异常处理总结

自定义异常

​ 系统中的异常可以分为我们能预知的异常和未知的系统异常，对于我们能预知的异常如空值判断，用户名错误，密码错误等异常我们需要返回客户端，对于系统内部异常如SQL语法错误，参数格式转换错误等需要统一包装成友好的提示后再返回客户端，否则用户也看不懂系统内部的异常。

定义响应码ResponseCode ，方便之后的自定义异常

public enum ResponseCode {
    RESPONSE_CODE_200(200, "操作成功"),
    RESPONSE_CODE_400(400, "参数错误"),
    RESPONSE_CODE_1001(1001, "激活失败已过期"),
    RESPONSE_CODE_1002(1002, "密码不一致")

    private Integer code;
    private String message;
    
    ResponseCode(Integer code, String message) {
        this.code = code;
        this.message = message;
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

定义已知异常BusinessException，用于区分项目中的已知异常和未知异常

public class BusinessException extends RuntimeException{
    private Integer code;

    public BusinessException(ResponseCode responseCode) {
        super(responseCode.getMessage());
        this.code = responseCode.getCode();
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }

    public BusinessException() {
        super();
    }

    public BusinessException(String s) {
        super(s);
    }

    public BusinessException(String message, Throwable cause) {
        super(message, cause);
    }

    public BusinessException(Throwable cause) {
        super(cause);
    }

    protected BusinessException(String message, Throwable cause,
                                boolean enableSuppression,
                                boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}

自定义断言工具类，避免大量if判断

public class AssertUtils {

    public static void isTrue(Boolean flag, ResponseCode responseCode) {
        if (!flag) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isBlank(String str, ResponseCode responseCode) {
        if (StrUtil.isNotBlank(str)) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isNotBlank(String str, ResponseCode responseCode) {
        if (StrUtil.isBlank(str)) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isNull(Object object, ResponseCode responseCode) {
        if (Objects.nonNull(object)) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isNotNull(Object object, ResponseCode responseCode) {
        if (Objects.isNull(object)) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isNull(Collection collection, ResponseCode responseCode) {
        if (collection != null && !collection.isEmpty()) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isNotNull(Collection collection, ResponseCode responseCode) {
        if (collection == null || collection.isEmpty()) {
            throw new BusinessException(responseCode);
        }
    }

    public static void isEq(String str1, String st2, ResponseCode responseCode) {
        if (!str1.equals(st2)) {
            throw new BusinessException(responseCode);
        }
    }


    public static void isEqIgnoreCase(String str1, String str2, ResponseCode responseCode) {
        if (!str1.equalsIgnoreCase(str2)) {
            throw new BusinessException(responseCode);
        }
    }

    public static void smallerThan(Long second, int i, ResponseCode responseCode) {
        if (second > i) {
            throw new BusinessException(responseCode);
        }
    }
}

全局异常处理类，不再写大量try - catch，由全局异常处理类自动捕获

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(BusinessException.class)
    public AjaxResult businessExceptionHandler(BusinessException e) {
        e.printStackTrace();
        return AjaxResult.me()
                .setSuccess(false)
                .setMessage(e.getMessage())
                .setCode(e.getCode());
    }
	
	//JSR-303校验所抛出的异常
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public AjaxResult MethodArgumentNotValidExceptionHandler(MethodArgumentNotValidException e) {
        e.printStackTrace();
        BindingResult bindingResult = e.getBindingResult();
        List<ObjectError> allErrors = bindingResult.getAllErrors();
        StringBuffer sb = new StringBuffer();
        allErrors.forEach(objectError -> sb.append(objectError.getDefaultMessage()).append("! "));
        return AjaxResult.me()
                .setSuccess(false)
                .setMessage(sb.toString())
                .setCode(ResponseCode.RESPONSE_CODE_400.getCode());
    }

    @ExceptionHandler(Exception.class)
    public AjaxResult ExceptionHandler(Exception e) {
        e.printStackTrace();
        return AjaxResult.me()
                .setSuccess(false)
                .setMessage(ResponseCode.RESPONSE_CODE_500.getMessage())
                .setCode(ResponseCode.RESPONSE_CODE_500.getCode());
    }
}

在使用dto接受前端参数时，可以使用JSR-303校验

@Data
public class PlaceOrderDTO {

    private String parentOrderNo;

    @NotNull(message = "请选择收货地址") // 当为空时会报错 -> "请选择收货地址"
    private OrderGiftAddress address;

}

可以将异常信息定义在properties中在resources包下ValidationMessages.properties配置文件中，将中文转换为Unicode转义序列的UTF-16编码格式

example.error.blank     = \u4e0d\u80fd\u4e3a\u7a7a
\u4e0d 表示中文字符“不”。
\u80fd 表示中文字符“能”。
\u4e3a 表示中文字符“为”。
\u7a7a 表示中文字符“空”。

ValidationMessages.properties配置文件原本是在org.hibernate.validator包下的，因为javaapi中只定义了jsr303规范，具体实现是由其他包实现的，springboot-starter下是由org.hibernate.validator来实现的

@NotBlank(message = "${example.error.blank}")
   private String username;
    

在controller接口参数位置打上@Valid，JSR303才能生效

 @PostMapping("/placeorder")
    public AjaxResult placeOrder(@Valid @RequestBody PlaceOrderDTO dto) {
        orderGiftService.placeOrder(dto);
        return AjaxResult.me().setResultObj(dto.getUniPayOrderSn());
    }
    ```