SpringBoot接口 - 如何统一异常处理

arcstack约 1960 字大约 7 分钟

SpringBoot接口 - 如何统一异常处理

SpringBoot接口如何对异常进行统一封装，并统一返回呢？以上文的参数校验为例，如何优雅的将参数校验的错误信息统一处理并封装返回呢？@pdai

SpringBoot接口 - 如何统一异常处理
为什么要优雅的处理异常
实现案例
@ControllerAdvice异常统一处理
Controller接口
运行测试
进一步理解
@ControllerAdvice还可以怎么用？
@ControllerAdvice是如何起作用的（原理）？
示例源码

为什么要优雅的处理异常

如果我们不统一的处理异常，经常会在controller层有大量的异常处理的代码，比如：

    @Slf4j
    @Api(value = "User Interfaces", tags = "User Interfaces")
    @RestController
    @RequestMapping("/user")
    public class UserController {

        /** * http://localhost:8080/user/add . * * @param userParam user param * @return user */
        @ApiOperation("Add User")
        @ApiImplicitParam(name = "userParam", type = "body", dataTypeClass = UserParam.class, required = true)
        @PostMapping("add")
        public ResponseEntity<String> add(@Valid @RequestBody UserParam userParam) {
            // 每个接口充斥着大量的异常处理
            try {
                // do something
            } catch(Exception e) {
                return ResponseEntity.fail("error");
            }
            return ResponseEntity.ok("success");
        }
    }

那怎么实现统一的异常处理，特别是结合参数校验等封装？

实现案例

简单展示通过@ControllerAdvice进行统一异常处理。

@ControllerAdvice异常统一处理

对于400参数错误异常

    /** * Global exception handler. * * @author pdai */
    @Slf4j
    @RestControllerAdvice
    public class GlobalExceptionHandler {

        /** * exception handler for bad request. * * @param e * exception * @return ResponseResult */
        @ResponseBody
        @ResponseStatus(code = HttpStatus.BAD_REQUEST)
        @ExceptionHandler(value = { BindException.class, ValidationException.class, MethodArgumentNotValidException.class })
        public ResponseResult<ExceptionData> handleParameterVerificationException(@NonNull Exception e) {
            ExceptionData.ExceptionDataBuilder exceptionDataBuilder = ExceptionData.builder();
            log.warn("Exception: {}", e.getMessage());
            if (e instanceof BindException) {
                BindingResult bindingResult = ((MethodArgumentNotValidException) e).getBindingResult();
                bindingResult.getAllErrors().stream().map(DefaultMessageSourceResolvable::getDefaultMessage)
                        .forEach(exceptionDataBuilder::error);
            } else if (e instanceof ConstraintViolationException) {
                if (e.getMessage() != null) {
                    exceptionDataBuilder.error(e.getMessage());
                }
            } else {
                exceptionDataBuilder.error("invalid parameter");
            }
            return ResponseResultEntity.fail(exceptionDataBuilder.build(), "invalid parameter");
        }

    }

对于自定义异常

    /** * handle business exception. * * @param businessException * business exception * @return ResponseResult */
    @ResponseBody
    @ExceptionHandler(BusinessException.class)
    public ResponseResult<BusinessException> processBusinessException(BusinessException businessException) {
        log.error(businessException.getLocalizedMessage(), businessException);
        // 这里可以屏蔽掉后台的异常栈信息，直接返回"business error"
        return ResponseResultEntity.fail(businessException, businessException.getLocalizedMessage());
    }

对于其它异常

    /** * handle other exception. * * @param exception * exception * @return ResponseResult */
    @ResponseBody
    @ExceptionHandler(Exception.class)
    public ResponseResult<Exception> processException(Exception exception) {
        log.error(exception.getLocalizedMessage(), exception);
        // 这里可以屏蔽掉后台的异常栈信息，直接返回"server error"
        return ResponseResultEntity.fail(exception, exception.getLocalizedMessage());
    }

Controller接口

（接口中无需处理异常）

    @Slf4j
    @Api(value = "User Interfaces", tags = "User Interfaces")
    @RestController
    @RequestMapping("/user")
    public class UserController {

        /** * http://localhost:8080/user/add . * * @param userParam user param * @return user */
        @ApiOperation("Add User")
        @ApiImplicitParam(name = "userParam", type = "body", dataTypeClass = UserParam.class, required = true)
        @PostMapping("add")
        public ResponseEntity<UserParam> add(@Valid @RequestBody UserParam userParam) {
            return ResponseEntity.ok(userParam);
        }
    }

运行测试

这里用postman测试下

进一步理解

我们再通过一些问题来帮助你更深入理解@ControllerAdvice。@pdai

@ControllerAdvice还可以怎么用？

除了通过@ExceptionHandler注解用于全局异常的处理之外，@ControllerAdvice还有两个用法：

@InitBinder注解

用于请求中注册自定义参数的解析，从而达到自定义请求参数格式的目的；比如，在@ControllerAdvice注解的类中添加如下方法，来统一处理日期格式的格式化

    @InitBinder
    public void handleInitBinder(WebDataBinder dataBinder){
        dataBinder.registerCustomEditor(Date.class,
                new CustomDateEditor(new SimpleDateFormat("yyyy-MM-dd"), false));
    }

Controller中传入参数（string类型）自动转化为Date类型

    @GetMapping("testDate")
    public Date processApi(Date date) {
        return date;
    }

@ModelAttribute注解

用来预设全局参数，比如最典型的使用Spring Security时将添加当前登录的用户信息（UserDetails)作为参数。

    @ModelAttribute("currentUser")
    public UserDetails modelAttribute() {
        return (UserDetails) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
    }

所有controller类中requestMapping方法都可以直接获取并使用currentUser

    @PostMapping("saveSomething")
    public ResponseEntity<String> saveSomeObj(@ModelAttribute("currentUser") UserDetails operator) {
        // 保存操作，并设置当前操作人员的ID（从UserDetails中获得）
        return ResponseEntity.success("ok");
    }

@ControllerAdvice是如何起作用的（原理）？

我们在Spring基础 - SpringMVC案例和机制的基础上来看@ControllerAdvice的源码实现。 DispatcherServlet中onRefresh方法是初始化ApplicationContext后的回调方法，它会调用initStrategies方法，主要更新一些servlet需要使用的对象，包括国际化处理，requestMapping，视图解析等等。

    /** * This implementation calls {@link #initStrategies}. */
    @Override
    protected void onRefresh(ApplicationContext context) {
        initStrategies(context);
    }

    /** * Initialize the strategy objects that this servlet uses. * <p>May be overridden in subclasses in order to initialize further strategy objects. */
    protected void initStrategies(ApplicationContext context) {
        initMultipartResolver(context); // 文件上传
        initLocaleResolver(context); // i18n国际化
        initThemeResolver(context); // 主题
        initHandlerMappings(context); // requestMapping
        initHandlerAdapters(context); // adapters
        initHandlerExceptionResolvers(context); // 异常处理
        initRequestToViewNameTranslator(context);
        initViewResolvers(context);
        initFlashMapManager(context);
    }

从上述代码看，如果要提供@ControllerAdvice提供的三种注解功能，从设计和实现的角度肯定是实现的代码需要放在initStrategies方法中。

@ModelAttribute和@InitBinder处理

具体来看，如果你是设计者，很显然容易想到：对于@ModelAttribute提供的参数预置和@InitBinder注解提供的预处理方法应该是放在一个方法中的，因为它们都是在进入requestMapping方法前做的操作。如下方法是获取所有的HandlerAdapter，无非就是从BeanFactory中获取（BeanFactory相关知识请参考 Spring进阶- Spring IOC实现原理详解之IOC体系结构设计 )

    private void initHandlerAdapters(ApplicationContext context) {
        this.handlerAdapters = null;

        if (this.detectAllHandlerAdapters) {
            // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
            Map<String, HandlerAdapter> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerAdapters = new ArrayList<>(matchingBeans.values());
                // We keep HandlerAdapters in sorted order.
                AnnotationAwareOrderComparator.sort(this.handlerAdapters);
            }
        }
        else {
            try {
                HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
                this.handlerAdapters = Collections.singletonList(ha);
            }
            catch (NoSuchBeanDefinitionException ex) {
                // Ignore, we'll add a default HandlerAdapter later.
            }
        }

        // Ensure we have at least some HandlerAdapters, by registering
        // default HandlerAdapters if no other adapters are found.
        if (this.handlerAdapters == null) {
            this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
            if (logger.isTraceEnabled()) {
                logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
                        "': using default strategies from DispatcherServlet.properties");
            }
        }
    }

我们要处理的是requestMapping的handlerResolver，作为设计者，就很容易出如下的结构

在RequestMappingHandlerAdapter中的afterPropertiesSet去处理advice

    @Override
    public void afterPropertiesSet() {
        // Do this first, it may add ResponseBody advice beans
        initControllerAdviceCache();

        if (this.argumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
            this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        if (this.initBinderArgumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
            this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        if (this.returnValueHandlers == null) {
            List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
            this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
        }
    }

    private void initControllerAdviceCache() {
        if (getApplicationContext() == null) {
            return;
        }

        List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());

        List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

        for (ControllerAdviceBean adviceBean : adviceBeans) {
            Class<?> beanType = adviceBean.getBeanType();
            if (beanType == null) {
                throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
            }
            // 缓存所有modelAttribute注解方法
            Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
            if (!attrMethods.isEmpty()) {
                this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
            }
            // 缓存所有initBinder注解方法
            Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
            if (!binderMethods.isEmpty()) {
                this.initBinderAdviceCache.put(adviceBean, binderMethods);
            }
            if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
                requestResponseBodyAdviceBeans.add(adviceBean);
            }
        }

        if (!requestResponseBodyAdviceBeans.isEmpty()) {
            this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
        }
    }

@ExceptionHandler处理

@ExceptionHandler显然是在上述initHandlerExceptionResolvers(context)方法中。同样的，从BeanFactory中获取HandlerExceptionResolver

    /** * Initialize the HandlerExceptionResolver used by this class. * <p>If no bean is defined with the given name in the BeanFactory for this namespace, * we default to no exception resolver. */
    private void initHandlerExceptionResolvers(ApplicationContext context) {
        this.handlerExceptionResolvers = null;

        if (this.detectAllHandlerExceptionResolvers) {
            // Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
            Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
                    .beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
                // We keep HandlerExceptionResolvers in sorted order.
                AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
            }
        }
        else {
            try {
                HandlerExceptionResolver her =
                        context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
                this.handlerExceptionResolvers = Collections.singletonList(her);
            }
            catch (NoSuchBeanDefinitionException ex) {
                // Ignore, no HandlerExceptionResolver is fine too.
            }
        }

        // Ensure we have at least some HandlerExceptionResolvers, by registering
        // default HandlerExceptionResolvers if no other resolvers are found.
        if (this.handlerExceptionResolvers == null) {
            this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
            if (logger.isTraceEnabled()) {
                logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
                        "': using default strategies from DispatcherServlet.properties");
            }
        }
    }

我们很容易找到ExceptionHandlerExceptionResolver

同样的在afterPropertiesSet去处理advice

    @Override
    public void afterPropertiesSet() {
        // Do this first, it may add ResponseBodyAdvice beans
        initExceptionHandlerAdviceCache();

        if (this.argumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
            this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        if (this.returnValueHandlers == null) {
            List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
            this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
        }
    }

    private void initExceptionHandlerAdviceCache() {
        if (getApplicationContext() == null) {
            return;
        }

        List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
        for (ControllerAdviceBean adviceBean : adviceBeans) {
            Class<?> beanType = adviceBean.getBeanType();
            if (beanType == null) {
                throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
            }
            ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
            if (resolver.hasExceptionMappings()) {
                this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
            }
            if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
                this.responseBodyAdvice.add(adviceBean);
            }
        }
    }

示例源码

https://github.com/realpdai/tech-pdai-spring-demos

SpringBoot接口 - 如何统一异常处理

# SpringBoot接口 - 如何统一异常处理

# 为什么要优雅的处理异常

# 实现案例

# @ControllerAdvice异常统一处理

# Controller接口

# 运行测试

# 进一步理解

# @ControllerAdvice还可以怎么用？

# @ControllerAdvice是如何起作用的（原理）？

# 示例源码

SpringBoot接口 - 如何统一异常处理

为什么要优雅的处理异常

实现案例

@ControllerAdvice异常统一处理

Controller接口

运行测试

进一步理解

@ControllerAdvice还可以怎么用？

@ControllerAdvice是如何起作用的（原理）？

示例源码