Exception Handling In REST API

Exception is an unexpected and unwanted situation occurring in the application.

-> When exception occured our program will terminate abnormally.

-> To achieve graceful termination of the program we need to handle the exception.

-> In Java we have below keywords to handle the exceptions

1) try   :  It is used to keep risky code

2) catch  : Catch block is used to handle the exception

3) throw  : It is used to re-throw the exception

4) throws : It is used to ignore the exception

5) finally :  It is used to execute clean up logic (closing files, closing connection, release resources....)

Note: When we get exception in REST API we should convey that exception information to client / client application in json format.

Ex:

{

msg : "Exception Reason"

code : "SBI0004"

}

Note: In project, for every exception we will use one CODE i.e exception code.

-> In Spring web mvc we can handle exceptions in 2 ways.

1) Controller Based Exception Handling 

- Exception Handlers applicable for only particular controller

2) Global Exception Handling

- Exception Handlers applicable for all the classes in the project

@Data

public class ExceptionInfo {

private String msg;

private String code;

}

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@RestController

public class DemoRestController {

private Logger logger = LoggerFactory.getLogger(DemoRestController.class);

@GetMapping("/")

public String doAction() {

String msg = "Action in progress";

try {

int i = 10 / 0;

} catch (Exception e) {

logger.error("Exception Occured ::" + e, e);

throw new ArithmeticException(e.getMessage());

}

return msg;

}

@ExceptionHandler(value=ArithmeticException.class)

public ResponseEntity<ExceptionInfo> handleAE(ArithmeticException ae) {

ExceptionInfo exception = new ExceptionInfo();

exception.setMsg(ae.getMessage());

exception.setCode("AIT0004");

return new ResponseEntity<>(exception, HttpStatus.INTERNAL_SERVER_ERROR);

}

}