SpringBoot接口 - 怎么处理Controller异常

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 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@RestControllerAdvicepublic 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 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 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 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 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

@InitBinderpublic 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 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}.    */@Overrideprotected void onRefresh(ApplicationContext context) {    initStrategies(context);}/**    * Initialize the strategy objects that this servlet uses.    * 
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 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

@Overridepublic void afterPropertiesSet() {    // Do this first, it may add ResponseBody advice beans    initControllerAdviceCache();    if (this.argumentResolvers == null) {        List resolvers = getDefaultArgumentResolvers();        this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);    }    if (this.initBinderArgumentResolvers == null) {        List resolvers = getDefaultInitBinderArgumentResolvers();        this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);    }    if (this.returnValueHandlers == null) {        List handlers = getDefaultReturnValueHandlers();        this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);    }}private void initControllerAdviceCache() {    if (getApplicationContext() == null) {        return;    }    List adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());    List