How to correctly handle exceptions from the service (spring boot rest) - spring-boot

Question

When building a rest api using spring boot what is the best way to handle exceptions from the service level and pass them to the controller, so the client gets a custom json error message.
{
"message": "some error"
}
Endpoint from controller
#PostMapping("/login")
public String login(#RequestBody #Valid LoginDto loginDto) {
return gson.toJson(userService.login(loginDto.getUsername(), loginDto.getPassword()));
}
Service level code
public LoginResponseDto login(String username, String password) {
try {
//performs some checks
...
return new LoginResponseDto(token.get());
} catch (AuthenticationException e){
LOGGER.info("Log in failed for user {}", username);
}
return new LoginResponseDto("login failed");
}
LoginResponseDto class
String token;
String message;
public LoginResponseDto(String message) {
this.message = message;
}
Currently it is obviously returning the correctly message but not the correct status code, it will show status 200 with the error message in json.

Answer 1

You have some options:
1) Returning a message:
If you want to return a message something like this,
{
"message": "some error"
}
What you can do is:
Option 1: Create a custom POJO class for error message and return the reference to the object of that POJO class.
Something like this:
ErrorMessage.java
package org.example;
public class ErrorMessage {
private String message;
public ErrorMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
}
Request Handler Method in Controller:
#GetMapping("/login{?username, password}")
public ErrorMessage isUserAuthenticated(#RequestParam String username, #RequestParam String password) {
if (username.toLowerCase().contentEquals("root") && password.contentEquals("system")) {
return new ErrorMessage("authenticated");
}
return null;
}
Option 2: Create a Map and insert key-value pairs that you want to have in the message.
Like this:
#GetMapping("/login{?username, password}")
public Map<String, String> isUserAuthenticated(#RequestParam String username, #RequestParam String password) {
Map<String, String> message = new HashMap<>();
if (username.toLowerCase().contentEquals("root") && password.contentEquals("system")) {
message.put("message", "authenticated");
}
return message;
}
2) Returning an error status code (highly recommended by me):
You may use ResponseEntity for this purpose.
#GetMapping("/login{?username, password}")
public ResponseEntity<?> isUserAuthenticated(#RequestParam String username, #RequestParam String password) {
if (username.toLowerCase().contentEquals("root") && password.contentEquals("system")) {
return new ResponseEntity<>(HttpStatus.OK);
}
return new ResponseEntity<>(HttpStatus.NOT_FOUND);
}