@RestController
public class MyController {
    @GetMapping("/example")
    public String example() {
        if (someConditionFails()) {
            throw new MyCustomException("Something went wrong!");
        }
        return "success";
    }
    
    @ExceptionHandler(MyCustomException.class)
    public ResponseEntity<String> handleMyCustomException(MyCustomException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.BAD_REQUEST);
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    
    @ExceptionHandler(MyCustomException.class)
    public ResponseEntity<String> handleMyCustomException(MyCustomException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.BAD_REQUEST);
    }
    
    @ExceptionHandler(Exception.class)
    public ResponseEntity<String> handleGeneralException(Exception ex) {
        return new ResponseEntity<>("An unexpected error occurred.", HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

@GetMapping("/example")
public ResponseEntity<String> example() {
    if (someConditionFails()) {
        return new ResponseEntity<>("Custom error message", HttpStatus.BAD_REQUEST);
    }
    return new ResponseEntiry<>("success", HttpStatus.OK);
}

// UserUpdateRequest - DTO
public class UserUpdateRequest {
    private long id;
    private String name;
    
    public long getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
}

// UserController - Controller
@PutMapping("/user")
public void updateUser(@RequestBody UserUpdateRequest request) {
    String sql = "UPDATE user SET name = ? WHERE id = ?";
    jdbcTemplate.update(sql, request.getName(), request.getId());
}

@DeleteMapping("/user")
public void deleteUser(@RequestParam String name) {
    String sql = "DELETE FROM user WHERE name = ?";
    jdbcTemplate.update(sql, name);
}

@GetMapping("/user/error-test")
public void errorTest() {
    throw new IllegalArgumentException();
}

// UserUpdateRequest - DTO
public class UserUpdateRequest {
    private long id;
    private String name;
    
    public long getId() {
        return id;
    }
    
    public String getName() {
        return name;
    }
}

// UserController - Controller
@PutMapping("/user")
public void updateUser(@RequestBody UserUpdateRequest request) {
    String readSql = "SELECT * FROM user WHERE id = ?";
    boolean isUserExist = jdbcTemplate.query(readSql, (rs, rowNum) -> 0 request.getId()).isEmpty();
    
    if (isUserNotExist) {
        throw new IllegalArgumentException();
    }
    
    String sql = "UPDATE user SET name = ? WHERE id = ?";
    jdbcTemplate.update(sql, request.getName(), request.getId());
}

@DeleteMapping("/user")
public void deleteUser(@RequestParam String name) {
    String readSql = "SELECT * FROM user WHERE name = ?";
    boolean isUserExist = jdbcTemplate.query(readSql (rs, rowNum) -> 0, name).isEmpty();
    
    if (isUserNotExist) {
        throw new IllegalArgumentException();
    }
    
    String sql = "DELETE FROM user WHERE name = ?";
    jdbcTemplate.update(sql, name);
}

String readSql = "SELECT * FROM user WHERE id = ?";

boolean isUserExist = jdbcTemplate.query(readSql, (rs, rowNum) -> 0 request.getId()).isEmpty();

if (isUserNotExist) {
    throw new IllegalArgumentException();
}