SpringBoot 实战：如何优雅的处理异常

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发布于: 2020 年 10 月 10 日
前段时间写了一篇关于实现统一响应信息的博文，根据文中实战操作，能够解决正常响应的一致性，但想要实现优雅响应，还需要优雅的处理异常响应，所以有了这篇内容。
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作为后台服务，能够正确的处理程序抛出的异常，并返回友好的异常信息是非常重要的，毕竟我们大部分代码都是为了 处理异常情况。而且，统一的异常响应，有助于客户端理解服务端响应，并作出正确处理，而且能够提升接口的服务质量。
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SpringBoot提供了异常的响应，可以通过/error请求查看效果：
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这是从浏览器打开的场景，也就是请求头不包括content-type: applicaton/json，大白板一个，和友好完全不搭边。
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这是请求头包括content-type: applicaton/json时的响应，格式还行，但是我们还需要加工一下，实现自定义的异常码和异常信息。
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本文主要是针对RESTful请求的统一响应，想要实现的功能包括：
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自动封装异常，返回统一响应
异常信息国际化
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定义异常响应类﻿
当程序发送错误时，不应该将晦涩的堆栈报告信息返回给API客户端，从某种意义将，这是一种不礼貌的和不负责任的行为。
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我们在SpringBoot 实战：一招实现结果的优雅响应中，定义了一个响应类，为什么还要再定义一个异常响应类呢？其实是为了语义明确且职责单一。类图如下：
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具体代码如下：
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基础类BaseResponse：
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@Data
public abstract class BaseResponse {
    private Integer code;
    private String desc;
    private Date timestamp = new Date();
    private String path;
    public BaseResponse() {
    }
    public BaseResponse(final Integer code, final String desc) {
        this.code = code;
        this.desc = desc;
    }
    public BaseResponse(final Integer code, final String desc, final String path) {
        this.code = code;
        this.desc = desc;
        this.path = path;
    }
}
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异常类ErrorResponse：
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@EqualsAndHashCode(callSuper = true)
@Data
public class ErrorResponse extends BaseResponse {
    public ErrorResponse(final Integer code, final String desc) {
        super(code, desc);
    }
    public ErrorResponse(final Integer code, final String desc, final WebRequest request) {
        super(code, desc, extractRequestURI(request));
    }
    public ErrorResponse(final HttpStatus status, final Exception e) {
        super(status.value(), status.getReasonPhrase() + ": " + e.getMessage());
    }
    public ErrorResponse(final HttpStatus status, final Exception e, final WebRequest request) {
        super(status.value(), status.getReasonPhrase() + ": " + e.getMessage(), extractRequestURI(request));
    }
    private static String extractRequestURI(WebRequest request) {
        final String requestURI;
        if (request instanceof ServletWebRequest) {
            ServletWebRequest servletWebRequest = (ServletWebRequest) request;
            requestURI = servletWebRequest.getRequest().getRequestURI();
        } else {
            requestURI = request.getDescription(false);
        }
        return requestURI;
    }
}
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定义异常枚举类﻿
为了能够规范响应码和响应信息，我们可以定义一个枚举类。
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枚举接口ResponseEnum：
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public interface ResponseEnum {
    Integer getCode();
    String getMessage();
    default String getLocaleMessage() {
        return getLocaleMessage(null);
    }
    String getLocaleMessage(Object[] args);
}
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枚举类CommonResponseEnum：
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public enum CommonResponseEnum implements ResponseEnum {
    BAD_REQUEST(HttpStatus.BAD_REQUEST.value(), "Bad Request"),
    NOT_FOUND(HttpStatus.NOT_FOUND.value(), "Not Found"),
    METHOD_NOT_ALLOWED(HttpStatus.METHOD_NOT_ALLOWED.value(), "Method Not Allowed"),
    NOT_ACCEPTABLE(HttpStatus.NOT_ACCEPTABLE.value(), "Not Acceptable"),
    REQUEST_TIMEOUT(HttpStatus.REQUEST_TIMEOUT.value(), "Request Timeout"),
    UNSUPPORTED_MEDIA_TYPE(HttpStatus.UNSUPPORTED_MEDIA_TYPE.value(), "Unsupported Media Type"),
    INTERNAL_SERVER_ERROR(HttpStatus.INTERNAL_SERVER_ERROR.value(), "Server Error"),
    SERVICE_UNAVAILABLE(HttpStatus.SERVICE_UNAVAILABLE.value(), "Service Unavailable"),
    ILLEGAL_ARGUMENT(4000, "Illegal Argument"),
    DATA_NOT_FOUND(4004, "Data Not Found"),
    USER_NOT_FOUND(4104, "User Not Found"),
    MENU_NOT_FOUND(4204, "Menu Not Found"),
    INTERNAL_ERROR(9999, "Server Error"),
    ;
    private final Integer code;
    private final String message;
    private MessageSource messageSource;
    CommonResponseEnum(final Integer code, final String message) {
        this.code = code;
        this.message = message;
    }
    @Override
    public Integer getCode() {
        return code;
    }
    @Override
    public String getMessage() {
        return message;
    }
    @Override
    public String getLocaleMessage(Object[] args) {
        return messageSource.getMessage("response.error." + code, args, message, LocaleContextHolder.getLocale());
    }
    public void setMessageSource(final MessageSource messageSource) {
        this.messageSource = messageSource;
    }
    @Component
    public static class ReportTypeServiceInjector {
        private final MessageSource messageSource;
        public ReportTypeServiceInjector(final MessageSource messageSource) {
            this.messageSource = messageSource;
        }
        @PostConstruct
        public void postConstruct() {
            for (final CommonResponseEnum anEnum : CommonResponseEnum.values()) {
                anEnum.setMessageSource(messageSource);
            }
        }
    }
}
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需要注意的是，我们在异常枚举类中定义了ReportTypeServiceInjector类，这个类的作用是为枚举类注入MessageSource对象，是为了实现异常信息的国际化。这部分功能Spring已经封装好了，我们只需要在resources目录中定义一组messages.properties文件就可以了，比如：
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message.properties定义默认描述：
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response.error.4000=[DEFAULT] Illegal Arguments
response.error.4004=[DEFAULT] Not Found
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messageszhCN.properties定义中文描述：
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response.error.4004=对应数据未找到
response.error.9999=系统异常，请求参数: {0}
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messagesenUS.properties定义英文描述：
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response.error.4004=Not Found
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自定义异常类﻿
Java和Spring中提供了很多可用的异常类，可以满足大部分场景，但是有时候我们希望异常类可以携带更多信息，所以还是需要自定义异常类：
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可以携带我们想要的信息；
有更加明确语义；
附带效果，可以知道这是手动抛出的业务异常。
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上代码：
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@Data
@EqualsAndHashCode(callSuper = true)
public class CodeBaseException extends RuntimeException {
    private final ResponseEnum anEnum;
    private final Object[] args;// 打印参数
    private final String message;// 异常信息
    private final Throwable cause;// 异常栈
    public CodeBaseException(final ResponseEnum anEnum) {
        this(anEnum, null, anEnum.getMessage(), null);
    }
    public CodeBaseException(final ResponseEnum anEnum, final String message) {
        this(anEnum, null, message, null);
    }
    public CodeBaseException(final ResponseEnum anEnum, final Object[] args, final String message) {
        this(anEnum, args, message, null);
    }
    public CodeBaseException(final ResponseEnum anEnum, final Object[] args, final String message, final Throwable cause) {
        this.anEnum = anEnum;
        this.args = args;
        this.message = message;
        this.cause = cause;
    }
}
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自定义异常信息处理类﻿
前期准备工作完成，接下来定义异常信息处理类。
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Spring自带的异常信息处理类往往不能满足我们实际的业务需求，这就需要我们定义符合具体情况的异常信息处理类，在自定义异常信息处理类中，我们可以封装更为详细的异常报告。我们可以扩展Spring提供的ResponseEntityExceptionHandler类定义自己的异常信息处理类，站在巨人的肩膀上，快速封装自己需要的类。
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通过源码可以看到，ResponseEntityExceptionHandler类的核心方法是public final ResponseEntity<Object> handleException(Exception ex, WebRequest request)，所有的异常都在这个方法中根据类型进行处理，我们只需要实现具体的处理方法即可：
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@RestControllerAdvice
@Slf4j
public class UnifiedExceptionHandlerV2 extends ResponseEntityExceptionHandler {
    private static final String ENV_PROD = "prod";
    private final MessageSource messageSource;
    private final Boolean isProd;
    public UnifiedExceptionHandlerV2(@Value("${spring.profiles.active:dev}") final String activeProfile, final MessageSource messageSource) {
        this.messageSource = messageSource;
        this.isProd = new HashSet<>(Arrays.asList(activeProfile.split(","))).contains(ENV_PROD);
    }
    @Override
    protected ResponseEntity<Object> handleExceptionInternal(final Exception e, final Object body, final HttpHeaders headers, final HttpStatus status, final WebRequest request) {
        log.info("请求异常：" + e.getMessage(), e);
        if (HttpStatus.INTERNAL_SERVER_ERROR.equals(status)) {
            request.setAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE, e, WebRequest.SCOPE_REQUEST);
        }
        return new ResponseEntity<>(new ErrorResponse(status, e), headers, HttpStatus.OK);
    }
    @Override
    protected ResponseEntity<Object> handleBindException(final BindException ex, final HttpHeaders headers, final HttpStatus status, final WebRequest request) {
        log.info("参数绑定异常", ex);
        final ErrorResponse response = wrapperBindingResult(status, ex.getBindingResult());
        return new ResponseEntity<>(response, headers, HttpStatus.OK);
    }
    @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(final MethodArgumentNotValidException ex, final HttpHeaders headers, final HttpStatus status, final WebRequest request) {
        log.info("参数校验异常", ex);
        final ErrorResponse response = wrapperBindingResult(status, ex.getBindingResult());
        return new ResponseEntity<>(response, headers, HttpStatus.OK);
    }
    @ExceptionHandler(value = CodeBaseException.class)
    @ResponseBody
    public ErrorResponse handleBusinessException(CodeBaseException e) {
        log.error("业务异常：" + e.getMessage(), e);
        final ResponseEnum anEnum = e.getAnEnum();
        return new ErrorResponse(anEnum.getCode(), anEnum.getLocaleMessage(e.getArgs()));
    }
    @ExceptionHandler(value = Exception.class)
    @ResponseBody
    public ErrorResponse handleExceptionInternal(Exception e) {
        log.error("未捕捉异常：" + e.getMessage(), e);
        final Integer code = INTERNAL_SERVER_ERROR.getCode();
        return new ErrorResponse(code, getLocaleMessage(code, e.getMessage()));
    }
    /**
     * 包装绑定异常结果
     *
     * @param status        HTTP状态码
     * @param bindingResult 参数校验结果
     * @return 异常对象
     */
    private ErrorResponse wrapperBindingResult(HttpStatus status, BindingResult bindingResult) {
        final List<String> errorDesc = new ArrayList<>();
        for (ObjectError error : bindingResult.getAllErrors()) {
            final StringBuilder msg = new StringBuilder();
            if (error instanceof FieldError) {
                msg.append(((FieldError) error).getField()).append(": ");
            }
            msg.append(error.getDefaultMessage() == null ? "" : error.getDefaultMessage());
            errorDesc.add(msg.toString());
        }
        final String desc = isProd ? getLocaleMessage(status.value(), status.getReasonPhrase()) : String.join(", ", errorDesc);
        return new ErrorResponse(status.value(), desc);
    }
    private String getLocaleMessage(Integer code, String defaultMsg) {
        try {
            return messageSource.getMessage("" + code, null, defaultMsg, LocaleContextHolder.getLocale());
        } catch (Throwable t) {
            log.warn("本地化异常消息发生异常: {}", code);
            return defaultMsg;
        }
    }
}
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如果感觉Spring的ResponseEntityExceptionHandler类不够灵活，也可以完全自定义异常处理类：
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@RestControllerAdvice
@Slf4j
public class UnifiedExceptionHandler {
    private static final String ENV_PROD = "prod";
    private final MessageSource messageSource;
    private final Boolean isProd;
    public UnifiedExceptionHandler(@Value("${spring.profiles.active:dev}") final String activeProfile, final MessageSource messageSource) {
        this.messageSource = messageSource;
        this.isProd = new HashSet<>(Arrays.asList(activeProfile.split(","))).contains(ENV_PROD);
    }
    @ExceptionHandler({
            MissingServletRequestParameterException.class,// 缺少servlet请求参数异常处理方法
            ServletRequestBindingException.class,// servlet请求绑定异常
            TypeMismatchException.class,// 类型不匹配
            HttpMessageNotReadableException.class,// 消息无法检索
            MissingServletRequestPartException.class// 缺少servlet请求部分
    })
    public ErrorResponse badRequestException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(BAD_REQUEST.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            NoHandlerFoundException.class// 没有发现处理程序异常
    })
    public ErrorResponse noHandlerFoundException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(NOT_FOUND.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            HttpRequestMethodNotSupportedException.class// 不支持的HTTP请求方法异常信息处理方法
    })
    public ErrorResponse httpRequestMethodNotSupportedException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(METHOD_NOT_ALLOWED.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            HttpMediaTypeNotAcceptableException.class// 不接受的HTTP媒体类型异常处方法
    })
    public ErrorResponse httpMediaTypeNotAcceptableException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(NOT_ACCEPTABLE.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            HttpMediaTypeNotSupportedException.class// 不支持的HTTP媒体类型异常处理方法
    })
    public ErrorResponse httpMediaTypeNotSupportedException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(UNSUPPORTED_MEDIA_TYPE.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            AsyncRequestTimeoutException.class// 异步请求超时异常
    })
    public ErrorResponse asyncRequestTimeoutException(Exception e, WebRequest request) {
        log.info(e.getMessage(), e);
        return new ErrorResponse(SERVICE_UNAVAILABLE.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            MissingPathVariableException.class,// 请求路径参数缺失异常处方法
            HttpMessageNotWritableException.class,// HTTP消息不可写
            ConversionNotSupportedException.class,// 不支持转换
    })
    public ErrorResponse handleServletException(Exception e, WebRequest request) {
        log.error(e.getMessage(), e);
        return new ErrorResponse(INTERNAL_SERVER_ERROR.getCode(), e.getMessage(), request);
    }
    @ExceptionHandler({
            BindException.class// 参数绑定异常
    })
    @ResponseBody
    public ErrorResponse handleBindException(BindException e, WebRequest request) {
        log.error("参数绑定异常", e);
        return wrapperBindingResult(e.getBindingResult(), request);
    }
    /**
     * 参数校验异常，将校验失败的所有异常组合成一条错误信息
     */
    @ExceptionHandler({
            MethodArgumentNotValidException.class// 方法参数无效
    })
    @ResponseBody
    public ErrorResponse handleValidException(MethodArgumentNotValidException e, WebRequest request) {
        log.error("参数校验异常", e);
        return wrapperBindingResult(e.getBindingResult(), request);
    }
    /**
     * 包装绑定异常结果
     */
    private ErrorResponse wrapperBindingResult(BindingResult bindingResult, WebRequest request) {
        final List<String> errorDesc = new ArrayList<>();
        for (ObjectError error : bindingResult.getAllErrors()) {
            final StringBuilder msg = new StringBuilder();
            if (error instanceof FieldError) {
                msg.append(((FieldError) error).getField()).append(": ");
            }
            msg.append(error.getDefaultMessage() == null ? "" : error.getDefaultMessage());
            errorDesc.add(msg.toString());
        }
        final String desc = isProd ? getLocaleMessage(BAD_REQUEST.getCode(), "") : String.join(", ", errorDesc);
        return new ErrorResponse(BAD_REQUEST.getCode(), desc, request);
    }
    /**
     * 业务异常
     */
    @ExceptionHandler(value = CodeBaseException.class)
    @ResponseBody
    public ErrorResponse handleBusinessException(CodeBaseException e, WebRequest request) {
        log.error("业务异常：" + e.getMessage(), e);
        final ResponseEnum anEnum = e.getAnEnum();
        return new ErrorResponse(anEnum.getCode(), anEnum.getLocaleMessage(e.getArgs()), request);
    }
    /**
     * 未定义异常
     */
    @ExceptionHandler(value = Exception.class)
    @ResponseBody
    public ErrorResponse handleExceptionInternal(Exception e, WebRequest request) {
        log.error("未捕捉异常：" + e.getMessage(), e);
        final Integer code = INTERNAL_SERVER_ERROR.getCode();
        return new ErrorResponse(code, getLocaleMessage(code, e.getMessage()), request);
    }
    private String getLocaleMessage(Integer code, String defaultMsg) {
        try {
            return messageSource.getMessage("" + code, null, defaultMsg, LocaleContextHolder.getLocale());
        } catch (Throwable t) {
            log.warn("本地化异常消息发生异常: {}", code);
            return defaultMsg;
        }
    }
}
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从上面两个类可以看出，比较核心的是这么几个注解：
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@ExceptionHandle：负责处理controller标注的类中抛出的异常的注解
@RestControllerAdvice：能够将@ExceptionHandler标注的方法集中到一个地方进行处理的注解，这个注解是复合注解，实现了@ControllerAdvice和@ResponseBody的功能。
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借用谭朝红博文中的图片（蓝色箭头表示正常的请求和响应，红色箭头表示发生异常的请求和响应）：
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写个Demo测试一下﻿
接下来我们写个demo测试一下是否能够实现异常的优雅响应：
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@RestController
@RequestMapping("index")
@Slf4j
public class IndexController {
    private final IndexService indexService;
    public IndexController(final IndexService indexService) {
        this.indexService = indexService;
    }
    @GetMapping("hello1")
    public Response<String> hello1() {
        Response<String> response = new Response<>();
        try {
            response.setCode(200);
            response.setDesc("请求成功");
            response.setData(indexService.hello());
        } catch (Exception e) {
            log.error("hello1方法请求异常", e);
            response.setCode(500);
            response.setDesc("请求异常:" + e.getMessage());
        } finally {
            log.info("执行controller的finally结构");
        }
        return response;
    }
    @GetMapping("hello2")
    public Response<String> hello2(@RequestParam("ex") String ex) {
        switch (ex) {
            case "ex1":
                throw new CodeBaseException(CommonResponseEnum.USER_NOT_FOUND, "用户信息不存在");
            case "ex2":
                throw new CodeBaseException(CommonResponseEnum.MENU_NOT_FOUND, "菜单信息不存在");
            case "ex3":
                throw new CodeBaseException(CommonResponseEnum.ILLEGAL_ARGUMENT, "请求参数异常");
            case "ex4":
                throw new CodeBaseException(CommonResponseEnum.DATA_NOT_FOUND, "数据不存在");
        }
        throw new CodeBaseException(INTERNAL_ERROR, new Object[]{ex}, "请求异常", new RuntimeException("运行时异常信息"));
    }
}
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启动服务之后，传入不同参数获取不同的异常信息：
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// 请求 /index/hello2?ex=ex1
{
    "code": 4104,
    "desc": "User Not Found",
    "timestamp": "2020-10-10T05:58:39.433+00:00",
    "path": "/index/hello2"
}
// 请求 /index/hello2?ex=ex2
{
    "code": 4204,
    "desc": "Menu Not Found",
    "timestamp": "2020-10-10T06:00:34.141+00:00",
    "path": "/index/hello2"
}
// 请求 /index/hello2?ex=ex3
{
    "code": 4000,
    "desc": "[DEFAULT] Illegal Arguments",
    "timestamp": "2020-10-10T06:00:44.233+00:00",
    "path": "/index/hello2"
}
// 请求 /index/hello2?ex=ex4
{
    "code": 4004,
    "desc": "对应数据未找到",
    "timestamp": "2020-10-10T06:00:54.178+00:00",
    "path": "/index/hello2"
}
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附上文中的代码：<https://github.com/howardliu-cn/effective-spring/tree/main/spring-exception-handler>，收工。
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个人主页: <https://www.howardliu.cn>
个人博文: SpringBoot 实战：如何优雅的处理异常
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