making my Service methods only throw RuntimeException instances (works well with #Transactional) and define all my #ExceptionHandler methods in a #ControllerAdvice annotated class. Something like:
#ControllerAdvice
public class ControllerHandler {
private static final Logger logger = LoggerFactory.getLogger(ControllerHandler.class);
#ExceptionHandler(value = AuthenticationException.class)
public String handleAuthenticationException(AuthenticationException e) {
if (logger.isInfoEnabled()) {
logger.info("An AuthenticationException occurred: {}", e.getMessage());
}
return "redirect:/";
}
...more
}
#ExceptionHandler annotated methods have a few rules, but are very customizable. You can see all possibilities in the javadoc here. You should also take a look at ResponseStatus.
Personally, I rarely throw checked exceptions from my service layer. The only one that often appears is IOException (parsing JSON, opening files) and even that I like to wrap in a RuntimeException, because it's not like I can do anything special about it at that level.
This has been asked a few times in Google-land, but I can't seem to apply those resolutions to my situation. My J2EE application uses Spring and I was previously using SimpleMappingExceptionResolver to intercept Exceptions to show a friendly error page for my users. One of the guys on my team has his own package and is using an extended Exception class as a vehicle to communicate validation errors to his users. So now every time a user enters invalid data, it triggers an exception page. He refuses to change his code (even though I thing he should), so now I am forced to make error handling a package- or controller-specific thing.
I've tried to leverage the #ExceptionHandler annotation to do this, but it doesn't seem to be firing. What am I doing wrong? I am expecting a call to dmapproval to essentially return the applicationError view.
Here is my controller:
#Controller
public class ExecutiveApprovalController {
/*omitted stuff*/
#ExceptionHandler(Exception.class)
public String routToErrorHandler(Exception anExc) {
return "applicationError";
}
#RequestMapping(value = "/dmapproval", method = RequestMethod.GET)
public String dmApproval(Model model, HttpServletRequest request) throws Exception {
throw new RuntimeException(); // just for testing exception logic
}
/*omitted stuff here, too*/
}
Thanks for your help!!
Your snippet looks fine; the only difference between your code and something that I have working is that I annotate the exception handler method like this:
#ExceptionHandler(Throwable.class)
As an aside; this is far less elegant than using SimpleMappingExceptionResolver (which it sounds like you already know!). I'd ask you rogue team-mate to reconsider his validation approach and use Exceptions only in exceptional circumstances ;)
Did you add this config in your servlet-context.xml
<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver">