From Messy to Elegant: Refactoring Spring Boot Controllers with @Valid and Global Exception Handling

Spring Boot developers often encounter controllers that mix validation, logging, and business logic, leading to long, hard‑to‑read methods. The article first shows a typical “bad” controller implementation that repeats null checks, try‑catch blocks, and directly embeds service calls.

@RestController
@RequestMapping("/user/test")
public class UserController {
    private static Logger logger = LoggerFactory.getLogger(UserController.class);
    @Autowired
    private UserService userService;
    @Autowired
    private AuthService authService;
    @PostMapping
    public CommonResult userRegistration(@RequestBody UserVo userVo) {
        if (StringUtils.isBlank(userVo.getUsername())){
            return CommonResult.error("用户名不能为空");
        }
        if (StringUtils.isBlank(userVo.getPassword())){
            return CommonResult.error("密码不能为空");
        }
        logger.info("注册用户：{}", userVo.getUsername());
        try {
            userService.registerUser(userVo.getUsername());
            return CommonResult.ok();
        }catch (Exception e){
            logger.error("注册用户失败：{}", userVo.getUsername(), e);
            return CommonResult.error("注册失败");
        }
    }
    @PostMapping("/login")
    @PermitAll
    @ApiOperation("使用账号密码登录")
    public CommonResult<AuthLoginRespVO> login(@RequestBody AuthLoginReqVO reqVO) {
        if (StringUtils.isBlank(reqVO.getUsername())){
            return CommonResult.error("用户名不能为空");
        }
        if (StringUtils.isBlank(reqVO.getPassword())){
            return CommonResult.error("密码不能为空");
        }
        try {
            return success(authService.login(reqVO));
        }catch (Exception e){
            logger.error("注册用户失败：{}", reqVO.getUsername(), e);
            return CommonResult.error("注册失败");
        }
    }
}

By moving validation to the data‑transfer objects and using the @Valid annotation, the controller can be reduced to a few clear lines. The article provides a concise “good” controller example that delegates validation to the framework and leaves only service calls.

@RestController
@RequestMapping("/user/test")
public class UserController1 {
    private static Logger logger = LoggerFactory.getLogger(UserController1.class);
    @Autowired
    private UserService userService;
    @Autowired
    private AuthService authService;
    @PostMapping("/userRegistration")
    public CommonResult userRegistration(@RequestBody @Valid UserVo userVo) {
        userService.registerUser(userVo.getUsername());
        return CommonResult.ok();
    }
    @PostMapping("/login")
    @PermitAll
    @ApiOperation("使用账号密码登录")
    public CommonResult<AuthLoginRespVO> login(@RequestBody @Valid AuthLoginReqVO reqVO) {
        return success(authService.login(reqVO));
    }
}

The AuthLoginReqVO class illustrates how to apply validation annotations such as @NotEmpty , @Length , and @Pattern directly on fields, allowing Spring to automatically reject invalid requests.

@ApiModel(value = "管理后台 - 账号密码登录 Request VO")
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class AuthLoginReqVO {
    @ApiModelProperty(value = "账号", required = true, example = "user")
    @NotEmpty(message = "登录账号不能为空")
    @Length(min = 4, max = 16, message = "账号长度为 4-16 位")
    @Pattern(regexp = "^[A-Za-z0-9]+$", message = "账号格式为数字以及字母")
    private String username;

    @ApiModelProperty(value = "密码", required = true, example = "password")
    @NotEmpty(message = "密码不能为空")
    @Length(min = 4, max = 16, message = "密码长度为 4-16 位")
    private String password;
}

To handle validation failures and other runtime errors uniformly, a global exception handler is introduced. It captures MethodArgumentNotValidException to return a consolidated error message and provides a fallback handler for any uncaught exceptions.

@ResponseBody
@RestControllerAdvice
public class ExceptionHandlerAdvice {
    protected Logger logger = LoggerFactory.getLogger(getClass());

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public CommonResult
handleValidationExceptions(MethodArgumentNotValidException ex) {
        logger.error("[handleValidationExceptions]", ex);
        StringBuilder sb = new StringBuilder();
        ex.getBindingResult().getAllErrors().forEach(error -> {
            String fieldName = ((org.springframework.validation.FieldError) error).getField();
            String errorMessage = error.getDefaultMessage();
            sb.append(fieldName).append(":").append(errorMessage).append(";");
        });
        return CommonResult.error(sb.toString());
    }

    /**
     * 处理系统异常，兜底处理所有的一切
     */
    @ExceptionHandler(value = Exception.class)
    public CommonResult
defaultExceptionHandler(Throwable ex) {
        logger.error("[defaultExceptionHandler]", ex);
        // 返回 ERROR CommonResult
        return CommonResult.error(INTERNAL_SERVER_ERROR.getCode(), INTERNAL_SERVER_ERROR.getMsg());
    }
}

Adopting these practices reduces controller size by roughly half, eliminates duplicated validation code, and improves overall maintainability, making the API easier to read and extend.