PYTHON

Handling Exceptions

>>> while True:
...     try:
...         x = int(input("Please enter a number: "))
...         break
...     except ValueError:
...         print("Oops!  That was no valid number.  Try again...")
...

Handling Exceptions

import sys

try:
    f = open('myfile.txt')
    s = f.readline()
    i = int(s.strip())
except IOError as err:
    print("I/O error: {0}".format(err))
except ValueError:
    print("Could not convert data to an integer.")
except:
    print("Unexpected error:", sys.exc_info()[0])
    raise

Handling Exceptions

for arg in sys.argv[1:]:
    try:
        f = open(arg, 'r')
    except IOError:
        print('cannot open', arg)
    else:
        print(arg, 'has', len(f.readlines()), 'lines')
        f.close()

exception handling

#include <iostream>
#include<conio.h>
using namespace std;
int main()
{
    int a=10, b=0, c;
    // try block activates exception handling
    try 
    {
        if(b == 0)
        {
            // throw custom exception
            throw "Division by zero not possible";
            c = a/b;
        }
    }
    catch(char* ex) // catches exception
    {
        cout<<ex;
    }
    return 0;
}

Handling Exceptions

... except (RuntimeError, TypeError, NameError):
...     pass

Handling Exceptions

>>> try:
...    raise Exception('spam', 'eggs')
... except Exception as inst:
...    print(type(inst))    # the exception instance
...    print(inst.args)     # arguments stored in .args
...    print(inst)          # __str__ allows args to be printed directly,
...                         # but may be overridden in exception subclasses
...    x, y = inst.args     # unpack args
...    print('x =', x)
...    print('y =', y)
...
<class 'Exception'>
('spam', 'eggs')
('spam', 'eggs')
x = spam
y = eggs

Handling Exceptions

>>> def this_fails():
...     x = 1/0
...
>>> try:
...     this_fails()
... except ZeroDivisionError as err:
...     print('Handling run-time error:', err)
...
Handling run-time error: int division or modulo by zero

exception handling

@RestController
@RequestMapping("/product")
@AllArgsConstructor
public class ProductController {
  public static final String TRACE = "trace";

  @Value("${reflectoring.trace:false}")
  private boolean printStackTrace;
  
  private final ProductService productService;

  @GetMapping("/{id}")
  public Product getProduct(@PathVariable String id){
    return productService.getProduct(id);
  }

  @PostMapping
  public Product addProduct(@RequestBody @Valid ProductInput input){
    return productService.addProduct(input);
  }

  @ExceptionHandler(NoSuchElementFoundException.class)
  @ResponseStatus(HttpStatus.NOT_FOUND)
  public ResponseEntity<ErrorResponse> handleItemNotFoundException(
      NoSuchElementFoundException exception, 
      WebRequest request
  ){
    log.error("Failed to find the requested element", exception);
    return buildErrorResponse(exception, HttpStatus.NOT_FOUND, request);
  }

  @ExceptionHandler(MethodArgumentNotValidException.class)
  @ResponseStatus(HttpStatus.UNPROCESSABLE_ENTITY)
  public ResponseEntity<ErrorResponse> handleMethodArgumentNotValid(
      MethodArgumentNotValidException ex,
      WebRequest request
  ) {
    ErrorResponse errorResponse = new ErrorResponse(
        HttpStatus.UNPROCESSABLE_ENTITY.value(), 
        "Validation error. Check 'errors' field for details."
    );
    
    for (FieldError fieldError : ex.getBindingResult().getFieldErrors()) {
      errorResponse.addValidationError(fieldError.getField(), 
          fieldError.getDefaultMessage());
    }
    return ResponseEntity.unprocessableEntity().body(errorResponse);
  }

  @ExceptionHandler(Exception.class)
  @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
  public ResponseEntity<ErrorResponse> handleAllUncaughtException(
      Exception exception, 
      WebRequest request){
    log.error("Unknown error occurred", exception);
    return buildErrorResponse(
        exception,
        "Unknown error occurred", 
        HttpStatus.INTERNAL_SERVER_ERROR, 
        request
    );
  }

  private ResponseEntity<ErrorResponse> buildErrorResponse(
      Exception exception,
      HttpStatus httpStatus,
      WebRequest request
  ) {
    return buildErrorResponse(
        exception, 
        exception.getMessage(), 
        httpStatus, 
        request);
  }

  private ResponseEntity<ErrorResponse> buildErrorResponse(
      Exception exception,
      String message,
      HttpStatus httpStatus,
      WebRequest request
  ) {
    ErrorResponse errorResponse = new ErrorResponse(
        httpStatus.value(), 
        exception.getMessage()
    );
    
    if(printStackTrace && isTraceOn(request)){
      errorResponse.setStackTrace(ExceptionUtils.getStackTrace(exception));
    }
    return ResponseEntity.status(httpStatus).body(errorResponse);
  }

  private boolean isTraceOn(WebRequest request) {
    String [] value = request.getParameterValues(TRACE);
    return Objects.nonNull(value)
        && value.length > 0
        && value[0].contentEquals("true");
  }
}

handling exceptions

I use try & catch & finally block
to handle exception if I will use the method
in different class.

Or If I will use it only once and if it is checked
exception then I use THROWS keyword on method signature