Exception Handler

• Exception handler in spring MVC is use to control the exceptions in our code.
• To learn more about exception hanlder you can look at here

Using Exception Handler

Throw Exception:

• In your controller method:

    @RequestMapping(value = "/user/profile/{id}", method = RequestMethod.GET)
    public String getUserProfile(@ModelAttribute("account") Account account, @PathVariable("id") String id, Model model){
        account = service.getUserProfile(id);
        if(account == null || account.getId() == null)
            throw new RuntimeException();
        model.addAttribute("statuses", EnrollStatus.values());
        return "account/userprofile";
    }

• You can throw another exceptions such as: NullPointerException, SQLException etc.

Exception Handler:

• In the controller class you declare an method to control exception with annotation @ExceptionHandler

    @ExceptionHandler(NullPointerException.class)
    public String exceptionControl(){
        return "exceptions/controllerExceptionHandler";
    }

• In @ExceptionHandler(NullPointerException.class) the NullPointerException.class is use to specify the method that will be calll when you throw an exception.
• You can you another exception class such as: SQLException.class, DataAccessException.class, Exception.class, etc.
• Or you can declare an custom exception class by RuntimeException base class:

public class HttpExceptionHanler extends RuntimeException {
    private String errorCode;
    private String errorMessage;

    public String getErrorCode() {
        return errorCode;
    }

    public void setErrorCode(String errorCode) {
        this.errorCode = errorCode;
    }

    public String getErrorMessage() {
        return errorMessage;
    }

    public void setErrorMessage(String errorMessage) {
        this.errorMessage = errorMessage;
    }

    public HttpExceptionHanler(String errorCode, String errorMessage) {
        this.errorCode = errorCode;
        this.errorMessage = errorMessage;
    }
}

• If you want use global exception handle to handle an same exception form many controller you can declare an class that implement Spring MVC Exception Handle Abtract classes.
• When you declare an exception class you must mark that class is an Bean object.

@Component
public class GlobalException implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        ModelAndView view = new ModelAndView();
        view.setViewName("exceptions/globalExceptionHandler");
        return view;
    }
}

• Or using @ControllerAdvice annotation:

@ControllerAdvice
class GlobalException {
    @ResponseStatus(HttpStatus.CONFLICT)  // 409
    @ExceptionHandler(DataIntegrityViolationException.class)
    public void handleConflict() {
        // Do something
    }
}